Bisarylindenols: fixation of conformation leads to exceptional properties of photochromism based on 6π-electrocyclization

Abstract

Thermally irreversible photochromic 1-tert-butyl-substituted 2,3-bisthiazolylindenol has been synthesized. It showed perfect diastereoselectivity and high ring-closing quantum yield with high conversion ratio to the closed form. The collaborative interaction of two intramolecular hydrogen bonds and the steric restriction fixed the conformation in favour of cyclization in a highly diastereoselective manner.

Efficient Self‐Contained Photoacid Generator System Based on Photochromic Terarylenes

“…Interestingly, all PAGs showed solvent‐dependent QY for the acid generation, decreasing the φ acid with increasing the solvent polarity. The parent molecule bisarylbenzo[ b ]thiophene with methyl groups at both ends of 6π‐system showed a photon‐quantitative ring‐cyclization reaction, which indicates the efficiency of the electrocyclization reaction is predominantly dependent on the geometry around the photoreactive 6π‐system in the ground state . Since the acid ester groups introduced at a reactive carbon atom have negligible electronic effect on the photoreactive 6π‐system, the conformational fluctuation must depend on solvent effects and thus may explain the diversity of φ acid values.…”

“…Although this value is rather larger than most of practical PAGs, there should be room for substantial improvement considering the capability of the mother compound, which showed a photon‐quantitative reactivity (QY=0.98) . As much effort have been devoted to the improvement of ring‐cyclization sensitivity of diarylethene and its analogues, we were highly motivated to explore further photosensitive PAGs by developing molecular scaffolds inspired by previous developments in the field, which aim to maximizing the population of the photoreactive conformation in the ground state . Although the bisthiazolylbenzo[ b ]thiophene molecule showed much suppressed photoreaction quantum yield in methanol, the replacement of one of the thiazolyl moieties with a thiophene derivative, which formed an asymmetric terarylene, interestingly led to a large improvement of the QY in methanol .…”

Introduction: Organic Photochromic Molecules

“…This feature was exploited further to undergo stereospecific reactions, where each enantiomer of the open form leads to a specific closed-form enantiomer [121] (Figure 1.40). Another example with a chiral center leads to a 100% diastereoselective process with a A→B value of 85% (Figure 1.41) [122]. …”

“…Figure 1.41 Stereospecific photochromism resulting from the control of the conformation of the open form by intramolecular hydrogen bonds[122].…”

Facile synthesis of photoactive diaryl(hetaryl)cyclopentenes by ionic hydrogenation

“…In the last decades photochromic diarylethenes bearing azole units [28][29][30][31][32] have attracted much attention because of their potential ability to form hydrogen bond and the possibility of its application as an effective tool for the spatiotemporal control of switchable biological systems. 33 Therefore, the development of an alternative method for the preparation of diary(hetaryl)lcyclopentenes based on azoles, primarily unsymmetrical, is of most importance for the design of new smart materials for various fields of science, medicine and technology.…”