Multifaceted Ultrafast
Intramolecular Charge Transfer
Dynamics of 4‑(Dimethylamino)benzonitrile (DMABN)
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Abstract
Intramolecular charge transfer (ICT) of DMABN has been
the subject
of extensive investigations. Through the measurements of highly time-resolved
fluorescence spectra (TRFS) over the whole emission region, we have
examined the ICT dynamics of DMABN in acetonitrile free from the solvation
dynamics and vibronic relaxation. The ICT dynamics was found to be
characterized by a broad range of time scales; nearly instantaneous
(<30 fs), 160 fs, and 3.3 ps. TRFS revealed that an ICT state with
partially twisted geometry, ICT(P), is formed within a few hundred
femtoseconds either directly from the initial photoexcited state or
via the locally excited (LE) state. The ICT(P) state undergoes further
relaxation along the intramolecular nuclear coordinate to reach the
twisted ICT (TICT) state with the time constant of 4.8 ps. A conformational
diversity along the rotation of the dimethylamino group was speculated
to account for the observed diffusive dynamics