Interactions between purine derivatives: Electronic spectral studies. I. Electronic transitions in caffeine monomer and exciton coupling in caffeine dimer

✍ Scribed by J. N. Kikkert; G. R. Kelly; T. Kurucsev

• Book ID: 102761438
• Publisher: Wiley (John Wiley & Sons)
• Year: 1973
• Tongue: English
• Weight: 966 KB
• Volume: 12
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1973.360120703

✦ Synopsis

Abstract

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^.