Research of electronic absorption spectra of benzazols derivatives by ab initio calculations

Abstract

Using the method of density functional theory in approximating B3LYPwith the basis set 6-31G* the computations of structures and UV-vis spectra (TDDFT method) of benzazols derivatives were performed. The comparison of estimated electron spectra with the observed ones was made indicating good agreement of theoretically obtained results with experiment. Moreover these compounds have distinctive spectralluminescent properties (large stokes shift) because of intramolecular proton transfer in excited state.

Electronic and photophysical properties of 2-(2′-hydroxyphenyl)benzoxazole and its derivatives enhancing in the excited-state intramolecular proton transfer processes: A TD-DFT study on substitution effect

“…While, the electron donor shows a small contribution of mesomeric effect leading to π-electron density disappearance. Our computed results of m-MeHBO, MHBO, and CNHBO are in good agreement with experiment data [29,31,36]. For 6-position substitution, electron donors (HBOMe and HBOM) show blueshifted emission with maxima at 475 and 466 nm, respectively while electron acceptors (HBOF, HBOCl, HBOA, and HBOE) show redshifted emission with maxima at 482, 487, 644, and 563 nm, respectively.…”

“…Similarly, strong electron withdrawing (-CN) group of CNHBO shows absorption maxima at 333 nm and 296 nm with f values of 0.572 and 0.295, respectively. A large redshifted absorption compared to HBO, observed in CNHBO corresponding to the lower energy gap than that of HBO, agrees well with experiments [29]. The slight Table 2 Relative energies (kcal mol À 1 ) and selected structural parameters (Å and deg) from optimized structures of HBO and its derivatives computed at B3LYP/6-311 þG* level (in gas phase In addition, electron donor substituted on 4′-position and electron acceptor substituted on 6-position of m-MeHBON also give redshifted absorption with peak at 337 nm (f¼ 0.724) for π-π* and n-π* transition (very small f).…”

“…Moreover, Seo et al [36] reported that the emission of HBO derivative having methoxy (-OCH 3 ) as an electron donor on 4′-position of the phenol moiety in non-polar solvent gave the keto emission peak at about 466 nm (blueshifted emission relative to HBO). The keto emission of HBO derivative having cyano (-CN) as an electron acceptor at the same position of the phenol moiety also was blueshifted $ 10 nm (compared to HBO at 506 nm in solid state) as reported by Irgibaeva et al [29]. In addition, Seo et al [36] studied on HBO having aldehyde and ester group (-CHO (510 nm) and -COOC 2 H 5 (480 nm)) substituted at this position.…”

“…The photophysics of HBO as the parent compound in our present work has been widely studied experimentally [1,2,5,7,9,18,[21][22][23][24] and theoretically [25][26][27][28][29][30][31][32][33][34][35] because of its structural simplicity and easily chemical modification. Thus, its derivatives [14,25,31,[36][37][38] have also been increasingly investigated both in experiment and theoretical studies.…”

“…The following substituents placed to two positions: (i) 4′-position, (ii) 6-position and (iii) both 4′-and 6-position of HBO to give 10 different HBO derivatives as depicted in Fig. 1 have been studied namely (i) 2-(2′-hydroxy-4′-methylphenyl)benzoxazole (m-MeHBO) [25,40], 2-(2′-hydroxy-4′-methoxyphenyl)benzoxazole (MHBO) [31,36], 2-(2′-hydroxy-4′-cyanophenyl)benzoxazole (CNHBO) [29], (ii) 2-(2′-hydroxyphenyl)-6-methylbenzoxazole (HBOMe) [41], 2-(2′-hydroxyphenyl)-6-methoxybenzoxazole (HBOM), 2-(2′-hydroxyphenyl)-6-fluorobenzoxazole (HBOF), 2-(2′-hydroxyphenyl)-6-chlorobenzoxazole (HBOCl) [41], 2-(2′-hydroxyphenyl)-6-cabaldehydebenzoxazole (HBOA) [36] and 2-(2′-hydroxyphenyl)benzoxazole-6-carboxylic acid ethyl ester (HBOE) [36], and (iii) 2-(2′-hydroxy-4′-methylphenyl)-6-nitrobenzoxazole (m-MeHBON).…”