Thermal, Photochromic and Dynamic Properties of Water-Soluble Spiropyrans

Abstract

Numerous studies in biological and material sciences have used nitro-BIPS, dinitro-BIPS as well as Py-BIPS as versatile photoswitches. Still, the photochemical picture of this class of compounds is far from complete. We present photometric steady-state and ultrafast time-resolved pump/probe spectroscopic measurements on water-soluble derivatives of these three spriopyrans. Our experiments reveal significant differences between the nitro-substituted spiropyrans and Py-BIPS. In contrast to the high resistance of Py-BIPS towards hydrolysis over weeks, the two nitro-BIPS derivatives decompose over hours. The fluorescence properties of Py-BIPS are unique in showing an emission of the spiro photoisomer. The ringopening and -closing reaction of Py-BIPS is accomplished within picoseconds, whereas nitro-derivatives photoisomerize on longer time scales. These long-lived transients indicate either the contribution of triplet states or the involvement of multiple merocyanine isomers in the reaction pathway. Scheme 1. Reversible photochromic reaction between the closed spiropyran (SP) and the open-ring merocyanine (MC, TTC comformation) isomer of the BIPS compound (top and middle). The three water-soluble spiropyran derivatives (1-3) investigated in this study (bottom)..

The evolution of spiropyran: fundamentals and progress of an extraordinarily versatile photochrome

“…87 The proposed intermediacy of the protonated cisoid form was supported by Shiozaki shortly thereafter, 88 who showed a better-defined response to protonation of spiropyran in ethanol with sulfuric acid than with the more commonly used trifluoroacetic 68,69,[89][90][91][92][93][94][95][96][97] and hydrochloric acids. 18,[98][99][100][101][102][103][104][105][106][107][108][109] These observations indicate that distinct protonated cisoid and transoid structures differ in pK a . Indeed, the dependence of the acidochromic response on the acid employed enables access to pH-gated photochromism in both indolinobenzospiropyran as well as 6-nitroindolinobenzospiropyran when the acids are stronger than the phenolates formed upon ring opening (Scheme 15 and Fig.…”

“…122 Notably, incorporating a pyridinium in the chromene moiety of similar water-soluble spiropyrans greatly increases aqueous thermal stability to weeks by favouring the more stable ring-closed spiropyran form, while still operating as a photoacid. 109,123,124 The application of spiropyrans, typically but not only the sulfonate form, as a photoacid requires that the apparent pK a of the acid to be deprotonated is greater than that of the ringclosed spiropyran, but less than that of the ring-opened E-form (Scheme 16). Thus, UV-irradiation provides access to the protonscavenging E-form, while subsequent visible light induced E to Z isomerization (i.e., 455 nm, see Scheme 15) leads to deprotonation of the Z-merocyanine with concomitant spontaneous ring-closing.…”

Theoretical study on the reaction mechanism of the thermal cis–trans isomerization of fluorine-substituted azobenzene derivatives

“…[1][2][3][4][5] Because of their unique photochromic characteristics, 6 they have been widely used in molecular data storage, 7-9 photopharmacology, 10 optochemical genetics, 11 materials science, 12 and biomolecules 13,14 among other areas. Over the past few decades, most research has been focused on azobenzenes, 15 spiropyrans, 16 diarylethenes, 17 and stilbenes 18 which are all characterized by photoisomerization. Among these molecules, azobenzene, which is based on the diatomic structure N]N, has unique structural characteristics and can be used for optical control under different conditions.…”

Isomerization and Properties of Isomers of Carbocyanine Dyes

“…Photoisomerization (followed by back isomerization of a photoisomer) is one of the main properties of polymethine dyes; at present, it is being studied in detail with the use of modern micro-, nano-, pico-and femtosecond techniques. While trans-cis (photo)isomerization of various compounds is widely used in molecular photoswitches, over the past decades, most works have been focused mainly on azobenzene derivatives [63], spiropyrans [64], diarylethenes [65], and stilbenes [66], and, until recently, this property of cyanine dyes has not been applied in practice. The use of cyanine photoisomerization in research is mainly for probing microviscosity of microheterogeneous media [67,68].…”