This article presents a comprehensive theoretical investigation of excited state intramolecular proton transfer (ESIPT) for some newly-designed diphenylethylene derivatives containing 2-(2-hydroxy-phenyl)-benzotriazole moiety with various substituted groups. The calculation shows the structural parameters and Mulliken charges of phototautomers enol (E) and keto (K) of these compounds exhibit no or tiny changes from S(0) to S(1). The calculated results suggest that HOMO and LUMO + 1 of the compounds displays excellent overlapping nature, and thus the absorption and emission could be from the electron transition of HOMO→LUMO + 1. The electron density distribution in the frontier orbital of E and K are influenced remarkably by various substituted groups in S(0) and S(1) states. Electron density distribution deficiency in 2-(2-hydroxy-phenyl)-benzotriazole part is observed in L + 1 for these derivatives. The calculation also suggests the potential energy curves of ESIPT are shown to be a strong relationship with electron donor-acceptor groups. The absorption spectra, normal emission spectra and ESIPT spectra of the derivatives were also calculated.
[Show abstract][Hide abstract] ABSTRACT: ESIPT inspired fluorescent 2-(4-benzo[d]oxazol-2-yl)naphtho[1,2-d]oxazol-2-yl)phenol was synthesized from 1-amino-3-(1,3-benzoxazol-2-yl)naphthalen-2-ol. Photophysical behavior of the synthesized compound was studied using UV–visible and fluorescence spectroscopy in polar and non-polar solvents. The synthesized naphthoxazolyl benzoxazole is fluorescent and very sensitive to the micro-environment. It shows a single absorption and dual emission in non-polar solvents with large Stokes shift originating from Excited State Intramolecular Proton Transfer while in polar solvents only a single short wavelength emission is observed. Experimental absorption and emission wavelengths are in good agreement with those predicted using the Time-Dependent Density Functional Theory (TD-DFT) [B3LYP/6-31G(d)]. The largest wavelength difference between the experimental and computed absorption maxima was 16 nm (acetonitrile) and 7 nm (ethyl acetate, THF, and 1,4-dioxane) in the short and long wavelength regions, respectively. A largest difference of 25 nm was observed for the short wavelength emission in DMF and 22 nm for the longer wavelength emission in chloroform.
[Show abstract][Hide abstract] ABSTRACT: The excited-state intramolecular proton transfer (ESIPT) fluorescence of the synthesised 2-(1,3-benzothiazol-2-yl)-5-(N,N- diethylamino)phenol (1) was studied using spectroscopic and theoretical methods. The changes in the electronic transition, energy levels, and orbital diagrams were investigated using the ab initio molecular orbital computation [B3LYP/6-31G(d)]. Compound (1) is fluorescent; it shows a single absorption and dual emission in solvents of different polarities. Experimental absorption and emission wavelengths are in good agreement with those predicted using the Time-Dependent Density Functional Theory [TD-B3LYP/6-31G(d)]. The photophysical properties of compound (1) are compared with benzoxazole and benzimidazole analogues.
[Show abstract][Hide abstract] ABSTRACT: A total number of nineteen 2-arylbenzotriazoles related to the UV absorber Tinuvin P have been studied. Moreover, besides those bearing a 2′-hydroxy substituent, known to experience ESIPT (Excited-State Intramolecular Proton Transfer), we have also prepared three compounds having another ortho-hydroxy group at position 6′. The X-ray molecular structures of five key representatives have been determined and some important features related to their behavior discussed on the basis of solution and solid-state NMR, as well as B3LYP/6-311++G(d,p) computational results.
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