1. Introduction
Diazines and their benzoannulated counterparts represent an important class of chemical compounds applied in numerous areas of chemistry, medicine and technology. Over the last two decades, there has been a remarkable increase in the number of fluorescent diaza-heterocycles [1,2,3,4]. Among them quinoxaline and quinazoline derivatives are considered as pH sensors [5,6,7], luminescent detectors [8,9,10], imaging agents [11], components for organic light-emitting diodes (OLED) materials [12,13], solar cells and organic photovoltaic [14,15], and so on. The fundamental work has been done for the establishment of detailed structure–property relationships (SPRs) providing beneficial information for fine-tuning of the key properties and the rational design and synthesis of fluorophores. For example, the meta-linked D–A architecture in mTPA–phenanthroimidazole was applied for synthesis of near ultraviolet emissive materials [16]. The presence of rotatable groups is known to be favorable for aggregation induced/enhanced emission, and some of substituted benzodiazine derivatives display these properties [17,18]. The introduction of dibenzoannulated azines in the core, as well as attaching of cyano group to the ring, were demonstrated as effective approaches to develop thermally activated delayed fluorescent (TADF) emitters [19,20,21,22].
Quinazolin-4(3H)-one represents diaza-heterocycle with electronic structure similar to quinazoline core and can be used as an effective electron withdrawing fragment to design push-pull structures. Meanwhile, quinazolinone-based molecules of donor-acceptor type have not been properly explored, and the data is limited. However, carbazolyl-substituted quinazolinones A were established to be suitable components for fabrication host materials for green and blue phosphorescent organic light-emitting diodes (Figure 1) [23]. Another scientific group showed the ability of quinazolinone-based dyes B to act as fluorescent probes in human cells [24]. 2-Quinolinylquinazolin-4(3H)-one C demonstrated promising sensory properties towards zinc cations [25]; BF2 complexes of 2-pyridinyl quinazolin-4(3H)-ones D displayed strong luminescence both in solution and solid state, as well as large Stokes shift [26,27]. Moreover, 2-(2-hydroxyphenyl)quinazolines E are well known molecules of excited-state intramolecular proton-transfer (ESIPT) type molecules for imaging and detecting purposes [28].
Our research group is working on different 2,4-disubstituted quinazoline fluorophores and investigating the structure-property relations and possible practical applications. Previously, the π-conjugated chromophores with 4-(morpholin-4-yl)quinazoline electron withdrawing part have been obtained, and the influence of nature and length of π-linker on photophysical properties have been studied [29,30]. We succeeded in deepening of our understanding of the pH- and solvent-dependent behavior of these compounds. Moreover, the controlled protonation for generation of white light emission has been demonstrated [30]. Incorporation of 4-cyanoquinazoline or quinazolin-4(3H)-one cores allows to reinforce the electron-withdrawing properties. We described synthesis and photophysical properties of 4-cyano-2-thienylquinazoline derivatives [31], and we confirmed the strong electron withdrawing nature of 4-cyanoquinazoline core. On the other hand, quinazolin-4(3H)-one bearing 5-(4-diethylaminophenyl)thiophen-2-yl substituent at the position 2 possesses strong photoluminescence in the solution [32].
Herein we expend the series of quinazolin-4(3H)-ones and their 4-cyano counterparts by the synthesis of chromophores with different π-linkers and arrangement of substituents to handle detailed investigation of SPRs and to discover preferable structures for further practical applications. In the frames of this work, we study key photophysical properties in two solvents (toluene and MeCN). Additionally, we analyze emission behavior in solid state and in MeCN/water mixtures and calculate HOMO/LUMO energy levels.
2. Results
2.1. Synthesis
The synthesis of quinazolinones 4–6 is summarized in Scheme 1. Fluorophores 4, 5 and 6 have been obtained by Suzuki-Miyaura cross-coupling of corresponding 2-bromothienylquinazolin-4(3H)-one 1, 4(3)-bromophenylquinazolin-4(3H)-ones 2, 3 with arylboronic acid or arylboronic acid pinacol ester under typical conditions in moderate to good yields (49–84%), Scheme 1. The starting bromine derivatives 1–3 for cross-coupling reactions were obtained and described previously [30,32].
Synthetic approach to 4-cyano-2-thienylquinazolines 7 was developed by our research group earlier [31,32]. It includes nucleophilic substitution of chorine atom at position 4 of quinazoline core by the CN group in DMF under heating and subsequent Suzuki-Miyaura cross-coupling with arylboronic acid. The same route was used for novel π-conjugated chromophores 8 and 9 with 1,4-phenylene or 1,3-phenylene linker (Figure 2) starting from described 2-(4(3)-bromophenyl)-4-chloroquinazolines (yields 13–56%) [30]. Remarkably, cyanation of 4-chloroquinazolines with potassium cyanide results in 4-cyano intermediates in 92% and 94% yield, and the yields are higher compared to 2-thienyl counterpart [32].
Finally, we have synthesized 4-cyano-2-(4-diphenylaminophenyl)quinazoline 11 with shortened π-system compared to derivative 8b (Scheme 2). Quinazolin-4(3H)-one 10 underwent chlorination and subsequent nucleophilic substitution by cyanide residue. We failed to isolate the intermediate 4-chloroquinazoline. Moreover, the yield of target product 11 was 28%. Probably the strong electron-donating effect of the TPA unit causes the chlorination step to be sluggish, leading to the low yield of 11.
The target chromophores 4–6, 8, 9 as well as 11 were characterized by 1H, 13C NMR spectroscopy, mass spectrometry and elemental analysis data. 13C NMR data for sample 6a has not been obtained due to its poor solubility in organic solvents (including DMSO-d6 under heating).
Single crystals of quinazoline 11 were obtained by a slow evaporation technique (n-hexane/chloroform mixture as a solvent) and analyzed by X-ray diffraction analysis (XRD). According to XRD data, the compound is crystallized in the centrosymmetric space group of the triclinic system (Figure 3a).
The mean bond distances and angles of the molecule (Tables S1 and S2, Supplementary Materials) are near to standard values. The molecule is non-planar, and Ph-substituents of the NPh2-groups are turned on the high angle toward the plane of the nitrogen atom (Figure 2b and Figure S17a). The nitrogen of the C6H4-NPh2 group is practically planar. The atom N is deviated from the plane C(13)C(23)C(14) on the 0.054 Å and demonstrates significant conjugation with phenylene moiety (distances N(4)C(14) = 1.402(3), N(4)C(13) = 1.433(3), N(4)C(23) = 1.430(2) Å). Any significantly shortened intermolecular contacts or any special packing in the crystal were not observed.
2.2. UV/Vis and Fluorescence Spectroscopy
UV/Vis and photoluminescence (PL) spectra of compounds 4b,c, 5a,b, 6a,b, 8a,b and 9–11 in toluene (εr = 2.38) [33] and acetonitrile (εr = 36.64) [33] are presented in Figure S16–S28, Supplementary Materials. The main characteristics for described 4a, 7a–c and novel fluorophores are combined in Table 1.
In general, the positions of the longest wavelength absorption bands of quinazolin-4(3H)-ones 4–6, 10 are observed in the UV or purple region (292–410 nm) depending on donor and π-linker nature, arrangement of substituents at phenylene ring as well as solvent polarity. Considering the electron donating influence we note that Et2N- and Ph2N- counterparts in series 4 and 5 display similar position of absorption maxima (λabs = 410 nm for 4a, λabs = 405 nm for 4b, λabs = 370 nm for 5a and λabs = 370 nm for 5b in toluene (Table 1, Figure 4a). Carbazolyl-derivatives 4c and 5c show typical considerable hypochromic shift with maxima at 370 nm (4c) and 342 nm (5c) compared to their diethyl and diphenyl counterparts (Table 1, Figure 4a), that can be explained by shortened D–A conjugation due to rigid structure of carbazolyl unit and twisted configuration of molecule. The results are consistent with our previous research on quinazolines of linear structure [30] and with literature data [34,35]. The change of solvent polarity (from toluene to MeCN) leads to a hypsochromic shift of absorption maximum by 3–10 nm (compounds 4a–c, 5a–c).
The influence of π-linker nature on absorption band is shown on Figure 4b. 2-Thienylquinazolin-4(3H)-one 4b displays strong absorption band around 410 nm in toluene which is bathochromically shifted relative to other diphenylaminoquinazolines 5b, 6b and 10. Compounds 5b and 10 display similar shape and position of absorption band both in toluene and MeCN solution (Figure 4b, Table 1). 2-(Meta-triphenyl)phenylquinazolin-4(3H)-one 6b shows broad absorption band around 328 nm which is hypsochromically shifted by 42 nm in toluene and 32 nm in MeCN compared to para-substituted 2-phenylquinazoline 5b (Table 1). Probably, a meta-linked D–A architecture results in breaking the conjugation between D and A and reflects in blue-shifted absorption. Worse conjugation in bipolar molecules containing meta-phenylene linker and larger dihedral angle, leading to increased steric hindrance, as well as shortened electron delocalization, were reported [36].
Studied quinazolin-4(3H)-ones 4–6, 10 exhibit fluorescence maxima in the range from 430 nm to 490 nm in toluene and from 408 to 560 nm in MeCN. The influence of solvent polarity on emission is considerable, that emphasizes the high polarized excited state of the chromophores. As we expected, 2-thienylquinazolin-4(3H)-one with Et2N group 4a possessed the most longwave emission in toluene. When going to Ph2N and then to carbazolyl counterparts (4b and 4c, respectively) we observed shift to shorter wavelength, and the introduction of the carbazolyl unit has a more significant impact. The same correlation was noted for the second series, 2-(4-aryl)phenylquinazolinones 5a–c (Figure 4a) and, more or less, for 2-(3-aryl)phenylquinazolinjnes 6a–c. The replacement of thienylene linker with phenylene one also leads to a hypochromic shift of emission (for example, chromophores 5b, 6b and 10 in comparison with 4b, Figure 4b).
The quantum yields of chromophores measured by relative method vary over a wide range: for example, QY of thienylene-contained chromophores reaches 82% in toluene (in case of compound 4b). 2-Phenyl-derivatives 5a and 5b demonstrate the increase in QY in both solvents compared to counterparts 4a and 4b with the strongest emission for chromophore 5b (ΦF = 89%). The meta-phenylene quinazolin-4(3H)-ones 6a–c is less emissive with the QY up to 23% (compound 6b in toluene). Notably, the strongest emission is observed for toluene solution of diphenyl-containing quinazolinones 4b, 5b and 6b in each series. When going to MeCN, the QY decreases in the case of Et2N and Ph2N derivatives, probably, due to stabilization of intramolecular change transfer state and enhancement of non-radiative decay. Contrary, carbazolyl-derivatives 4c, 5c and 6c demonstrate opposite result. Such an influence of the carbazolyl-phenyl residue may be due to the destruction of the conjugation resulting from the withdrawal of the phenylene fragment from the quinazoline plane as it was previously noted for 4-(4-(9H-carbazol-9-yl)phenyl)-2-phenyl and 2-quinolyl quinazolines [37,38].
The introduction of the CN group at position 4 of the quinazoline core led to great change in photophysical properties. In absorption spectra of 7a–c and 8a,b, we observed the main longwave band at 365–402 nm and weak band as a shoulder at 415–475 nm in toluene (Figure 5a). Upon excitation the chromophores display emission band with two peaks (Table 1, Figure 5a). The presence of shoulder-type peak in absorption spectra and double peak emission may be raised from the formation of dimers or aggregation between chromophore and solvent molecules. The absorption band of meta-phenylene derivative 9 is hypsochromically shifted in comparison with thienylene counterpart 7b due to less effective conjugation of bi-phenyl moiety and large twisting of the phenylene ring with neighboring units in the π-bridge. The intense peaks of 4-cyanoquinazoline 11 at 367 nm in toluene and 360 nm in MeCN originate from transitions of the main conjugated skeleton, and the weaker peak at 432 and 415 nm is attributed to charge transfer (CT) transitions (Figure 5). The fluorescence quantum yields of CN-derivatives are lower compared to quinazolinone counterparts and do not exceed 23% in toluene. In more polar solvent (MeCN) the values of QY decrease; in the case of compound 11 the quenching of luminescent properties is observed.
In comparison with 4-(morpholin-4-yl)quinazolines [30] quinazolin-4(3H)-one derivatives show bathochromic shift in both absorption and emission maxima that ascribes to better conjugation and stronger electron accepting quinazolinone fragment.
The time-resolved emission data were measured to further characterize the emission bands. The average lifetimes are presented in Table 2 and more detailed measurements are combined in Supplementary Materials, Table S3 and Figures S29–S45. The lifetimes were mono-, bi- or three-component depending on structure and solvent polarity. In toluene, the compounds 4a,b demonstrate the close values of 1.94 ns and 1.90 ns, respectively. The emission lifetime of carbazolyl derivative 4c is lower (0.75 ns). Quinazolines 5a–c with 1,4-phenylene moiety show the similar correlation between electron donating part nature and emission lifetime. In MeCN solution, the lifetime of both series 4 and 5 increases, reaching 2.54–3.66 ns (Table 2). Meta-substituted compounds 6b,c and 2-diphenylaminophenylquinazolin-4(3H)-one counterpart 14 display longer luminescence lifetime in MeCN compared to the toluene solution.
The lifetimes of 4-cyano derivatives are more complicated, probably, due to the formation of dimers, in addition to structural and solvent reasons. The scope of fluorescence lifetime data predicts the existence of several fluorescent species corresponding to locally exited (LE), intramolecular charge transfer (ICT), twisted intramolecular charge transfer (TICT) states [39] for some quinazoline derivatives that requires more carefully experiments in different media, concentrations and so on, and these investigations are in the progress.
2.3. Photoluminescence Data for Compounds 4–7 and 8–11 in Solid State and in MeCN/Water Mixture
Synthesized fluorophores 4–11 exhibit emission in the solid state under UV-irradiation (Figure 6).
Further, the emission spectra of these compounds were recorded, and the data are presented in Table 3 and Figure S46. The quinazolinone derivatives 4a–c, 5a–c, 6a–c and 10 possess dark blue (6c) to yellow (10) emission with maxima from 407 to 537 nm (Figure 7а and Figure S46). The commission international de L’Eclairage (CIE) coordinates from (0.19, 0.13) to (0.14, 0.21) (Figure 7b) were observed for fluorophores 5а-с, 6b,с demonstrating blue emission. In general, when going from solution to solid state, we observed blue shift of emission maximum for derivatives 4a–c, 5a–c, 6a–c to blue region (Table 3).
In terms of the chemical structure, the observed differences in solid-state emission appeared to depend on the electron donating residue and π-linker nature, and substituents arrangement (para or meta). Diphenylamino-derivatives 4b, 5b and 6b demonstrate the strongest emission intensity in their series 4, 5 and 6. Linear non-planar chromophores 5a–c with 1,4-phenylene spacer show the highest quantum yield compared to thienylene and 1,3-phenylene-containing counterparts 4a–c and 6a–c, respectively. The differences can be ascribed to the changing dihedral angle between fragments in the molecule, intermolecular interactions, and intermolecular packing modes caused by the variation in their terminal group and π-linker. Probably, phenylene moiety is turned from the plane of molecule, and the twisted structure prevents close packing that leads to blue shifted emission and intensity enhancement regarding to thienylene counterparts.
The introduction of the CN-group into position 4 of quinazoline core leads to red/orange-colored compounds with poor emission under UV-light (Figure 6). The emission spectra of cyano-derivatives 7a–c [31], 8a,b and 9 display two maxima with low intensity (Table 2). The dual emission can be ascribed to stabilization of two lowest exited states (ICT and TICT) caused by dimer formation through the CN group [32]. The quinazoline chromophore 11 with shortened π-conjugation demonstrates only one emission peak in powder and the highest QY of 3%. According to X-ray analysis, any significantly shortened intermolecular contacts have not been observed and, probably, the molecule forms the only exited state. Notably, the threefold increase in QY value was observed on passing from quinazolinone 10 to its cyano-counterpart 11 (Table 3).
It is well known that molecules displaying aggregation induced emission (AIE) have enormous potential for practical application. Frequently, AIE-active compounds show mechanochromic properties [40]. Generally, AIE phenomena can be caused by restriction of intramolecular motions (RIM) or TICT-state inhibition accompanied by aggregation [41]. By manipulating the aggregation/disaggregation process, various fluorescence turn-on probes based on AIE-active luminophores have been fabricated for the sensitive detection of different analytes.
To study the AIE phenomenon for chromophores, we have analyzed emission behavior of some samples upon addition of water to MeCN solution. For the experiment, we chose Ph2N-containing chromophores 5b and 6b that demonstrated the highest emission in solid state. Quinazoline 11, being not emissive in MeCN and possessing luminescence properties in solid, was analyzed, as well. Compounds 5b and 6b emit in pure MeCN at 535 and 560 nm, respectively. The addition of the first portion of water (up to 60%) to solution of 5b leads to a gradual decrease in intensity and red shift of maximum caused by the increase in solvent polarity, and probably to stabilization of non-radiative TICT state (Figure S47). At 65% water content, the blue shifted maximum appears at 470 nm and the intensity increase with further addition of water. More intensive emission was observed at 80% water fraction compared to pure MeCN, and further slight decrease up to initial intensity was noticed. The compound 6b possesses poor emission in pure MeCN. The luminescence is fully quenched after the addition of 10% of water and appears at 70% with blue-shifted maximum (Figure S48). At high water content, the plot of I/I0 versus water fraction has a similar profile to that of quinazoline 5b. Compound 11, which is non-emissive in pure MeCN, demonstrates gradual emission enhancement after the addition of 75% of water (Figure S49). The appearance of a blue-shifted emission band at a large amount of water in the case of derivatives 5b and 6b is probably caused by nanoaggregates formation. Moreover, the emission was even stronger relative to the original MeCN solution when the water content is larger than 90%. To clarify the difference in behavior of triphenylamino quinazoline derivatives 5b, 6b, 11 in MeCN/water mixtures, a more detailed study of aggregation processes is required, which is beyond the scope of this research.
2.4. Quantum-Chemical Calculations
Further, we performed the DFT calculations of quinazolin-4(3H)-ones 4a–c, 5a–c, 6a–c, 10 and 4-cyanoquinazolines 8a,b, 9, 11 in gas phase at the B3LYP/6–311 G* level using the Orca 4.0.1 software package [42,43,44,45,46] and conducted the chemical optimization on their energy levels based on DFT/B3LYP/6-31G (d,p) using Gaussian 09. The HOMO and LUMO energy levels of compounds 4–6, 10 are in the range of −5.20 to −5.80 eV and −1.65 to −2.25 eV, respectively, with an energy band gap (ΔE) ranging from 3.20 to 4.05 eV (Figure 8). The smallest band gap is observed for dye 4b bearing 5-(4-diphenylaminophenyl)thiophenylene substituent. Introduction of the CN group in the position 4 of quinazoline core leads to a significant decrease in the band gap (2.33–2.61 eV), mainly due to lowering of LUMO energy (Figure 8). The energy levels of quinazolinone derivatives 4–6, 10 have changed slightly regarding to 4-morpholinyl counterparts [30].
The spatial distributions of the calculated HOMO and LUMO energy levels of fluorophores are shown in Table S3. The HOMO of 2-aryl/thienylquinazolin-4(3H)-ones 4a–c, 5a–c, 6a–c, 10 is basically distributed over the electron donating diethylaminophenyl, diphenylaminophenyl or (carbazol-9-yl)phenyl unit, and the LUMO of 2-aryl/thienyl quinazolin-4(3H)-ones is mainly localized at quinazolin-4(3H)-one unit and its neighboring 2-phenyl or 2-thienyl substituent. In the case of 4-cyano derivatives, the localization of HOMO level is similar to 4-oxo counterparts, whereas LUMO is distributed on 4-cyanoquinazoline fragment (Table S4), probably the strong electron deficient cyano substituent stabilizes the excited state. When compared to the quinazolinones derivatives, the HOMO and LUMO distributions of 4-cyanoquinazolins are barely overlapped.
3. Experimental Methods
3.1. General Information
Unless otherwise indicated, all common reagents and solvents were used by commercial suppliers without further purification. Melting points were determined on Boetius combined heating stages. 1H NMR and 13C NMR spectra were recorded at room temperature at 400 and 100 MHz respectively, on a Bruker DRX-400 spectrometer; or at 151 MHz on a Bruker DRX-600 spectrometer (13С NMR spectra for compounds 4b,c). Hydrogen chemical shifts were referenced to the hydrogen resonance of the corresponding solvent (DMSO-d6, δ = 2.50 ppm or CDCl3, δ = 7.26 ppm). Carbon chemical shifts were referenced to the carbon resonances of the solvent (DMSO-d6, δ = 39.5 ppm CDCl3, δ = 77.2 ppm). Peaks are labeled as singlet (s), doublet (d), triplet (t), quartet (q) and multiplet (m). Mass spectra were recorded on the SHIMADZU GCMS-QP2010 Ultra instrument with electron ionization (EI) of the sample. Microanalyses (C, H, N) were performed using the Perkin–Elmer 2400 elemental analyzer.
3.2. Photophysical Characterization
UV/Vis spectra were recorded with Shimadzu UV-2600 spectrophotometer. Photoluminescent spectra were recorded on a Varian Cary Eclipse spectrofluorometer. UV/Vis and fluorescence spectra of solutions were recorded using standard 1 cm quartz cells at room temperature. The ФF values were calculated using the established procedure with 3-aminophalimide in ethanol (ФF = 0.60) and in quinine sulfate 0.1N H2SO4 (ФF = 0.55) [47]. Fluorescence spectra in a solid state were measured by the integrating sphere Quanta-φ F-3029 at Horiba FluoroMax-4.
The emission lifetimes have been measured using the TCSPC option of FS5 Edinburgh Instruments spectrofluorometer. The sample has been excited by EPLED-300 picosecond pulsed light emitted diode centered at 300 nm and EPL-375 picosecond pulsed diode laser centered at 375 nm. The instrument response function (IRF) has been recorded under described conditions by replacing the sample with a silica diffuser. The time decay data have been analyzed by nonlinear least-squares fitting with the deconvolution of the IRF using the Fluoracle software package.
Analytical experiments were carried out by using equipment from the Center for Joint Use «Spectroscopy and Analysis of Organic Compounds» at the Postovsky Institute of Organic Synthesis of the Ural Branch of the Russian Academy of Sciences.
3.3. Crystallography
The single crystal (red block of 0.45 × 0.35 × 0.25) of compound 11 was used for X-ray analysis. The single crystals XRD experiment was performed for compound 11 on an automated diffractometer “Xcalibur 3” with a standard procedure (graphite-monochromated Mo Kα-irradiation, T = 295(2) K, ω-scanning with step 1°). An empirical absorption correction was applied. Using Olex2 [48], the structure was solved with the ShelXT structure solution program using Intrinsic Phasing and refined with the ShelXL [49] refinement package using full-matrix Least Squares minimization. All non-hydrogen atoms were refined in an anisotropic approximation; the H-atoms at the C(5)–C(8) carbons were solved by direct method and were refined independently in the isotropic approximation, all other H-atoms were placed in the calculated positions and refined isotropically in the “rider” model.
Crystal data for 11 C27H18N4, M = 398.45, triclinic, a = 9.1982(9) Å, b = 9.8103(10) Å, c = 12.9224(11) Å, α = 96.908(8)°, β = 107.028(8)°, γ = 105.834(9)°, V = 1046.95(18) Å3, space group P–1, Z = 2, μ(Mo Kα) = 0.076 mm−1. On the angles 3.61 < 2Θ < 30.98°, 8589 reflections measured, 5685 unique (Rint = 0.0528) which were used in all calculations. Goodness to fit at F2 0.991; The final R1 = 0.1425, wR2 = 0.2096 (all data) and R1 = 0.0668, wR2 = 0.1481 (I > 2s(I)). Largest diff. peak and hole 0.263 and −0.203 ēÅ−3.
The result of X-ray diffraction analysis for compound 11 was deposited in the Cambridge Crystallographic Data Centre (CCDC 2141460). The data is free and can be available at
3.4. Preparation of Intermediates
Starting quinazolinones 1, 2, 3 and 10, as well as the corresponding 4-chloro derivatives, were synthesized as described in our previous works [30,32].
2-(4-Bromophenyl)- and 2-(3-bromophenyl)-4-cyanoquinazolines (bromo derivatives I and II) were obtained similar to described procedure [32]. Freshly prepared potassium cyanide (0.25 g, 3.8 mmol) and sodium p-toluenesulfonate (0.20 g, 1.0 mmol) were added to a solution of 4-chloro derivative (3 mmol) in dry DMF (12 mL). The mixture was heated at 95 °С for 3 h. After cooling the precipitate was filtered off and washed with water (30 mL) and EtOH (5 mL).
2-(4-Bromophenyl)-4-cyanoquinazoline (I): pale brown solid, yield 92%; mp > 300 °C; 1H NMR (DMSO-d6, 400 MHz) δ 7.74 (2H, d, 3J = 8.3 Hz, H-3′, H-5′), 7.95 (1H, m), 8.20 (2H, m), 8.26 (1H, d, 3J = 8.3 Hz), 8.48 (2H, d, H-2′, H-6′, 3J = 8.3 Hz); EIMS m/z 312 [M + 3]+ (17), 311 [M + 2]+ (92), 310 [M + 1]+ (18), 309 [M]+ (100), 285 (10), 259 (13), 257 (14), 178 (20), 151 (15), 115 (27), 102 (45), 101 (13), 76 (43), 75 (32), 51 (14), 50 (30); anal. C 58.12, H 2.58, N 13.57%, calcd for C15H8BrN3 (310.15), C 58.09, H 2.60, N 13.55%.
2-(3-Bromophenyl)-4-cyanoquinazoline (II). Pale brown solid, yield 94%; mp > 300 °C; 1H NMR (DMSO-d6, 400 MHz) δ 7.55 (1H, m, H-5′), 7.77 (1H, m, H-4′), 7.97 (1H, m), 8.22–8.28 (3H, m), 8.53 (1H, d, 3J = 7.8 Hz, H-6′), 8.65 (1H, s, H-2′); EIMS m/z 312 [M+3]+ (18), 311 [M + 2]+ (94), 310 [M + 1]+ (19), 309 [M]+ (100), 230 (40), 178 (27), 177 (11), 151 (19), 115 (31), 102 (50), 101 (14), 76 (52), 75 (38), 74 (11), 51 (19), 50 (40); anal. C, 58.13; H, 2.63; N, 13.59%, calcd for C15H8BrN3 (310.15), C 58.09, H 2.60, N 13.55%.
3.5. General Procedures of Suzuki Cross-Coupling
To mixture of bromo derivative 1, 2, 3, I or II (0.65 mmol) in toluene (10 mL) the corresponding boronic acid or boronic acid pinacol ester (0.70 mmol), PdCl2(PPh3)2 (46 mg, 65 μmol), PPh3 (34 mg, 130 μmol), saturated solution of K2CO3 (3.7 mL) and EtOH (3.7 mL) were added. The mixture was stirred at 85 °C for 7–20 h in argon atmosphere in round-bottom pressure flask. The reaction mixture was cooled. After cooling, the target product was filtered off and washed with water and hexane [29,30,31].
3.6. Derivatives of 2-Arylthienylquinazolin-4(3H)-ones 4
2-(5-(4-N,N-Diphenylaminophenyl)thiophen-2-yl)quinazolin-4(3H)-one (4b). The reaction mixture was heated for 9 h. Green yellow solid, yield 81%; mp > 300 °C; 1H NMR (DMSO-d6, 400 MHz) δ 7.02–7.10 (8H, m), 7.29 (4H, m), 7.37 (1H, d, 3J = 3.2 Hz), 7.42 (1H, m), 7.59 (3H, m), 7.73 (1H, m, CH quinaz.), 8.10 (1H, d, 3J = 7.7 Hz), 8.17 (1H, m), 12.51 (1H, s, NH); 13С NMR (DMSO-d6, 151 MHz), δ 120.7, 122.2, 123.6, 123.7, 124.6, 125.9, 126.1, 126.4, 126.7, 126.8, 129.6, 130.5, 134.5, 135.0, 146.6, 147.7, 148.6, 161.7. EIMS m/z 473 [M + 2]+ (11), 472 [M + 1]+ (36), 471 [M]+ (100), 235 (13); anal. C 76.45, H 4.47, N 8.94%, calcd for C30H21N3S (471.57) C 76.41, H 4.49, N 8.91%.
2-(5-(4-(9H-Carbazol-9-yl)phenyl)thiophen-2-yl)quinazolin-4(3H)-one (4c). The reaction mixture was heated for 10 h. Dark yellow solid, yield 74%; mp > 290 °C; 1H NMR (DMSO-d6, 400 MHz) δ 7.28 (2H, m, 2 CH carbaz.), 7.40–7.48 (5H, m), 7.64–7.77 (4H, m), 7.76 (1H, m, CH quinaz.), 8.02 (2H, d, 3J = 8.0 Hz), 8.13–8.19 (3H, m), 8.27 (1H, m), 12.63 (1H, s, NH); 13С NMR (DMSO-d6, 151 MHz) δ 109.7, 120.2, 120.5, 120.8, 122.8, 125.4, 125.9, 126.2, 126.8, 127.2, 127.4, 128.1, 128.8, 130.6, 131.9, 13.6, 136.6, 137.0, 139.9, 147.4, 148.5, 161.7; EIMS m/z 471 [M + 2]+ (11), 470 [M + 1]+ (36), 469 [M]+ (100), 350 (13), 235 (17), 92 (16), 91 (18); anal. C 76.76, H 4.11, N 8.93%, calcd for C30H21N3OS (469.56), C 76.74, H 4.08, N 8.95%.
3.7. Biphenylene-Containing Quinazolin-4(3H)-ones 5, 6
2-(4’-N,N-Diethylamino[1,1’-biphenyl]-4-yl)quinazolin-4(3H)-one (5a). The reaction mixture was heated for 20 h. Grey solid, yield 69%; mp 265–267 °C; 1H NMR (CDCl3, 400 MHz) δ 1.22 (6H, t, 3J = 7.0 Hz, 2 CH3), 3.43 (4H, q, 3J = 7.0 Hz, 2 CH2), 6.78 (2H, d, 3J = 8.7 Hz, H-3″, H-5″), 7.49 (1H, m, CH quinaz.), 7.58 (2H, d, 3J = 8.7 Hz, H-2″, H-6″), 7.74–7.84 (4H, m, H-3′, H-5′, 2 CH quinaz.), 8.14 (2H, d, 3J = 8.2 Hz, H-2′, H-6′), 8.33 (1H, d, 3J = 8.0 Hz, CH quinaz.), 10.26 (1H, s, NH); 13C NMR (DMSO-d6, 100 MHz) δ 12.5 (2CH3), 43.7 (CH2), 111.8, 121.3, 124.7, 125.4, 125.8, 126.8, 127.5, 128.3, 132.9, 138.2, 142.0, 147.2, 150.1. EIMS m/z 370 [M + 1]+ (17), 369 [M]+ (59), 355 (28), 354 [M-СН3]+ (100), 326 [M-HNCO]+ (13), 177 (12), 119 (29); anal. C 78.04, H 6.28, N 11.36%, calcd for C24H23N3O (369.47), C 78.02, H 6.27, N 11.37%.
2-(4’-N,N-Diphenylamino[1,1’-biphenyl]-4-yl)-quinazolin-4(3H)-one (5b). The reaction mixture was heated for 10 h. Pale yellow solid, yield 84%; mp 265–267 °C; 1H NMR (CDCl3, 400 MHz) δ 7.09 (2H, m), 7.18 (6H, m), 7.28–7.34 (4H, m), 7.52 (1H, m, CH quinaz.), 7.58 (2H, d, 3J = 8.6 Hz, H-2″, H-6″), 7.79–7.87 (4H, m, 2 CH quinaz., H-3′, H-5′), 8.23 (2H, d, 3J = 8.6 Hz, H-2′, H-6′), 8.36 (1H, d, 3J = 8.0 Hz, CH quinaz.), 10.59 (1H, s, NH); 13C NMR (DMSO-d6, 100 MHz) δ 121.2, 122.9, 123.2, 124.1, 124.8, 125.5, 125.6, 126.7, 127.5, 128.2, 129.4, 132.9, 132.9, 133.6, 141.3, 146.8, 147.1, 149.6, 154.8, 164.9. EIMS m/z 466 [M + 1]+ (36), 465 [M]+ (100); anal. C 82.57, H 4.99, N 9.01%, calcd for C32H23N3O (465.56), C 82.56, H 4.98, N 9.03%.
2-(4’-9H-Carbazol-9-yl[1,1’-biphenyl]-4-yl)-quinazolin-4(3H)-one (5c). The reaction mixture was heated for 20 h. Grey solid, yield 75%; mp 287–289 °C; 1H NMR (DMSO-d6, 400 MHz) δ 7.27 (2H, m, 2 CH carbaz.), 7.42 (5H, m), 7.67–7.74 (4H, m), 7.89 (2H, d, 3J = 8.6 Hz), 8.03 (2H, d, 3J = 8.6 Hz), 8.13–8.19 (3H, m, 2 CH phenylene, CH quinaz.), 8.45 (2H, d, 3J = 8.6 Hz), 10.59 (1H, s, NH); 13C NMR (DMSO-d6, 100 MHz) δ 109.73, 120.1, 120.5, 122.8, 126.1, 126.3, 127.1, 128.3, 128.5, 131.1, 136.2, 139.0, 139.6, 140.1, 151.6. MS m/z 464 [M + 1]+ (38), 463 [M]+ (100), 344 (21), 119 (17); anal. C 82.90, H 4.59, N 9.06%, calcd for C32H21N3O (463.54), C 82.92, H 4.57, N 9.07%.
2-(4’-(Diethylamino)-[1,1’-biphenyl]-3-yl)quinazolin-4(3H)-one (6a). The reaction mixture was heated for 10 h. Additionally, the solid was washed with CH2Cl2. Dark grey solid, yield 49%; mp 245–247 °C; 1H NMR (DMSO-d6, 400 MHz) δ 1.19 (6H, t, 3J = 6.9 Hz, 2 CH3), 3.42 (4H, d, 3J = 6.9 Hz, 2 CH2), 6.73 (2H, d, 3J = 7.6 Hz, H-3″, H-5″), 7.45–7.53 (2H, m), 7.61 (2H, d, 3J = 7.6 Hz, H-2″, H-6″), 7.71–7.80 (3H, m), 8.08 (1H, d, 3J = 7.9 Hz), 8.16 (1H, d, 3J = 8.3 Hz), 8.39 (1H, s, H-2′), 12.53 (1H, s, NH); EIMS m/z 370 [M + 1]+ (15), 369 [M]+ (51), 344 (21), 355 (28), 354 (100), 326 (11), 177 (15), 119 (27); anal. C 78.00, H 6.25, N 11.36%, calcd for C24H23N3O (369.47), C 78.02, H 6.27, N 11.37%.
2-(4’-(Diphenylamino)-[1,1’-biphenyl]-3-yl)quinazolin-4(3H)-one (6b). The reaction mixture was heated for 10 h. Grey solid, yield 55%; mp 260–262 °C; 1H NMR (CDCl3, 400 MHz) δ 7.03 (2H, m), 7.14 (6H, m), 7.23–7.32 (5H, m), 7.60 (1H, m), 7.66 (2H, d, 3J = 7.6 Hz, H-2″, H-6″), 7.71–7.79 (2H, m), 7.83 (1H, d, 3J = 8.3 Hz), 8.18 (1H, d, 3J = 7.6 Hz), 8.24 (1H, d, 3J = 7.6 Hz), 8.46 (1H, s, H-2′), 11.81 (1H, s, NH); 13C NMR (DMSO-d6, 100 MHz) δ 121.1, 123.3, 124.5. 125.4, 125.8, 126.4, 126.5, 127.4, 128.0, 128.9, 129.2. 129.6, 133.4, 133.5, 134.5, 139.9, 147.0, 147.1, 148.8, 152.5, 162.5; EIMS m/z 466 [M + 1]+ (35), 465 [M]+ (100), 464 (12), 233 (12); anal. C 82.55, H 4.96, N 9.01%, calcd for C32H23N3O (465.56), C 82.56, H 4.98, N 9.03%.
2-(4’-(9H-Carbazol-9-yl)-[1,1’-biphenyl]-3-yl)quinazolin-4(3H)-one (6c). The reaction mixture was heated for 12 h. Grey solid, yield 81%; mp > 290 °C; 1H NMR (DMSO-d6, 400 MHz) δ 7.32 (2H, m, 3J = 6.8 Hz, 2CH carbaz.), 7.45–7.50 (4H, m), 7.55 (1H, m), 7.72 (1H, m), 7.78 (3H, m), 7.87 (1H, m), 8.03 (1H, d, 3J = 7.6 Hz), 8.15–8.20 (3H, m), 8.27 (3H, m), 8.61 (1H, s, H-2′), 12.75 (1H, s, NH); 13C NMR (DMSO-d6, 100 MHz) δ 109.5, 119.9, 120.3, 121.0, 122.7, 125.7, 125.8, 126.1, 126.4, 126.9. 127.0, 128.5, 129.2, 129.4, 133.3, 134.3, 136.5, 138.4, 139.5, 140.0, 148.6, 152.0, 162.0; EIMS m/z 464 [M + 1]+ (37), 463 [M]+ (100), 344 (19), 232 (12), 119 (28), 92 (12); anal. C 82.90, H 4.55, N 9.05%, calcd for C32H21N3O (463.54), C 82.92, H 4.57, N 9.07, O 3.45%.
3.8. Biphenylene-Containing 4-Cyanoquinazolines 8, 9
2-(4’-(Diethylamino)-[1,1’-biphenyl]-4-yl)quinazoline-4-carbonitrile (8a). The reaction mixture was heated for 7 h. After cooling the EtOAc/water mixture (1:1, 10 mL) was added. The organic layer was separated, and the aqueous layer was extracted with additional EtOAc (2 × 10 mL). The organic extracts were combined, and the solvent was evaporated under reduced pressure. The product was purified by column chromatography (SiO2, hexane/EtOAc, 3/1). Red solid, yield 13%; mp 145–147 °C; 1H NMR (DCCl3, 400 MHz) δ 1.22 (6H, t, 3J = 6.9 Hz, 2 CH3), 3.43 (4H, q, 3J = 6.9 Hz, 2 CH2), 6.78 (2H, d, 3J = 8.4 Hz, H-3″, H-5″), 7.61 (2H, d, 3J = 8.4 Hz, H-2″, H-6″), 7.75 (3H, m, H-3′, H-5′, CH quinaz.), 8.02 (1H, m, CH quinaz.), 8.17 (1H, d, 3J = 8.6 Hz, CH quinaz.), 8.24 (1H, d, 3J = 7.8 Hz, CH quinaz.), 8.63 (2H, d, 3J = 8.3 Hz, H-2′, H-6′); 13C NMR (CDCl3, 100 MHz) δ 12.8, 44.6, 112.0, 114.7, 123.0, 125.1, 126.3, 126.8, 128.2, 129.2, 129.3, 129.6, 133.8, 135.8, 143.6, 144.5, 147.9, 152.0, 161.3; EIMS m/z 379 [M + 1]+ (16), 378 [M]+ (56), 364 (29), 363 (100) [M-СН3]+, 335 (15), 334 (14), 306 (10), 181 (11); anal. C 79.29, H 5.38, N 14.77%, calcd for C25H22N4 (378.48), C 79.34, H 5.36, N 14.80%.
2-(4’-(Diphenylamino)-[1,1’-biphenyl]-4-yl)quinazoline-4-carbonitrile (8b). The reaction mixture was heated for 7 h. The crude product was isolated from toluene solution similar to 8a. The product was purified by column chromatography (gradually from hexane to hexane/EtOAc (1:19)) and recrystallization from CH2Cl2/hexane mixture. Red-orange solid, yield 56%; mp 105–107 °C; 1H NMR (DCCl3, 400 MHz) δ 7.06 (2H, m), 7.15–7.18 (6H, m), 7.29 (4H, m), 7.59 (2H, d, 3J = 8.7 Hz, H-2″, H-6″), 7.77 (3H, m, H-3′, H-5′, CH quinaz.), 8.04 (1H, m, CH quinaz.), 8.19 (1H, d, 3J = 8.7 Hz, CH quinaz.), 8.26 (1H, d, 3J = 8.2 Hz, CH quinaz), 8.67 (2H, d, 3J = 8.7 Hz, H-2′, H-6′,); 13C NMR (CDCl3, 100 MHz) δ 114.6, 123.1, 123.4, 123.7, 124.8, 125.1, 127.0, 128.0, 129.4, 129.5, 129.6, 133.9, 134.9, 135.9, 143.6, 143.8, 147.7, 148.0, 152.0, 161.0. EIMS m/z 475 [M + 1]+ (39), 474 [M]+ (100), 473 (10), 237 (13); anal. C 83.48, H 4.70, N 11.76%, calcd for C33H22N4 (474.18), C 83.52, H 4.67, N 11.81%.
2-(4’-(Diphenylamino)-[1,1’-biphenyl]-3-yl)quinazoline-4-carbonitrile (9). The reaction mixture was heated for 7 h. The crude product was isolated from toluene solution similar to 8a. The product was purified by column chromatography (SiO2, gradually from hexane to hexane/EtOAc (1:19)) and recrystallization from CH2Cl2/hexane mixture. Red solid, yield 21%; mp 210–212 °C. 1H NMR (CDCl3, 400 MHz) δ 7.05 (2H, m), 7.16–7.21 (6H, m), 7.26-7.31 (4H, m), 7.61 (3H, m, H-2″, H-6″), 7.75–7.81 (2H, m), 8.05 (1H, m), 8.21 (1H, d, 3J = 8.6 Hz), 8.27 (1H, d, 3J = 8.3 Hz), 8.57 (1H, d, 3J = 7.7 Hz), 8.85 (1H, s, H-2′). 13C NMR (CDCl3, 100 MHz) δ 114.6, 123.2, 123.3, 124.1, 124.6, 125.1, 127.2, 127.3, 128.1, 129.5, 129.6, 127.7, 129.9, 134.7, 135.9, 137.0, 141.5, 143.6, 147.7, 147.8, 151.9, 161.1; EIMS m/z 475 [M + 1]+ (38), 474 [M]+ (100); anal. C 83.49, H 4.72, N 11.78%, calcd for C33H22N4 (474.18), C 83.52, H 4.67, N 11.81%.
3.9. 2-(4-(Diphenylamino)phenyl)quinazoline-4-carbonitrile (11)
To quinazolinone 10 (0.30 g, 0.77 mmol) POCl3 (1.0 mL, 10.72 mmol) was added. The mixture was refluxed for 2 h using drying tube containing anhydrous calcium chloride. After cooling, the mixture was poured into ice and formed precipitate was filtered off and washed with saturated NaHCO3 solution. To the crude 4-chloroquinazoline red solid in dried DMF (4.4 mL), KCN (0.1 g, 1.54 mmol) and sodium p-toluenesulfonate (0.10 g, 0.52 mmol) was added, the reaction mixture was refluxed at 95 °C for 3 h. After cooling the water (10 mL) was added and the precipitate was filtered off. The product was purified by column chromatography (SiO2, gradually from hexane/EtOAc (19:1) to EtOAc). Orange solid, yield 28%; mp 150–152 °C; 1H NMR (CDCl3, 400 MHz) δ 7.16–7.26 (8H, m), 7.38 (4H, m), 7.77 (1H, m, CH quinaz.), 8.04 (1H, m, CH quinaz.), 8.16 (1H, d, 3J = 8.9 Hz, CH quinaz.), 8.26 (1H, d, 3J = 8.9 Hz, CH quinaz.), 8.50 (2H, d, 3J = 8.9 Hz, H-2′, H-6′); 13C NMR (CDCl3, 100 MHz) δ 114.7, 121.7, 122.8, 124.2, 125.1, 125.7, 128.9, 129.4, 129.6, 130.0, 135.7, 143.5, 147.1, 151.1, 152.0, 161.0; EIMS m/z 399 [M + 1]+ (31), 398 [M]+ (100), 397 (18); anal. C 81.35, H 4.58, N 14.01%, calcd for C27H18N4 (398.47), C 81.39, H 4.55, N 14.06%.
4. Conclusions
In summary, we have designed a series of push–pull chromophores bearing 2-(aryl/thiophen-2-yl)quinazolin-4(3H)-one and 4-cyano-2-arylquinazoline electron acceptor and Et2N-, Ph2N- or carbazol-9-yl- electron donor fragments. 2-(Aryl/thiophen-2-yl)quinazolin-4(3H)-ones showed fluorescence in blue-green region in solutions, triphenylamino derivative with para-phenylene linker displayed the highest quantum yield of 89% in toluene solution and 39.7% in powder. Strong influence of donor fragment nature on photophysical properties was observed, the fluorescence intensity of Et2N and Ph2N derivatives decreased when going from toluene to MeCN solution, whereas carbazol-9-yl counterparts demonstrated growing of QY. 4-Cyanoquinazolines are less emissive both in solutions and solid state than their quinazolin-4-one counterparts. The introduction of cyano group led to orange/red colored powder and dual emission bands. Emission intensity of some molecules was enhanced upon the addition of water to MeCN solution. 4-Cyanoquinazolines exhibited enhanced intramolecular charge transfer regarding their quinazolin-4-one analogues as was shown by their red-shifted absorption and emission spectra as well as their decreased electrochemical gap by more than 1 eV.
Conceptualization, V.N.C.; methodology, T.N.M. and J.V.P.; investigation, E.F.Z., P.A.S. and G.A.K.; writing—original draft preparation, T.N.M. and E.V.N.; writing—review and editing, G.N.L.; supervision, G.N.L. and E.V.N.; project administration, E.V.N. All authors have read and agreed to the published version of the manuscript.
Not applicable.
Not applicable.
The data are available on request from the corresponding authors.
The authors declare no conflict of interest.
Samples of the compounds 4, 5, 6, 10 are available from the authors.
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Enlarge this image.Figure 3. (a) Molecular structure of 11 in the thermal ellipsoids of 50% probability; (b) Selected torsion angles of compound 11.
Enlarge this image.Figure 4. (a) UV/Vis (dashed line) and photoluminescence (solid line) spectra of compounds 5a–c in toluene; (b) UV/Vis (dashed line) and photoluminescence (solid line) spectra of Ph2N derivatives 4b, 5b, 6b and 10 in toluene.
Enlarge this image.Figure 5. UV/Vis (dashed line) and photoluminescence (solid line) spectra of 4-cyano-derivatives 8a,b, 9 and 11 in toluene (a) and MeCN (b).
Enlarge this image.Figure 6. Emission of compounds 4–11 in solid state (powder). Photographs were taken in the dark upon irradiation with a hand-held UV lamp (λem = 366 nm).
Enlarge this image.Figure 7. (a) Normalized emission spectra of quinazolinones 4–6, 10 in solid state; (b) The CIE chromaticity diagram of blue chromophores 5a–c, 6b,c in solid state.
Enlarge this image.Figure 8. Diagram on HOMO and LUMO energy levels of quinazolin-4(3H)-ones 4a–c, 5a–c, 6a–c, 10 and 4-cyanoquinazolines 8a,b, 9, 11 in gas phase.
Photophysical properties of quinazolin-4(3H)-ones 4–6, 10 and 4-cyanoquinazolines 7–9, 11 in toluene and MeCN solutions.
| Compound | Solvent | λabs, nm |
λex, nm | λem, nm | ΔνSt d, cm−1 | ΦF f, % |
|---|---|---|---|---|---|---|
| 4a [ |
Toluene | 410 (-) a | - c | 490 | 3982 | 71 |
| MeCN | 404 (-) a | - c | 541 | 6368 | 28 | |
| 4b | Toluene | 405 (35.8), 304 (21.8) | 404, 309 | 470 | 3415 | 82 g (380) |
| MeCN | 398, 297, 282 (-) b | 399, 296 | 545 | 6777 | 50 g (380) | |
| 4c | Toluene | 370 (-) b, 290 (-) b | 370 | 430, 456 | 5097 e | 26 (350) |
| MeCN | 363 (-) b | 359 | 490 | 7140 | 43 (360) | |
| 5a | Toluene | 370 (37.1) | 360, 370 | 450 | 4805 | 84 (350) |
| MeCN | 367 (-) b | 367 | 535 | 8556 | 49 (360) | |
| 5b | Toluene | 370 (30.1), 302 (22.5) | 371, 360, 309 | 445 | 4555 | 89 g (380) |
| MeCN | 360, 298 (-) b | 355, 297 | 535 | 9086 | 43 g (380) | |
| 5c | Toluene | 342 (36.5) b | 342 | 415 | 5143 | 3 (350) |
| MeCN | 330 (-) b | 340 | 490 | 9895 | 38 (320) | |
| 6a | Toluene | 310 (33.6) | 325 | 460 | 10,519 | 14 (315) |
| MeCN | 310 (34.2) | 354 | 560 | 14,401 | <1(360) | |
| 6b | Toluene | 328 (39.3), 308 (36.5) | 340 | 430 | 7232 | 23 (328) |
| MeCN | 328 (30.9), 305 (32.1) | 330 | 420, 560 | 12,631 e | 2 (328) | |
| 6c | Toluene | 340sh, 310 (-) b | 352 | broad band |
9002 e | <1 (315) |
| MeCN | 340sh, 302sh, 292 (-)b | 340 | 408 | 9737 | 5 (320) | |
| 10 | Toluene | 367 (33.9), 295 (18.4) | 370, 360, 305 | 430 | 3992 | 71 g (380) |
| MeCN | 359, 292 (-) b | 356, 292 | 500 | 7855 | 46 g (380) | |
| 7a [ |
Toluene | 475 sh, 402 (-) a | - c | 485, 670 | 9950 e | <1 |
| MeCN | 397 (-) a | - c | 564 | 7458 | <1 | |
| 7b [ |
Toluene | 440 sh (18.3), |
450, 400, 302 | 485, 623 | 6171 e | 5 |
| MeCN | 450 sh (16.7), 391 (29.8), |
450, 390, 298 | 525 | 3425 | <1 | |
| 7c [ |
Toluene | 365 (-) a | - c | 452, 538 | 8810 e | 22 |
| MeCN | 356 (-) a | - c | 494 | 7847 | 8 | |
| 8а | Toluene | 425 sh (9.3), 370 (21.3) | 425, 360 | 460, 600 | 6863 e | 7 |
| MeCN | 365 (21.2), 268 (21.5) | 360 | 530 | 8529 | <1 | |
| 8b | Toluene | 415 sh (25.8), 365 (46.6), 347 (46.8) | 415, 340, 310 | 465, 555 | 6078 e | 23 |
| MeCN | 360 (31.1) | 360 | 400, 540 | 2777 e | <1 | |
| 9 | Toluene | 337 sh (31.1), 309 (37.0) | 386, 308 | 468 | 8306 | 15 |
| MeCN | 320 sh (30.0), 306 (33.1) | 380, 295 | 560 | 14,822 | 3 | |
| 11 | Toluene | 432 (11.2), 367 (35.7), |
440, 360, 308 | 570 | 5604 | 15 |
| MeCN | 415 sh (10.7), 360 (36.6), 299 (20.6) | - | - | - | - |
a Not calculated. b Poor solubility. c Not measured. d Stokes shifts were calculated considering the lowest energetic absorption band (in bold). e Relative to major emission maximum (in bold). f Fluorescence quantum yield was determined relative to quinine sulfate in 0.1 N H2SO4 as standard (ΦF = 0.55). g Fluorescence quantum yield was determined relative to 3-aminophthalimide in ethanol as standard (ΦF = 0.60).
Data of the fluorescence lifetime measurements of 4a–c, 5a–c, 6a–c, 10, 7a–c, 8a,b, 9b, 11: τ avg—average lifetime, χ2—chisquared distribution.
| Comp. | Solvent | λem, [nm] | τ avg, [ns] | χ2 | λex, [nm] |
|---|---|---|---|---|---|
| 4a | Toluene | 490 | 1.94 | 1.067 | 375 |
| MeCN | 541 | 2.71 | 1.170 | 375 | |
| 4b | Toluene | 470 | 1.90 | 1.131 | 375 |
| MeCN | 545 | 3.25 | 1.091 | 292 | |
| 4c | Toluene | 430, 456 | 0.75, 0.75 | 1.029, 1.339 | 375 |
| MeCN | 490 | 2.54 | 1.094 | 375 | |
| 5a | Toluene | 450 | 1.38 | 1.126 | 375 |
| MeCN | 535 | 2.64 | 1.164 | 375 | |
| 5b | Toluene | 445 | 1.61 | 1.180 | 375 |
| MeCN | 535 | 3.22 | 1.095 | 375 | |
| 5c | Toluene | 415 | 0.62 | 1.254 | 300 |
| MeCN | 490 | 3.66 | 1.186 | 300 | |
| 6a | Toluene | 460 | 8.43 | 1.097 | 300 |
| MeCN | 560 | Cannot be detected | |||
| 6b | Toluene | 430 | 5.12 | 1.128 | 300 |
| MeCN | 565 | 5.94 | 1.117 | 300 | |
| 6c | Toluene | 430 | 2.49 | 1.119 | 300 |
| MeCN | 408 | 7.86 | 0.934 | 300 | |
| 10 | Toluene | 430 | 2.10 | 1.049 | 375 |
| MeCN | 500 | 4.80 | 1.091 | 375 | |
| 7a | Toluene | 471 | 2.06 | 1.080 | 375 |
| MeCN | 539 | 3.13 | 1.198 | ||
| 7b | Toluene | 480, 621 | 1.56, 1.73 | 1.024, 1.044 | 375 |
| MeCN | 525 | 2.87 | 1.011 | 375 | |
| 7c | Toluene | 541 | 4.77 | 1.079 | 375 |
| MeCN | 491 | 2.71 | 1.125 | 375 | |
| 8a | Toluene | 460, 600 | 2.22, 2.95 | 1.082, 1.170 | 375, 375 |
| MeCN | 530 | 2.33 | 1.060 | 375 | |
| 8b | Toluene | 465, 555 | 2.58, 7.01 | 1.093, 1.015 | 375, 375 |
| MeCN | 400, 540 | 1.35, 2.69 | 1.159, 1.090 | 375 | |
| 9 | Toluene | 468 | 3.08 | 1.100 | |
| MeCN | 560 | 3.07 | 1.002 | 300 | |
| 11 | Toluene | 570 | 9.68 | 1.043 | 375 |
| MeCN | Not emissive | ||||
Photoluminescence data for compounds 4–9 and 11 in powder at r. t.
| Compound | λem, nm (Solid) | φ а, % | λem, nm (MeCN) |
|---|---|---|---|
| 4a | 537 | <1 | 541 |
| 4b | 497 | 2 | 545 |
| 4c | 476 | 2 | 490 |
| 5a | 456 | 10 | 535 |
| 5b | 468 | 40 | 535 |
| 5c | 441 | 10 | 490 |
| 6a | 464 | <1 | 560 |
| 6b | 427 | 13 | 420, 560 b |
| 6c | 407 | 9 | 408 |
| 10 | 557 | 1 | 500 |
| 7a | 485, 661 b | <1 | 564 |
| 7b | 474, 598 b | <1 | 525 |
| 7c | 435, 557 b | 2 | 494 |
| 8a | 468, 615 b | <1 | 530 |
| 8b | 451, 596 b | <1 | 400, 540 b |
| 9 | 437, 642 b | <1 | 560 |
| 11 | 610 | 3 | - |
а Absolute quantum yield in solid state was measured by the integrated sphere method. b Major emission maximum is indicated in bold.
Supplementary Materials
The following supporting information can be downloaded at:
References
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; Permyakova, Julia V 1 ; Lipunova, Galina N 3 ; Zhilina, Ekaterina F 3 ; Kim, Grigory A 2
; Slepukhin, Pavel A 2 ; Charushin, Valery N 2
1 Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, Mira St. 19, 620002 Ekaterinburg, Russia
2 Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, Mira St. 19, 620002 Ekaterinburg, Russia; I. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, S. Kovalevskaya Str., 22, 620108 Ekaterinburg, Russia
3 I. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, S. Kovalevskaya Str., 22, 620108 Ekaterinburg, Russia