Ring opening/closure reactions of novel diheteroarylethenes derivatives. Solvent effects

Abstract

Three novel diarylethenes derived from benzothiophene were synthesized and their photochemical optical properties studied in four solvents (n‐hexane, toluene, acetonitrile and methanol). It was determined that these compounds dramatically increase the light absorption in the visible region upon exposure to UV light, showing two absorption maxima at 420 nm and 520 nm, respectively. The observed change is completely reverted upon exposure to visible light. The three compounds demonstrate negligible fatigue, excellent stability in the four solvents, and absence of photodegradation and thermal back reactions. This paper also describes a complete study of solvent effects on the kinetics of the ring opening and cycloreversion. While, the UV spectra are little sensitive both to the substitution pattern and to the solvent influence, the kinetics of ring opening/cycloreversion reactions exhibit a more interesting behavior that differs from other diarylethenes reported in the literature. The cyclization kinetics shows a complex order, well fitted by an exponential equation, while the cycloreversion presents first‐order kinetics. The whole complex reaction scheme can be explained by the unusual presence of two conformers of the open form, a parallel and an antiparallel conformation. Though other alternative mechanism could explain the kinetics, additional evidence is consistent with the conformational equilibrium proposed: i.e. the solvent influence on the kinetics of the nitro‐substituted substrate, and the double signals for the methyl protons and for the methoxy protons (when present) observed in the nuclear magnetic resonance spectra. These observations are relevant in relation to the application of these novel diarylethenes as potential optical materials. Copyright © 2012 John Wiley & Sons, Ltd.

Helically Chiral 1-Sulfur-Functionalized [6]Helicene: Synthesis, Optical Resolution, and Functionalization

“…Thus, the utilization of ( P , S , S )- 8b as a chiral building block afforded enantiopure [7]­thiahelicene ( P )- 4 as shown in Scheme . Removal of the chiral auxiliary of ( P , S , S )- 8b by NaOMe, subsequent alkylation with 1,1-diethoxy-2-iodoethane, and formation of the thiophene ring mediated by boron trifluoride diethyl etherate (BF 3 ·Et 2 O) gave enantiopure [7]­thiahelicene ( P )- 4 in 66% isolated yield over three steps. Enantiomer ( M )- 4 was prepared similarly from ( M , S , S )- 9b ; the structures of ( P )- 4 and ( M )- 4 were identified by NMR and HRMS.…”

New insights into the photocyclization reaction of a popular diarylethene switch: a nonadiabatic molecular dynamics study

“…For most DAE molecules, two ground-state conformers of the OF exist in equilibrium: a parallel (P) rotamer, with the two side-rings being mirror reflections of each other (C s symmetry), and an anti-parallel (AP) rotamer, exhibiting C 2 symmetry. [18][19][20] Because of the Woodward-Hoffman rules, 21,22 only the AP rotamer is reactive in the photoswitching process. Both the cyclization and cycloreversion processes are assumed to proceed through a common conical intersection, involving breaking/formation of the central C 1 -C 6 bond between the reactive carbon atoms.…”

Light-Triggered Reversible Tuning of Second-Harmonic Generation in a Photoactive Plasmonic Molecular Nanocavity

“…In the simulation, we set n = 1.63 for the host−guest complex with both open and closed forms of DAE molecules according to the reported value. 54 For the molecular complex with an open form of DAE molecules we set k = 0 because the absorption spectra of the molecular solution under original state and after visible light illumination are quite low within the measured wavelength range (Figure 1a). For the molecular nanocavity with an open form of DAE molecules, we find that the predominant resonance wavelength of the scattering spectrum matches well with the statistical result (around 722 nm) under the experimental measurement when d = 2 nm (determined by the molecular length of DAE), as shown by the olive line in Figure 3c.…”

“…The molecular layer is modeled as a dielectric layer with thickness d and a complex refractive index n + ik . In the simulation, we set n = 1.63 for the host–guest complex with both open and closed forms of DAE molecules according to the reported value . For the molecular complex with an open form of DAE molecules we set k = 0 because the absorption spectra of the molecular solution under original state and after visible light illumination are quite low within the measured wavelength range (Figure a).…”