Dual Fluorescence and Excited-State Structural Relaxations in Donor−Acceptor Stilbenes

Abstract

The time-resolved fluorescence behavior of two derivatives of 4-(dimethylamino)-4′-cyanostilbene (DCS) bearing a more voluminous (JCS) and less voluminous anilino group (ACS) was investigated in ethanol by reconstructing the emission spectra using picosecond time-resolved single-photon-counting technique. For JCS, these spectra exhibit a temporary isosbestic point, a clear indication of level dynamics between two emitting excited singlet states (LE and CT). Kinetic evaluation yielded a precursor-successor relationship between LE and CT and CT formation time constants of 4 ps for ACS and 8 ps for JCS. This slowing of the reaction for the compound with the larger volume of the donor moiety supports the assumption of a twisting mechanism being a major component of the reaction coordinate. An additional transient red shift of the CT band is observed for both compounds and follows the relatively slow solvation dynamics (ethanol).

Luminescent and Electronic Properties of Stilbenoid NCN‐Pincer PtII Compounds

“…For 6, indeed a decrease in k nr with increasing solvent polarity is found. This is in agreement with what was found for JCS, [83,84] for which the yield of the nonradiative decay also decreases with increasing solvent polarity.…”

“…Both E* and A* are highly polar, with an increased dipole moment for A*; P* has weak or nonpolar properties. [83] Therefore, an increase in the solvent polarity stabilizes E* and A*, and to a much lesser extent P*. As a result, the nonradiative decay, which is governed by the access to P*, becomes less important.…”

Quenching of fluorescence for fluoro derivatives of the laser dye DCM in polar solutions

“…Compounds in which rotation of molecular moieties about single and double bonds is possible in nonpolar solvents generally have low fluorescence quantum yield Φ fl [14], and quenching is due to adiabatic transitions to a low-lying non-fluorescent "phantom" state "twisted" about the double bond [13,14]. For model compounds in which internal rotation about the double bond is chemically ruled out [14,15] and for "rigid" coumarin dyes [16-18], a high fluorescence quantum yield has been observed (Φ fl ≥ 0.5) in nonpolar solvents. Φ fl also markedly increases as the viscosity of the nonpolar medium increases, as a result of hindrance of the internal…”

“…The photophysical properties of organic compounds with electron-donor and electron-acceptor substituents have been widely studied recently [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. They are of interest in connection with their possible application as organic light-emitting diodes in color graphical displays [6], fluorescent labels and visualizing agents in biological systems [7,8], and also owing to their nonlinear optical properties [9, 10] (high quadratic polarizability β).…”

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

“…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 ).…”