Multifaceted Ultrafast Intramolecular Charge Transfer Dynamics of 4‑(Dimethylamino)benzonitrile (DMABN)

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 117; no. 2; pp. 370 - 377
• Main Authors: Park, Myeongkee, Kim, Chul Hoon, Joo, Taiha
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 17.01.2013
• Subjects: Acetonitrile; Atomic and molecular physics; Charge transfer; Diffusion; Dynamics; Exact sciences and technology; Femtosecond; Fluorescence and phosphorescence spectra; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Molecular properties and interactions with photons; Physical chemistry; Physics; Solvation; Spectral emissivity; Fluorescence spectrum; Chemical solution; Benzenic compound; fs range; Nitriles; Excited states; Intramolecular charge transfer; Organic compounds; Ultrafast process
• ISSN: 1089-5639; 1520-5215; 1520-5215
• DOI: 10.1021/jp310842z

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.