Photo-induced intramolecular charge transfer and internal conversion in molecules with a small energy gap between S1 and S2. Dynamics and structure

Intramolecular Charge Transfer with N,N-Dialkyl-4-(Trifluoromethyl)anilines and 4-(Dimethylamino)benzonitrile in Polar Solvents. Investigation of the Excitation Wavelength Dependence of the Reaction Pathway

“…1 and Table I). The results with DMABN and DMCF3 show that ∆E(S 1 , S 2 ) is the determining factor for the occurrence of ICT and dual fluorescence with D/A molecules, in accordance with the PICT approach [4,5,8,9].…”

“…According to the present authors and previous publications, internal conversion (IC) follows excitation and the ICT reaction then proceeds from the relaxed locally excited (LE) state as the precursor, in an adiabatic S-41 reaction pathway [4,5,[8][9][10]]. An alternative mechanism was proposed by Fuß and co-workers on the basis of their femtosecond nonresonant multiphoton ionization experiments with DMABN and 1-methyl-6-cyano-1,2,3,4-tetrahydroquinoline (NMC6) in the gas phase [11,12].…”

“…This means that the energy gap ∆E(S 1 , S 2 ) of DMABN decreases when the solvent polarity becomes larger (Table I) [17,18]. As emphasized in the PICT model [4,5,8,9], this decrease in ∆E(S 1 , S 2 ) leads to the appearance of an ICT fluorescence band to the red of the LE emission. Whereas there is no indication of the presence of ICT fluorescence for DMABN in n-hexane (Fig.…”

“…Whereas there is no indication of the presence of ICT fluorescence for DMABN in n-hexane (Fig. 1a) [3,9,10,23] ICT emission is clearly present in DEE and has become the major fluorescence band in MeCN [3,9,10,24,25], with ICT/LE fluorescence quantum yield ratios Φ (ICT)/Φ(LE) of 0.30 in DEE and 39.5 in MeCN (Table I).…”

“…For this state, two models making a statement on the twist angle of the amino group with respect to the phenyl ring have survived the debate since the discovery [1,2] of the dual fluorescence of DMABN and its derivatives in 1959: the TICT (twisted ICT) and PICT (planar ICT) models [3][4][5]. In the TICT structure, a perpendicular, i.e., fully twisted (90 • ) [3,6], amino group is assumed [7], whereas in the PICT model [4,5,8,9] such a 90…”