Comparative theoretical study of rotamerism and excited state intramolecular proton transfer of 2-(2'-hydroxyphenyl)benzimidazole, 2-(2'-hydroxyphenyl)imidazo[4,5-b]pyridine, 2-(2'-hydroxyphenyl)imidazo[4,5-c] pyridine and 8-(2'-hydroxyphenyl)purine

Francis A S Chipem, G Krishnamoorthy
Journal of Physical Chemistry. A 2009 November 5, 113 (44): 12063-70
The effect of nitrogen substitution in the benzene ring of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) on the photophysics and rotamerization were examined theoretically by a comparative study of HPBI with 2-(2'-hydroxyphenyl)imidazo[4,5-b]pyridine (HPIP-b), 2-(2'-hydroxyphenyl)imidazo[4,5-c]pyridine (HPIP-c), and 8-(2'-hydroxyphenyl)purine (HPP). Density functional theory (DFT) was used for ground state calculations. Restricted configuration interaction singles (RCIS) combined time dependent DFT (TDDFT) was used for excited state calculations. The calculations reveal in the ground state all of the molecules have two stable rotameric forms, but their relative population is strongly affected by nitrogen substitution. The excitation and emission bands have been calculated theoretically for the rotamers and tautomers. Fluorescence emission and excitation spectra were recorded for HPBI in dioxane and compared with the theoretical results. Theoretical excitation and emission data are in good agreement with the available experimental data. The potential energy surface simulated for the proton transfer processes reflect that it is not favorable in S(0) state, but it is feasible in S(1) state in all of the molecules. Except in HPIP-b, HPIP-b', and HPP', in all other nitrogen substituted molecules, the energy difference between the keto and enol form along the excited state proton transfer coordinates decreases compared to that in HPBI. The study also reveals that torsional relaxation of tautomer to twisted state competes with radiative transitions and leads to fluorescence quenching. Nitrogen substitution enhances this torsional induced nonradiative process and it follows the order HPBI < HPIP-b < HPIP-c < HPP.

Full Text Links

Find Full Text Links for this Article


You are not logged in. Sign Up or Log In to join the discussion.

Related Papers

Remove bar
Read by QxMD icon Read

Save your favorite articles in one place with a free QxMD account.


Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"