Solution-State Photophysics Of N-Carbazolyl Benzoate Esters: Dual Emission And Order Of States In Twisted Push-Pull Chromophores

The stepwise photoinduced charge transfer in a series of N-carbazolyl benzoate ester push-pull chromophores has been studied in solution. Dual emission from the locally excited (LE, the lowest-energy singlet excited state of L-1(b) nature localized on the carbazole donor) and the highly polarized, intramolecular charge-transfer states of (pre)-twisted type (TICT states) is observed in non-polar and polar solvents. Ultrafast transient spectroscopy reveals that the excitation into the L-1(b) LE state is followed by rapid (Bps) charge separation into an emissive TICT state. Excitation into the second singlet excited state localized on the carbazole (S2) with L-1(a) nature results in sub-100 fs population of both L-1(b) and TICT states.