Chromogenic systems based on 8-(1,3-benzoxazol-2-yl) substituted spirobenzopyrans undergoing ion modulated photochromic rearrangements

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

“…The formed SPP 1 –Zn complex shows a 1:1 stoichiometry and is characterized by a long-wavelength absorption band with a maximum at 525 nm (ε = 32 330 M –1 cm –1 ). The stability constant determination for the zinc complex of SPP 1 has been carried out by means of UV–vis spectroscopy according to the previously described procedure . The UV–vis spectra for SPP 1 –Zn complex for different Zn concentrations are shown in Figure .…”

“…Since the Zn complexes of 1 and 2 are characterized by a broad long-wave absorption band, the determination of the wavelength dependence of the quantum yield has been also carried out. The process of the photoinduced decomposition of the complex can be described by eq where I 0 is the incident light flux (mol L –1 s –1 ), ε′ is the molar extinction coefficient of complex at the irradiation wavelength (L mol –1 cm –1 ), l is the optical path length for the incident light (cm), A ′ = ε′[Zn–MC] is the optical density of the solution at irradiation wavelength, and C 0 is the complex concentration at t = 0. The current value of the complex concentration [Zn–MC] can be obtained from the solution absorption spectra recorded under irradiation using Beer’s law [MB] = A λ /ε λ l .…”

“…As it has been recently shown, 8-benzoxazole-substituted spiropyrans interact in the dark with transition-metal ions, particularly with zinc cations, producing intensely colored complexes. 40 Indeed, SPP1, as well as its benzoxazole analogue 2, interacts with zinc ions: upon addition of zinc perchlorate to a colorless SPP1 or 2 solution in acetone, the appearance of the intense red coloration has been observed. Color changes can be explained by the formation of the Zn−MC complex, as shown in Scheme 1.…”

“…The stability constant determination for the zinc complex of SPP1 has been carried out by means of UV−vis spectroscopy according to the previously described procedure. 40 The UV−vis spectra for SPP1−Zn complex for different Zn concentrations are shown in Figure 1.…”

“…Stability constants were obtained from the fit of the absorption dependence on Zn 2+ concentration shown in Figure 1b. Dependence of the absorbance on the metal-ion concentration was simulated in a model of 1:1 complex formation stoichiometry according to the procedure described in ref 40. Quantitative spectral characteristics of the complexes are listed in Table 1.…”