Excited-state vibrational relaxation and deactivation dynamics of trans-4-(N,N-dimethylamino)-4′-nitrostilbene in nonpolar solvents studied by ultrafast time-resolved broadband fluorescence spectroscopy

• Vibrational relaxation of DMANS S1 state proceeds in multiple stages within ∼15 ps.
• Oscillatory fluorescence was observed and assigned to a coherent vibrational motion.
• Total fluorescence intensity decay agrees with a mixed triplet–single deactivation mechanism.

The excited-state relaxation dynamics of trans-4-(N,N-dimethylamino)-4′-nitrostilbene excited to the first absorption band in nonpolar solvents (cyclohexane and n-hexadecane) has been studied with ultrafast time-resolved broadband fluorescence spectroscopy. The temporal evolution of the time-resolved fluorescence spectra and bandwidth narrowing reveal a multiple-stage vibrational relaxation within ∼15 ps followed by slower excited-state deactivation steps (80 and 950 ps in cyclohexane). In addition, an oscillatory fluorescence with a period of about 1.1 ps was observed and attributed to the coherent vibrational motion of the nitrophenyl/aminophenyl torsion that modulates the early-time fluorescence spectra. The decay of the total fluorescence intensity with cubic frequency correction was found to be consistent with a competitive triplet–single deactivation mechanism.

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