Spatial confinement alters the ultrafast photoisomerization dynamics of azobenzenes

Abstract

Ultrafast transient absorption spectroscopy reveals new excited-state dynamics following excitation of trans-azobenzene (t-Az) and several alkyl-substituted t-Az derivatives encapsulated in a water-soluble supramolecular host–guest complex.

Dynamics of Anthracene Excimer Formation within a Water-Soluble Nanocavity at Room Temperature

“…The calculated potential energy curves are consistent with the experimental observations. The results presented here support the conclusion that molecules on confinement behave differently. − In addition, the dynamics displayed by two anthracene molecules in a confined space discussed here provides insight into photodimerization reactions of organic molecules in restricted spaces offered by crystals, templated structures, biological systems, and host–guest complexes…”

Photochemical control of bacterial gene expression based on trans encoded genetic switches

“…These results can be explained by the spatial confinement effect which plays a pivotal role in photoisomerization of azobenzenes. 35 Our photo-switchable compounds are composed of two bulky paromomycin molecules linked by an azobenzene group and the compounds require a high degree of conformational freedom to switch between the two photo-isomeric forms. However, when the E isomer binds to the aptamer domain of the switch, the compound encounters a sterically hindered environment that confines space and hinders free rotation to convert the E to Z isomer.…”

Altered relaxation dynamics of excited state reactions by confinement in reverse micelles probed by ultrafast fluorescence up-conversion

“…159 The classical cis-trans isomerization of azobenzene incorporated into the hydrophobic cavity of another supramolecular complex was observed. 160 The rate of the excited state reaction was again slowed down, and the photochemical yields modified by the confinement.…”

“…Very recently there have been some time resolved transient absorption studies in strongly confining media by Otolski et al 160,167,168 For a series of encapsulated azobenzene and stilbene derivatives they observed both significant lengthening of excited state lifetimes and the opening up of new isomerization pathways. It was suggested that spatial confinement modifies the topology of the conical intersection with the ground electronic states, thus excited state lifetime and the photoproduct yield.…”

“…These effects were found to be quite dependent on the precise molecular structure of the stilbene derivative. 160 Variation of the confining medium in such systems will provide important information on its coupling to the reaction coordinate.…”