Femtosecond broadband time-resolved fluorescence and transient absorption study of the intramolecular charge transfer state of methyl 4-dimethylaminobenzoate

Abstract

A combined application of femtosecond broadband time-resolved fluorescence (fs-TRF), fluorescence anisotropy (fs-TRFA) and fs to microsecond (μs) transient absorption (TA) have been used to probe directly the dynamics, nature, formation and decay paths of the singlet intramolecular charge transfer ((1)ICT) state of methyl 4-dimethylaminobenzoate (1a) in acetonitrile. The result reveals explicit evidence for a common electronic origin (the L(a) nature) of the (1)ICT state and its precursor the locally excited ((1)LE) state to account jointly for the dual florescence known to this system. It also shows that the ICT reaction from the (1)LE to (1)ICT state occurs with time constant of ~0.8 ps and the (1)ICT state formed decays with a ~1.9 ns time constant leading mainly to a ππ* natured triplet state ((3)T(1)). The (3)T(1) then relaxes with a ~4 μs lifetime under deoxygenated condition resulting in full recovery of the ground state (S(0)). As a case study, this work contributes novel experimental data for improved understanding of the mechanism of ICT reaction; it also reveals a distinct deactivation pattern for this prototype para-amino substituted aromatic carbonyl compound in acetonitrile.

Comprehensive investigation of the excited-state dynamics of push–pull triphenylamine dyes as models for photonic applications

“…The same conclusion was reported for methyl-4-dimethylaminobenzoate (DMABM) for which the k 0 F (ICT) is B25 times smaller than k 0 F (LE). 55 In this respect, 2 differs clearly from DMABN and DMABM by the high fluorescence quantum yield in both polar and nonpolar solvents (F F = 0.31 in MeCN and EtOH, 0.42 in HEX) and an ICT k 0 F only B3 times smaller than the LE k 0 F (Table 2). The strongly emissive character of the S 1 (ICT) state of 2 may exclude the presence of such an important p-electronic decoupling between the electron-donor and -acceptor subunits, which would not be consistent with a perpendicular conformation.…”

“…In support of this conclusion, the red-shift of the ICT emission relative to the pp* emission in MeCN is much smaller for 2 (B4400 cm À1 ) than for DMABN (B7400 cm À1 ) 42 and DMABM (B8000 cm À1 ). 55 This indicates that the charge separation and conformational change accompanying the ICT reaction are smaller in the case of 2. Such attenuation of the ICT strength in 2 might be due to the presence of the biphenyl groups that, as remarked above, exert a charge withdrawing effect that does not exist in DMABN and DMABM.…”

Spectral broadening induced by intense ultra-short pulse in 4H–SiC crystals

“…[8] The frequency broadening or continuum spectral pulses with fs duration as a tunable probe light source are useful in characterizing pump-probe spectroscopy of ultrafast process. [9][10][11][12][13] So far, it is usually generated by using crystals such as fused silica, [4] BaF 2 , [5] and CaF 2 . [6] But these crystals often suffer from damage associated with the self-focusing effect due to their low damage thresholds.…”

Intramolecular charge transfer interactions and molecular order of rod like mesogens

“…5 Molecular materials with dimethylamino group have attracted considerable attention due to their fundamental importance in photo-induced intramolecular charge transfer and their applications in sunscreens. 9 Of particular interest is on 4-dimethylaminobenzoates in which dimethylamino acts as a donor while the benzoate moiety as acceptor. 10 As a result these molecular systems have been used as important model molecules in probing many aspects of excited intramolecular charge transfer state.…”