Photon‐Quantitative Reaction of a Dithiazolylarylene in Solution

Abstract

In the cascade of mammalian vision, the cis-to-trans photoisomerization reaction of the retinal chromophore bound to the opsin apoprotein acts as the first trigger for the conversion of light signals into electrical pulses, which are finally transmitted to the brain. One of the specific chemical characteristics of retinal chromophore is its high quantum yield of cis-to-trans photoisomerization, F cis-trans = 65 %, which affords the high sensitivity of the rod rhodopsin, an opsin-retinal complex required for night vision.[1] Interestingly, the F cis-trans value of retinal decreased to less than 30 % in solution without the protein. This observation suggests that the environmental conditions of the binding pocket in rhodopsin may be responsible for the high photochemical reactivity of retinal. The hydrophobic pocket in rhodopsin is thought to favor appropriate noncovalent bonding to regulate the geometry of the guest molecule in preparation for the photoisomerization reaction.[2] With the aim of developing highly efficient and sensitive photochromic molecules on the basis of the opsin-retinal system, we designed an organic photochromic molecule with a terarylene structure and demonstrated its photon-quantitative reaction.Photochromic terarylenes are composed of three aromatic rings connected to form a hexatriene backbone, [3] which is converted into a cyclohexadiene structure upon UV irradiation, as similarly observed for the photochromism of diarylethenes.[4] Recent studies on terarylenes have highlighted their high photocyclization quantum yields, which exceed 60 % [3b,d, 5] and are apparently higher than those of conventional diarylethenes.[4] Since the photoelectrocyclic reactions typically occur in less than 200 fs, the photocyclization quantum yield is generally determined by the electronic structure in the excited state, which is directly interpreted as the molecular conformation in the ground state. Diarylethenes are known to possess two conformations in solution, with the two rings in mirror symmetry (parallel conformation) or C 2 symmetry (antiparallel conformation). As the photocyclization reaction proceeds only from the C 2 -symmetrical conformation, the quantum yield is about 50 % at most.[4a] In contrast, some diarylethenes undergo a quantitative photocyclization reaction in the crystalline state, when their conformation is fixed in the antiparallel conformation and the distance between reactive carbon atoms is sufficiently short: typically less than 0.4 nm.[6] These observations indicate that the ground-state conformation plays a crucial role in the photoinduced pericyclization reaction. Therefore, various attempts have been made to regulate the ground-state geometry of diarylethenes so that they have C 2 symmetry. [7] We herein propose a concept for the design of highly reactive photochromic hexatriene molecules that is inspired by the design of foldamers; [8] thus, multiple intramolecular interactions were used to stabilize the photoreactive conformation of a terarylene.The 2,3-dithiazolylbenz...

Intramolecular Hydrogen Bonding in a Triangular Dithiazolyl‐Azaindole for Efficient Photoreactivity in Polar and Nonpolar Solvents

“…[19] Because both molecules are composed of similar molecular units and display dual non-covalent intramolecular interactions, one may expect similar photochromic reactivity. Indeed, the photochromic quantum yield of 1a was similar to that of 3a in hexane (90 % for 1a and 98 % for 3a), whereas that of 3a was significantly suppressed in methanol.…”

“…The authors recently reported that a dithiazolylbenzothiophene derivative shows a photon-quantitative reaction with almost 100 % photocyclization quantum yield. [19] This extremely high photochromic reactivity of the molecule was explained in terms of specific intramolecular S/N and CH/N non-covalent interactions, which were thought to stabilize the C 2 -symmetric conformation in nonpolar solvents. In the field of supramolecular chemistry, intramolecular and inter-arylene unit interactions have been developed to regulate the rotational configuration of oligoarylene molecules forming specific foldamers.…”

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.…”

Substitution effect on the photochromic properties of benzo[b]thiophene-1,1-dioxide based diarylethenes

“…The rates of isomerization in the initial stage of the reaction (0-5%) were compared with reference whose Φ oc (35%) in hexane are known, which brought forth 5% Please do not adjust margins Please do not adjust margins uncertainties on the calculations of quantum yields. 43 Absorption changes were monitored by a CCD camera mounted on a Princeton spectrometer instrument.…”