Radiative Dynamics in Solution and in Molecular Assemblies of an H-Aggregate-Forming Stilbazolium Amphiphile

Abstract

Radiative dynamics of the hemicyanine dye N- (3-sulfopropyl-4-(p-dioctylaminostyryl)pyridinium (I) have been studied in primary alcohols and in Langmuir-Blodgett (LB) monolayer films by using time-resolved laser-induced fluorescence spectroscopy. In solution, the deactivation of the optically excited state is dominated by a radiationless transition via an activated barrier crossing to the twisted intramolecular charge transfer (TICT) state, and the decay rate decreases substantially with increasing n in the series CH 3 (CH 2 ) n OH. Observed biexponential decays are consistent with the three-level scheme describing the horizontal transition on the excited-state potential surface. In monolayer films the decay dynamics are similar whether the initial excitation occurs into the monomer or aggregate bands. The kinetics are interpreted in terms of diffusion of excitons in the aggregate with eventual energy transfer to the monomer. A Monte Carlo simulation was used to characterize the motion of the excitons within aggregates and to correlate the aggregate size with exciton lifetime. The finite size of the aggregate in monolayer films was estimated under two limiting cases: one in which exciton transport on the aggregate is the rate-limiting step in emission and another in which aggregatemonomer excitation transfer limits the radiative rate. Comparison of experimental and simulated results yielded an estimate of the size of an H-aggregate in monolayers of I to be ca. 45 molecules in the first case and 50 molecules in the second. A comprehensive kinetic scheme is presented that unifies both the solution and monolayer film behavior observed in these studies.

On the Adsorption Behavior of Soluble, Surface-Chemically Pure Hemicyanine Dyes at the Air/Water Interface

“…There is no indication of the presence of cis isomers, either as a by-product of the synthesis or by photochemical trans-cis isomerization. This is in contrast to the behavior of the analogous merocyanines (20,21), but in agreement with the unfavorable trans-cis equilibrium of analogous long-chain-substituted hemicyanines in water, even in the photostationary state (22).…”

“…Further, NMR spectroscopy and TLC did not show any decomposition of the chromophores in aqueous solutions after 3 weeks of storage at room temperature in day light [e.g., due to hydrolysis by retro-aldol reaction (23) or due to photoreactions (22,24)], thus indicating sufficient stability of the compounds for the duration of the experiments performed.…”

Photophysical Studies on the Mono- and Dichromophoric Hemicyanine Dyes II. Solvent Effects and Dynamic Fluorescence Spectra Study in Chloroform and in LB Films

“…Their photophysical properties, that is, absorption, fluorescence, nonlinear optical phenomena (second harmonic generation (SHG), two-photon absorption, laser application), and photoelectric conversion (PEC) have been widely reported. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] As one of the most efficient SHG chromophores, it has many derivatives that have been designed and synthesized to improve its SHG property. 15,16 Stilbazolium is also a useful chromophore as a voltage-sensitive membrane probe, especially used in cell biology.…”

Photophysical Studies on the Mono- and Dichromophoric Hemicyanine Dyes III. Ultrafast Fluorescence Up-conversion in Methanol: Twisting Intramolecular Charge Transfer and “Two-State Three-Mode” Model

“…Their photophysical properties, that is, absorption, fluorescence, nonlinear optical phenomena (second harmonic generation (SHG), two-photon absorption, laser application), and photoelectric conversion (PEC) have been widely reported. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] As one of the most efficient SHG chromophores, it has many derivatives that have been designed and synthesized to improve its SHG property. 15,16 Stilbazolium is also a useful chromophore as a voltage-sensitive membrane probe, especially used in cell biology.…”