Femtosecond dynamics of intramolecular charge transfer in 4-dimethylamino-4′-cyanostilbene in polar solvents

Abstract

The femtosecond dynamics of 4-(N,N-dimethylamino)-4'-cyanostilbene (DCS) in acetonitrile and methanol solvent was studied by fluorescence upconversion and pump-probe absorption spectroscopy. The spectral evolution observed provides strong evidence for a fast internal charge-transfer (CT) process dominating the dynamics in the first few picoseconds, while Stokes shift dynamics seem to play only a minor role. The initially excited state seems to have already a large amount of CT character, in line with observations in jet-cooled DCS-solvent clusters. The non-exponential CT-state formation contains components significantly faster than longitudinal dielectric relaxation rates in the solvents studied, indicating a possible contribution by high-frequency vibrational modes.

Femtosecond luminescence dynamics in a nonlinear optical organic dendrimer

“…11 This model is adequate for the formation of excited states with conformational changes involving the twisting of one of the single bonds ͑''twisted intermolecular charge transfer'' TICT states͒, 11 as well as for solvent relaxation processes. 16 In our results, the emission wavelength dependence of the short lifetime component and the contribution of the long-lived component are in accordance with the formation of two fluorescence states. Also, the polarity dependence of the short lifetime component as well as the long-lived component contribution do not contradict this model.…”

“…The fluorescence decay pattern ͑rise time plus emission-wavelength-dependent contribution of the long-lived component͒ seen for the CZD4SNC2 dendrimer is typical of two-component ͑dual͒ fluorescence. [11][12][13]16,17 The presence of a blue shoulder at about 485 nm in the steady-state fluorescence spectrum shown in Fig. 2 also supports this dual fluorescence model.…”

“…2 also supports this dual fluorescence model. Generally, dual ͑multiple͒ fluorescence could be associated with either solvent rearrangement 16,18 or photoinduced solute conformational changes. 11,13,17 It might also be suggested that the long-lived decay and the rise-time components could be connected with the formation of aggregates such as excimers or exciplexes.…”

“…11,16 Such a dependence of the fluorescence kinetics on the solvent polarity at particular emission wavelengths could be the result of a solvatochromic shift of the fluorescence line, which is quite strongly dependent on polarity for donoracceptor systems like NAS. [11][12][13]16 However, a comparison of the fluorescence dynamics at the fluorescence maxima also showed a dependence on polarity ͑the same trend as for fixed emission wavelength͒. This suggests that the dynamics of the relaxed state formation process are also polarity dependent, and indicates that observed solvent-dependent dynamics are not directed by the solvatochromic shift.…”

Early Excited State Dynamics of 6-Styryl-Substituted Pyrylium Salts Exhibiting Dual Fluorescence

“…Most observations of dual emission are due to molecules experiencing a chemical process, such as electron or proton transfer, [49][50][51][52][53] or a substantial conformational change on the excited-state surface. 54,55 It should be noted that in these cases, the excited state responsible for the low energy fluorescence cannot be directly populated upon optical excitation.…”