Photocyclization reaction of a diarylmaleimide derivative in polar solvents

Abstract

Photochromism of a symmetric diarylmaleimide derivative, having two thiophene rings (1), and a non-symmetric derivative having a S,S-dioxide thiophene ring and a thiophene ring (2) as the aryl moieties, was studied in various solvents. The photocyclization quantum yield of gradually decreased with increasing the solvent polarity and the reaction was not observed in polar solvents, such as ethanol and acetonitrile; on the other hand, such a strong solvent dependence of the photocyclization reaction was not observed for ; the different behavior is attributed to the weaker electron donating ability of the S,S-dioxide thiophene ring.

Highly Efficient Visible‐Light Driven Photochromism: Developments towards a Solid‐State Molecular Switch Operating through a Triplet‐Sensitised Pathway

“…The results of transient absorption studies indicate that the relative yield of photocyclisation in toluene is considerably higher than in acetonitrile. This observation is consistent with previously reported decrease of the photocyclisation yield upon increase of solvent polarity in, for example, 1,2bis(2,4,5-trimethylthiophene-3-yl)maleic anhydride or 1,2bis(2-methylbenzothiophene-3-yl)maleic anhydride, [24] diarylmaleimide derivatives [25] and a variety of similar systems. [7a, 26] The explanation of this effect, proposed previously, was that the energies of the reactive co-planar and non-reA C H T U N G T R E N N U N G active twisted conformations depend on the solvent polarity, with the latter conformation being stabilised in polar solvents, [24] and it is likely that a similar explanation is possible here.…”

A Dithienylethene‐Based Rewritable Hydrogelator

“…New absorbance bands appeared at 360 and 530 nm, with a decrease in absorbance at 290 nm. [29] An isosbestic point was maintained at 326 nm, indicating that side reactions, for example, hydrolysis or degradation, did not occur. The ratio of open/ closed form at the photostationary state was determined to be 92:8 for solutions of the gelator.…”

Nonsymmetrical 3,4‐Dithienylmaleimides by Cross‐Coupling Reactions with Indium Organometallics: Synthesis and Photochemical Studies

“…The open isomers resulted in bright‐yellow solutions in CHCl 3 and their UV spectra showed an intense absorption in the UV range λ =290–340 nm, probably due to the presence of aromatic moieties, and a broad absorption band ( λ =400–420 nm) in the visible range (Table 4). The latter is usually attributed to charge transfer from the electron‐rich thiophene to the electron‐deficient maleimide ring 14e. f The general short range of the absorption band indicates that the substitution at the thiophene has a small effect on the absorption characteristics of the DTEs.…”

“…The reaction rates for these compounds are lower relative to those of other DTEs (i.e., with a perfluorocyclopentene bridge), but similar to those reported previously for other 3,4‐dithienylmaleimides. This behavior can be explained by charge transfer between the thiophene and the maleimide bridges, which can affect the efficiency of the photochemical cyclization and diminish the rate and yield of these reactions and, in some cases, can even afford compounds that do not cyclize under irradiation 14e. f Finally, the rate constants for the second cycle are slightly faster than the first, probably due to a conformational effect if the required antiparallel conformation was favored after the first photocycloreversion.…”