Sub-picosecond fluorescence evolution of amino-cyano-stilbenes in methanol: polar solvation obeys continuum theory without evidence of twisting

Abstract

The spectral evolution of fluorescence from 4-(dimethylamino)-4'-cyanostilbene (DCS) in methanol, and of two derivatives bearing either the anilino (ACS) or the julolidino (JCS) moiety, was measured by optical Kerr-gating with a time resolution of 0.35 ps. A special thin Glan polariser in the Kerr shutter allows high contrast without unnecessarily increasing the group delay dispersion. The emission band may thus be gated and observed even with highly fluorescent samples. The spectral dynamics consists of a continuous red-shift and narrowing with similar relaxation behavior throughout, i.e. between these two observables and the three compounds. This suggests that polar solvation is the common cause for spectral relaxation after 0.2 ps. The continuum model describes the dynamic Stokes shift quantitatively. Contrary to previous reports we do not find a temporary isosbestic point in the fluorescence of JCS, nor is there evidence for a dependence on anilino substituents. The crystal structures of DCS and JCS are provided.

Synthesis, Photophysics and Nonlinear Optical Properties of Stilbenoid Pyrimidine‐Based Dyes Bearing Methylenepyran Donor Groups

“…[37] Even though the solvatochromic measurements are performed over a limited range of the solvent polarity scale, the dipole moment change (µ ge ) can be estimated to 15 ± 1 D and 19 ± 2 D for chromophores 3 and 5 respectively. Such values are of the same magnitude as those obtained for 'push-pull' trans-stilbenes such as 4-cyano-4'-dimethylaminostilbene [38] (~ 15 D) or 4-methoxy-4'-nitrostilbenes [33], [39] (~ 23 D) and therefore illustrate the significant CT character of the emitting states.…”

Femtosecond broadband fluorescence upconversion spectroscopy: Spectral coverage versus efficiency

“…In initial work, a difficulty was presented by the limited extinction ratio of a polarizing wire grid, 10,11 but this drawback has since been removed by the use of a thin Glan polarizer. 12,13 Only the achievable width ∆t of the instrumental response function is larger compared to other methods, when the optimal Kerr medium (benzene) is used.…”

“…Here we test that principle for broadband fluorescence upconversion spectroscopy (FLUPS). [4][5][6][7] Fluorescence gating has been performed with a Kerr shutter, [8][9][10][11][12][13][14][15] by non-collinear optical parametric amplification [16][17][18][19][20] or by diffraction from a transient grating, 21 in addition to broadband upconversion schemes. [4][5][6][7][22][23][24][25] Here we consider only reports where spontaneous emission from molecular or similar sources is gated, dispersed, and registered simultaneously at all relevant wavelengths with a view to obtain true molecular spectra.…”

Donor-Acceptor Conjugated Linear Polyenes: A Study of Excited State Intramolecular Charge Transfer, Photoisomerization and Fluorescence Probe Properties

“…Time-resolved fluorescence studies of DCS type systems indicate presence of at least two species in their excited state. The dual fluorescence in such systems has been attributed to the twist over the single bond attached to aryl and donor Ar-N group (single bond attached to NH 2 ) [40,42]. Our group has found solvent dependent dual fluorescence in cyano-and methoxysubstituted stilbenes [39,40] (Fig.…”

“…It has been shown that N,N-dimethylamino-p-cyano stilbene (DCS) and its derivatives exhibits dual fluorescence due to the existence of LE and CT excited states [33][34][35][36][37][38][39][40][41][42]. Such systems show large solvatochromic, red-shifted fluorescence with high fluorescence quantum yield (Φ f ).…”