Spectral and kinetic properties of a red–blue pH-sensitive photochromic spirooxazine

Thermodynamic and kinetic analysis of metal ion complexation by photochromic spiropyrans

“…The relevant values of optical extinction are determined by in situ UV Vis spectroscopy using a fiber optic spectrophotometer. 5 Thus,…”

A mathematical analysis and elucidation of AB(2k,1ϕ) thermophotochromic kinetics: Analytical solutions using pure kinetic data and considering as unknown the rate constants, quantum yield, and both species' spectra

“…This conclusion corroborates well with those of previous workers who stated that the total elucidation of the kinetic and spectroscopic parameters without introducing any assumptions is a nontrivial task 2–4. In a recent study, the estimation of the four kinetic and spectroscopic parameter values of the thermophotochromic reaction of a spirooxazine derivative (where the spectrum of the initial species was assumed known at low temperature) required combining UV–vis and NMR data, low‐temperature (243 K) spectral and kinetic measurements, the assumptions that (i) the equilibrium reached under irradiation is shifted toward the open form at low temperature and (ii) the photochemical yield is independent of the irradiation wavelength, and using a simultaneous numerical integration of at least two thermal and four photochemical traces (the later ones were obtained at two isosbestic irradiation and one observation wavelengths) 5.…”

“…Thermochromism is a thermally induced reversible color change that is encountered for a large variety of photochromic organic substances such as spiropyrans, spirooxazines, Schiff's bases, and bianthrones 1,4. The attention received by such materials is largely due to their potential use in a variety of technological applications 1–10. However, the lack of an analytical kinetic elucidation method has made the results obtained so far insufficiently reliable for comparative studies and/or to represent a solid basis for the design and improvement of the properties of new structures.…”

“…From a reaction point of view, a number of these chromic systems can be described by a generic AB(2 k ,1 ϕ) kinetic mechanism 1–14, which consists of opposing thermal steps between the reactive species A and B in addition to a forward photochemical reaction involving the starting material (species A, Scheme ). Of course, the true mechanism will be more complex than that assumed by this generalization, but the other intermediate species (particularly excited states) involved in the overall reaction are characterized by lifetimes several orders of magnitude shorter (<ms) than those of species A and B (in the order of seconds/minutes) 2–4.…”

“…The elucidation approaches proposed, thus far, to solve such kinetics have necessarily involved independent estimation of the effective values of at least one of the unknown parameters, besides considering (or assuming) that the spectrum of the initial species is accessible 1–14. For example, to determine the thermal equilibrium constant ( K e = k AB / k BA ) at a given temperature, the spectrum of B has been estimated by undertaking measurements at low temperature (−75°C) 11, by using iterative methods 12,13, or by the total protonation of the charged species (open form isomers) 14.…”