INTRAMOLECULAR NAPHTHALENE TRIPLET EXCIMERS IN SOLUTIONS OF PHOSPHAZENE COPOLYMERS

Phosphorescence and transient absorption spectra of poly[bis(beta-naphthoxy)phosphazene] and of its model compound, hexakis(beta-naphthoxy)cyclophosphazene, have been found to be significantly different in both 2-methyltetrahydrofuran/methylene chloride fluid solutions and rigid matrices. The spectroscopic characteristics of the model compound closely resemble those of the naphthalene chromophore while, on the contrary, no naphthalenic triplet-triplet absorption or phosphorescence appears in the polymer. Population of the naphthalene triplet was achieved by energy transfer in a series of phosphazene copolymers containing benzophenone and napthalene in variable amounts. Copolymer samples containing high naphthalene percentages show a peculiar red-shifted and broadened phosphorescence with respect to copolymers containing low naphthalene content, which exhibit the typical naphthalene bands. Transient absorption experiments have shown that a broad absorption band around 500 nm is due to the same state responsible for this anomalous phosphorescence. On the basis of close similarities with literature data and of the effect of naphthalene crowding on the formation of the species, this is identified as a naphthalenic triplet excimeric state.