Ultrafast vibrational dephasing dynamics of 9,10-bis(phenylethynyl) anthracene thin film revealed by femtosecond coherent anti-stokes Raman scattering

Ultrafast vibrational dephasing dynamics of 9,10-bis(phenylethynyl)anthracene (BPEA) thin films were revealed by femtosecond coherent anti-stokes Raman scattering spectroscopy (fs-CARS). Dephasing times (T₂) of 2.60, 2.98, 3.72, and 1.64 ps were acquired at 1213, 1300, 1400, and 1478 cm⁻¹ vibrations, respectively. Using steady-state Raman and fast Fourier transform spectra, the dephasing dynamics generated by coherently excited Raman modes 1213 (1478) cm⁻¹ were fitted with 94 (77) cm⁻¹ quantum beat frequencies, with a combination of slow constants τ₁ = 5.92 (2.76) ps and fast constants τ₂ = 1.65 (1.98) ps. These lifetimes could be ascribed to the time scales associated with the structural changes for the C=C Raman modes in the BPEA thin film. Therefore, it is very significant to distinctly understand the underlying ultrafast vibrational dephasing dynamics of the electronic ground state of BPEA caused by vibrational structure changes, which benefits to improve sustainably the molecular device for efficient solar energy conversion.