Excited-state properties of trichromophoric dye molecules

A new time-resolved laser-scanning-microscopy technique is used to measure the excited-state properties of two structural related rhodamine dyes and their 2,5-diphenyloxazole (PPO) derivates. The PPO antennas are separated by methylene bridges from the rhodamine chromophore. An efficient energy transfer from the excited PPO to the rhodamine chromophore is observed. Neither the fluorescence lifetime nor the fluorescence quantum yield of the rhodamine chromophore is affected by the PPO antennas. In contrast, the presence of the PPO antennas significantly influences the intersystem-crossing rate constant as well as the triplet-triplet and excited singlet absorption spectra of the rhodamine chromophore. This observation is clearly in contradiction to the simple model of separated individual chromophores, which is often used to describe multichromophoric dyes.