DEACTIVATION OF EXCITED XANTHENE DYE DIMERS

Photoacoustic calorimetry was used to investigate the deactivation of electronically excited dimers of rhodamine B and eosin Y in water. Temperature dependence experiments were used to evaluate a possible photodissociative deactivation path, which should be accompanied by chemical volume changes. The quantitative evaluation demonstrates that photodissociation plays no role. Radiationless deactivation occurs for both dimers with unit quantum yield. Since the entire absorbed photon energy is released very rapidly as heat, deactivation occurs by internal conversion but not by intersystem crossing.