INFLUENCE OF THE N-SUBSTITUENT ON THE PHOTOPHYSICAL PROPERTIES OF OXACARBOCYANINES IN SOLUTION

The influence of the rotational volume and redox properties of the N-s ubstituents on the fluorescence spectra and decays of oxacarbocyanine dyes were investigated as function of the solvent polarity and/or pola risability. While alkyl and alkylbenzene side chains give rise to one- exponential fluorescence decay, the presence of a butylnaphthyl substi tuent induces a bi-exponential fluorescence decay in solvents with low polarisability and/or polarity. This was attributed to a conformation where the naphthyl moieties form a ground state dimer. With alkylpyre nyl substituents the fluorescence decay becomes bi-exponential due to the occurrence of a reversible intramolecular electron transfer.