Jet-Cooled Fluorescence Excitation Spectra and Potential Energy Functions for the Carbonyl-Wagging and Ring-Puckering Vibrations of Bicyclo[3.1.0]hexan-3-one in Its S1(n,.pi.) Electronic Excited State

1995 ◽  
Vol 99 (30) ◽  
pp. 11640-11643 ◽  
Author(s):  
Whe-Yi Chiang ◽  
Jaan Laane
Keyword(s):  
Excited State ◽  
Potential Energy ◽  
Excitation Spectra ◽  
Fluorescence Excitation ◽  
Energy Functions ◽  
Potential Energy Functions ◽  
Electronic Excited State ◽  
Fluorescence Excitation Spectra ◽  
Ring Puckering

Excited state intramolecular proton transfer in 2-(2'-hydroxyphenyl)-1H-naphth-[2,3-d]-imidazole: effects of solvents and pH

2000 ◽  
Vol 78 (2) ◽  
pp. 191-205 ◽  
Author(s):  
Somes K Das ◽  
G Krishnamoorthy ◽  
Sneh K Dogra
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Radiative Decay ◽  
Intramolecular Proton Transfer ◽  
Normal Band ◽  
Am1 Method ◽  
Excitation Spectra ◽  
Fluorescence Excitation ◽  
Protic Solvents ◽  
Fluorescence Excitation Spectra

The solvent dependent study of absorption, fluorescence, and fluorescence excitation spectra of 2-(2'-hydroxyphenyl)-1H-naphth-[2,3-d]-imidazole (HPNI) have indicated the presence of different rotamers and tautomers in the So and S1 states. Similarity of the absorption and fluorescence spectra of HPNI in protic solvents with those of 2-(2'-methoxyphenyl)-1H-naphth-[2,3-d]-imidazole (MPNI) suggests that the normal emission is observed from the rotamers 2 and 4, whereas the tautomer emission is observed from the tautomer 3, formed by the excited state intramolecular proton transfer (ESIPT) in the rotamer 1 (Scheme 1). Ground state geometries of rotamers 1, 2, and the tautomer 3 were optimized using AM1 method. The results show that the rotamer 2 is the most stable and its stability further increases in polar and protic solvents due to the dipolar solvation interaction. The increase in the fluorescence quantum yield of the normal band when methanol or water is added to dioxane is due to: (i) the formation of rotamer 4, where ESIPT is not possible and (ii) the decrease in the rate of non-radiative decay process. Very large red shifted fluorescence bands of the monocations of HPNI and MPNI in different solvents have been assigned to the charge transfer band.Key words: 2-(2'-hydroxyphenyl)-1H-naphth-[2,3-d]-imidazole, ESIPT, prototropic reactions, fluorescence, 2-(2'-methoxyphenyl)-1H-naphth-[2,3-d]-imidazole.

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