Operando XAS and UV–Vis Characterization of the Photodynamic Spiropyran–Zinc Complexes

Abstract

Thermal and photoinduced processes accompanying complexation of photochromic spiropyrans (SPP) with Zn ions in acetone solution were characterized by means of UV−vis and X-ray absorption spectroscopies in operando regime. SPP ligands are usually transparent at λ > 350 nm, but after mixing with Zn ions, they produce a stable colored (ε = 32 000−38 000 M −1 cm −1 ) complex with maximum absorption at 525 nm, which makes them a powerful tool for monitoring metal-ion concentration in solution. The complex revealed fluorescence and photochromic behavior under static irradiation with visible light with constant photoreaction quantum yield across its characteristic absorption band. Zn K-edge X-ray absorption spectra show prominent changes in Zn local atomic structure between free Zn ions and Zn complex. The pump−flow−probe scheme was adapted to measure operando changes in Zn coordination upon light irradiation. Within experimental time resolution, we have determined that 20 μs after light irradiation, Zn ion is released out of the complex. This is the first example of the direct spectroscopic probe of the Zn photorelease from the spiropyran complex.

A Future Perspective on Phototriggered Isomerizations of Transition Metal Sulfoxides and Related Complexes

“…While TR-XAS has been employed with great success to elucidate photophysical mechanisms in transition metal complexes, , we know of few such studies involving photochromic compounds. For example, Chernyshev, Guda and co-workers reported Zn 2+ release from a Zn 2+ -coordinated merocyanine (MC) dye complex from Zn K-edge X-ray absorption near-edge structure (XANES) spectroscopy . Irradiation of the Zn 2+ -MC dye prompts release of Zn 2+ and subsequent photocyclization to produce the ground-state spiropyran.…”

“…For example, Chernyshev, Guda and co-workers reported Zn 2+ release from a Zn 2+ -coordinated merocyanine (MC) dye complex from Zn K-edge X-ray absorption near-edge structure (XANES) spectroscopy. 58 Irradiation of the Zn 2+ -MC dye prompts release of Zn 2+ and subsequent photocyclization to produce the ground-state spiropyran. The reaction was also monitored by UV−visible spectroscopy, as Zn 2+ coordination greatly enhances the extinction coefficient of the ring-opened (MC) isomer.…”

Modelling the effects of E/Z photoisomerization of a cyclocurcumin analogue on the properties of cellular lipid membranes

“…Furthermore, by modifying the structure of photosensitizers, it is possible to change their absorption properties and tune the illumination wavelength required to activate them. Globally, photoswitches comprise several classes of molecules as azobenzenes, 32 spiropyrans, 33,34 diarylethenes, 33 in which light is used to convert the double carbon bond from E-to Z-conformation or to perform photocyclization reactions where the closed-ring specie converts to the open-ring isomer causing changes in the mechanical properties of its environment. The use of non-toxic, natural available, or bio-analogues switches is also particularly attractive to limit general toxicity and side-effects.…”