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Interactions between purine derivatives: Electronic spectral studies. I. Electronic transitions in caffeine monomer and exciton coupling in caffeine dimer
Author(s) -
Kikkert J. N.,
Kelly G. R.,
Kurucsev T.
Publication year - 1973
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1973.360120703
Subject(s) - chemistry , dimer , exciton , absorption spectroscopy , photochemistry , caffeine , monomer , aqueous solution , chemical physics , organic chemistry , polymer , physics , quantum mechanics , medicine , endocrinology
The concentration dependence of the ultraviolet absorption spectrum of aqueous solutions of caffeine has been studied. Individual species spectra have been derived for the monomer, dimer, and tetramer of caffeine. The emission spectrum of caffeine in aqueous solution and the dichroic spectra in oriented poly(vinyl alcohol) and polyethylene films have been measured. The long‐wavelength tail of the absorption spectrum of caffeine in non‐polar environment has been found to incorporate at least one carbonyl(π*, n ) transition. Dichroic spectral data and molecular orbital calculations have been used to assign transition moment directions to the (π*,π) transitions. The lowest energy (π*,π) transition, responsible for the near‐ultraviolet absorption peak in aqueous solution of caffeine, has been used for the study of degenerate exciton interactions in the dimeric species of caffeine. Assuming that the caffeine molecules in the dimer are stacked in parallel planes, theoretical calculations of the ground‐state interactions and of the degenerate exciton interactions have been combined with experimental data and a unique model for the dimer of caffeine has been derived. The transfer rate of energy between the molecules in the dimer is of the order of 10 13 S −1 .