Photo- and thermochromic spiranes. 31.* Photochromic cationic spiropyrans with a pyridinium fragment in the aliphatic side chain*2

Abstract

Syntheses are reported for cationic indoline spiropyrans with a quaternized pyridinium fragment in the aliphatic side chain, which display photochromic properties in solution. The major effect of introducing a quaternized pyridinium fragment into the benzopyran part of the spiropyran entails a significant decrease in the rate of thermal relaxation processes.Keywords: cationic indolinospiropyrans, pyridinium fragment, photochromism, electronic absorption spectroscopy.Photochromic organic molecules, some of which are spiropyrans and spirooxazines, have recently been the subject of intensive research due to the use of these compounds in optical recording and data transformation systems, sensors, optical electronics, optical bioelectronics, and transport systems [2-5].However, the limit to improving the characteristics of monofunctional materials has now been reached and attention is being directed toward the development of hybrid polyfunctional materials holding promise for application in molecular electronics.A possible solution of this problem lies in the creation of hybrid polyfunctional materials, which combine structural units responsible for different physicochemical properties such as photochromism and magnetism [6][7][8][9], photochromism and conductivity [10,11], electrical and magnetic properties [12], and optical dichroism and magnetism [13]. A systematic study of both the structure and properties of such units and the feasibility of their combination into a single crystal lattice is required for the development of such materials from molecular units differing in their chemical nature, the investigation of the interaction of such units on each other, and methods for the modification of the properties of the separate units to impart desired properties to the hybrid materials. _______ * For Communication 30 see [1]. * 2 Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. __________________________________________________________________________________________

Accidental degeneracy in the spiropyran radical cation: charge transfer between two orthogonal rings inducing ultra-efficient reactivity

“…Likewise, their respective singlet cationic counterparts have been shown to display photochromism in both solution 6,7 and crystalline state. 8,9 These have been employed in a variety of applications.…”

“…10 Other uses are related to biological applications, where a water-soluble photochrome is needed. [11][12][13] Although the thermal reversibility of this transformation has been exploited extensively in applications, thermally stable MC isomers have been attained in solution, as shown by Minkin and coworkers 7 through the addition of cationic substituents, by Kortekaas et al through protonation of the pyran oxygen atoms of bis-spiropyrans, 14 and in the solid state when embedded in a silica gel. 9 Although the photochromism of spiropyrans has been known for over half a century, their electrochromism has received detailed attention only recently.…”

5′-Substituted Indoline Spiropyrans: Synthesis and Applications

“…3 •H 2 O, whose spiropyran cation contains a quaternized pyridine fragment in the side aliphatic chain was produced. The major effect of introducing a quaternized pyridinium fragment into the benzopyran part of the spiropyran entails a significant decrease in the rate of thermal relaxation processes[143,144]; (b). Photochromic 8-(5-(p-tolyl)-1,3,4-oxadiazol-2-yl)-substituted SP175, SP176, which are able to undergo light-controllable cation-induced isomerizations, have been prepared.…”