Femtosecond Spectroscopy and Dynamics of the Azulenylosquaric Dye, a Near-infrared Nonfluorogenic Quencher

摘要

An azulenylosquaric dye (ASQ) has been synthesized to investigate its associated photophysical properties. ASQ is essentially nonluminescent (Φ_f < 3 x 10~(-6)) in any solvent despite its very high absorption extinction coefficient (760 nm, ε ～ 8.2 x 10~4 M~(-1) cm~(-1) in methanol). Femtosecond fluorescence upconversion, anisotropy kinetics and transient absorption experiments, in combination with the theoretical time-dependent DFT approach, leads us to conclude that the 760 nm absorption is ascribed to the fully allowed S_0 → S_n (n ≥ 2) transition. The observed < 130 fs decay component is attributed to the S_n → S_1 internal conversion, while the S_1 → S_0, with a slower radiative decay time (> 233 ns) undergoes a dominant radiationless deactivation process (710 ± 70 fs) possibly governed by strong interaction between S_1 and S_0 potential energy surfaces.