Coherent and Homogeneous Intramolecular Charge-Transfer Dynamics of 1-tert-Butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6), a Rigid Analogue of DMABN

Abstract

We report the intramolecular charge-transfer (ICT) dynamics of 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6), a planar analogue of 4-(dimethylamino)benzonitrile (DMABN), by using time-resolved fluorescence (TRF) and TRF spectra (TRFS). TRFS allow accurate determination of the ICT dynamics free from the spectral relaxation caused by the solvation and vibronic relaxation. For NTC6 in tetrahydrofuran (THF), the locally excited (LE) state is populated exclusively presumably via a conical intersection from the initial photoexcited S2 (La) state, and the LE state undergoes ICT single exponentially with a time constant of 1.8 ± 0.2 ps. In acetonitrile, however, both LE (22%) and ICT (78%) states are populated from the S2 state, and the population in the LE state undergoes ICT in 800 ± 100 fs. The ICT state undergoes further relaxation in 1.2 ps along the solvation and the intramolecular nuclear coordinates involving the rotation of the amino group to form a twisted ICT state. Coherent nuclear wave packet motions of 130 cm(-1), which can be assigned to the -C≡N group bending mode, were observed in the TRF of the reactant (LE) and product (ICT) states, indicating that the ICT reaction is partially coherent. Compared with DMABN, the ICT dynamics of NTC6 are quite homogeneous, and we speculated on the narrow conformational distribution of NTC6 in the ground state along the rotation of the amino group due to its rigid structure.

Ab Initio Multiple Spawning Photochemical Dynamics of DMABN Using GPUs

“…Experimentally, the gap between the absorption band and the S 1 -LE emission is ~0.7 eV in THF 107 and ~1 eV in vapor phase. 108 The femtosecond time-resolved fluorescence spectrum of DMABN has yet to be measured.…”

Presence of Two Emissive Minima in the Lowest Excited State of a Push–Pull Cationic Dye Unequivocally Proved by Femtosecond Up-Conversion Spectroscopy and Vibronic Quantum-Mechanical Computations

“…It is clear that right after the formation of the fluorescence signal, at 0.5 ps, an apparent isoemissive point is detected in the TRANES at 594 nm, which is retained during the whole decay process. Instead of a simplistic model based on mere solvation, 19,20 this finding promotes the idea of a two-state deactivation [12][13][14]49 where the first emitting state is completely depopulated within the solvation process (3 ps, cf. concentration profile, Supporting Information, section SI.2, Figure SI The Journal of Physical Chemistry B Article of DASPMI: 49 its TRANES evolution showed two well separated emission bands, whose contributions had previously emerged as a clear enlargement of the stationary fluorescence spectrum in highly polar solvents.…”

Excited-state vibrational dynamics toward the polaron in methylammonium lead iodide perovskite

“…Thus, coupled electron–phonon dynamics can be coherently excited on the polaron PES by impulsive excitation, where the associated reorganization energies (λ) and displacements (Δ) determine the polaron formation pathways 35 , 36 . These coherent dynamics have been detected by using femtosecond time-resolved spectroscopies 37 , 38 . For example, Wang et al 39 recently observed a single coherent wave packet oscillating at ~23 cm −1 in a MAPbI 3 film using femtosecond transient absorption.…”