Fluorescence lifetime and nonradiative relaxation dynamics of DCM in nonpolar solvent

The nonradiative dynamics of DCM in hexane have been investigated using femtosecond fluorescence up-conversion technique at three excitation wavelengths (400, 445 and 480 nm). The S₁ lifetime was observed to be 9.8 ± 0.5 ps, which is independent of the excitation and the fluorescence wavelengths. The observed S₁ lifetimes of DCJT and DCJTB are slower than those of DCM and DCMB by one order of magnitude, indicating the significance of the twisting motion of the amino group affecting the S₁ nonradiative dynamics. TDDFT calculations suggest that an intersystem crossing is responsible for the observed S₁ dynamics of DCM in nonpolar solvent.