Rodlike Molecules and Singlet Energy Transfer1,2

• Published in: Journal of organic chemistry 2000-11, Vol.65 (23), p.7740-7746
• Main Authors: Zimmerman, Howard E, Lapin, Yuri A, Nesterov, Evgueni E, Sereda, Grigoriy A
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo0003145

In continuing our investigations on rodlike molecules composed of bicyclo[2.2.2]octane units, we studied the effect of interposing a single aromatic ring in the rod. Thus, two [3]-rods were synthesized with the two outer units being bicyclooctyls, the central unit being benzenoid, and with one terminal unit bearing an α-naphthyl moiety and the other terminus bearing an acetyl or benzoyl group. Excitation of the α-naphthyl group led to fluorescence emission by both the naphthyl and the acetyl units. However, compared to the [1]- and [2]-rods previously studied, transmission of singlet excitation proved to be less efficient as determined by the fluorescence emission and also by the singlet lifetimes obtained from single photon counting measurement. Transmission to the benzoyl group proved more rapid than to the acetyl moiety. In assessing the factors controlling energy transmission, Δ-density determinations were employed to describe the distribution of electronic excitation in such systems. It was observed that despite most of the energy being located in the terminal chromophores, some is distributed in the bicyclooctyl units. The extent of this distribution provides a guide to the facility of through-bond energy transfer. Evidence is presented that energy transfer in the short rods is mainly through-bond while in the longer rods Förster through-space transfer is involved.