Abstract:
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. Timeresolved
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.
