Optical Investigation of Self-Aggregation of a Tetrazole-Substituted Diphenylacetylene Derivative: Steady and Excited State Dynamics in Solid and Solution State

Slow crystallization and fast precipitation of a tetrazole-substituted diphenylacetylene derivative (MPT) led to formation of solids with significantly different photoluminescence efficiencies of 0.06 and 0.33, respectively. A detailed study of the photophysical properties of solutions of MPT as a function of concentration and temperature indicated that the extent of formation of J- and H-aggregates played a significant role in determining the luminescence properties of these materials. Time-resolved emission spectroscopy showed that the lifetime of emission arising from the aggregated species was significantly higher than that of the monomer species. The long-lived emission might be due to the formation of excimer arising from the excitation of ground state J- and H-aggregates. The higher quantum yield of fluorescence in the solids obtained by fast precipitation could be attributed to the presence of increased amounts of J-aggregates similar to that observed in highly concentrated solutions (≥ 4.2 × 10–4 M). The photophysical studies of MPT in various concentrations indicate that J-aggregates are significantly more fluorescent than the H-aggregates. Transient absorption spectra measured by nanosecond laser flash photolysis indicated the formation of a triplet excited state with an absorption maximum of ∼490 nm and a quantum yield of 0.61.