Fast and Efficient Oxidative Cycloreversion Reaction of a π‐Extended Photochromic Terarylene

Abstract

We report herein a dramatic improvement in the kinetics and efficiency of an oxidative cycloreversion reaction of photochromic dithiazolylthiazoles. The cycloreversion reaction of a colored isomer of dithiazolylthiazole proceeds not only by photo-irradiation, but also through chemical oxidation with a net efficiency far exceeding 100 % owing to a chain reaction mechanism. By introducing aromatic groups on the reactive carbon atoms at the ends of a photoreactive 6π system in a dithiazolylthiazole, the net bleaching reaction rates were increased by up to 1300-fold, and turnover rates increased by two orders of magnitude. Based on a combination of classical kinetic analyses and DFT calculations, we attribute this improvement to acceleration of the rate-determining step to produce the active species in the chain-reaction oxidative cycloreversion.

Photochromic Diarylethenes Designed for Surface Deposition: From Self‐Assembled Monolayers to Single Molecules

“…[80] The charge transfer between surface and molecules is also important in the context of bistable compounds because the properties of the o and c forms in their charged radical states are different from their neutral ones. [28][29][30][31][32][33][34][35][36] Kim's group clearly demonstrated this when they showed that the c form is more stable than the o form in STM studies of 15 (Figure 7a) on metallic surfaces. Deposition and subsequent imaging of the assynthesized o forms resulted in the observation of both o and c forms, seen as extended and triangular lobes respectively, on Cu(111) at room temperature (Figure 7b).…”

“…The charge transfer between surface and molecules is also important in the context of bistable compounds because the properties of the o and c forms in their charged radical states are different from their neutral ones . Kim's group clearly demonstrated this when they showed that the c form is more stable than the o form in STM studies of 15 (Figure a) on metallic surfaces.…”

“…Nevertheless, other strategies for cycloreversion are also available: heating, [25] multiphoton absorption, [26] triplet sensitization, [27] and photo/electrocatalytic chain reactions. [28][29][30][31][32][33][34][35][36] Fourth, Irie and Uchida reported a diarylethene based on a benzothiophene where the aromatic groups have high fatigue resistance. [37] Hecht and co-workers found that electron withdrawing groups also increase fatigue resistance.…”

“…However, the high photocyclization quantum yield comes at a cost of low cycloreversion. Nevertheless, other strategies for cycloreversion are also available: heating, multi‐photon absorption, triplet sensitization, and photo/electrocatalytic chain reactions . Fourth, Irie and Uchida reported a diarylethene based on a benzothiophene where the aromatic groups have high fatigue resistance .…”

Efficient Self‐Contained Photoacid Generator System Based on Photochromic Terarylenes

“…The downfield shifts of these methylp rotons after the photoinduced elimination (Supporting Information, Figures S12, S13) suggested that the ring-current effect of 2-phenylthiazole unit operated on these methyl groups in PAGs 1 and 2.O nt he other hand, bulky substituents on the reactive carbon atoms as aromatic leaving groups markedly decrease the efficiency of electrocyclization reaction for PAGs 3 and 4. [40] In addition for PAG-5,t he S···N interaction operatingb etween the central and the side thiazolyl units, [33] the CH···N interaction between the central thiazole and the side benzo[b]thiophene unit may contribute to the stabilization of photoreactive conformer.B ecause of the hydrogen-bonding nature of CH···N interaction, the f acid value is expectedt os ignificantly drop in protic and polar solvents (0.23 in methanol).…”