Conformation-Dependent Photophysics of Bifunctional Hydrogen Bond Donor/Acceptor Molecules
M. Kijaka, b, I. Petkovaa, c, M. Toczeka, G. Wiosna-Sałygaa, A. Zielińskaa, J. Herbicha, b, R.P. Thummeld and J. Waluka, b
aInstitute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw, Poland
bFaculty of Mathematics and Natural Sciences, College of Science Cardinal Stefan Wyszyński University, Dewajtis 5, 01-815 Warsaw, Poland
cInstitute of Organic Chemistry, Bulgarian Academy of Sciences Akad. G. Bontchev bl. IX, Sofia 1113, Bulgaria
dDepartment of Chemistry, University of Houston, Houston TX 77204-5003, USA
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Received: 26 10 2007;
A series of heteroazaaromatic molecules possessing both a hydrogen bond donor and acceptor groups linked by a single bond was studied using electronic absorption and fluorescence techniques, combined with quantum-chemical calculations. Fluorescence lifetimes and quantum yields strongly depend on the solvent. Double exponential decays are observed in alcohols. This was interpreted in terms of alcohol-induced syn-anti rotamerization in the ground electronic state. The driving force for the conformational change is provided by two factors: (a) solvent polarity increase; (b) the formation of two separate hydrogen bonds in the anti species. In the syn structure, formation of cyclic hydrogen bonds leads to rapid depopulation of the lowest excited singlet state via two competing mechanisms: proton transfer and enhanced internal conversion. The experimental results are rationalized by calculations which include specific and nonspecific solvent effects.
DOI: 10.12693/APhysPolA.112.S-105
PACS numbers: 33.15.-e, 02.70.-c