On the Photophysics of Polyenes. 1. Bathochromic Shifts in Their 1Ag → 1Bu Electronic Transitions Caused by the Polarizability of the Medium

As shown in this study, the solvatochromic behavior of polyenes depends exclusively on the polarizability of the medium and, even more interestingly, their solvatochromism increases markedly with increasing length of the polyene chain. By virtue of the electronic nature of the interaction of polyenes with the medium, their solvatochromic response to a polarizability change is instantaneous, making these compounds extremely effective polarizability probes for molecular environments. The extreme sensitivity of polyenes to the polarizability of their environment is consistent with the fact that changes in molecular architecture such as those occurring in photosynthetic systems can give rise to polarizability gradients resulting in red shifts in the 1Ag --> 1Bu transition, thereby opening up new channels directing the energy transfer involved to energy trapping sites in such systems.