Kinetic Analysis of Photochromic Systems under Continuous Irradiation. Application to Spiropyrans

Abstract

The kinetics of spiropyran photochromic systems in solution in a stirred batch reactor continuously irradiated with monochromatic light was studied by UV/visible spectrophotometry. The plots of absorbance vs time were analyzed, and the desired parameters (quantum yields, UV/visible spectrum of the unstable photomerocyanine, ...) were extracted from an iterative computation which fitted the calculated curves to the experimental ones on the basis of a representative model of the reaction mechanism. The method was applied to spiro[benzothiazoline-2‘,2-benzopyran] whose corresponding photomerocyanine has a lifetime of 100 s in toluene; the two quantum yields of the direct process of photocoloration and the reverse reaction of photobleaching could be determined along with the spectrum of the corresponding photomerocyanine. To demonstrate the general nature of the photokinetic method, it was applied to the reaction of spiro[indoline-2‘,2-benzopyran], where the main photochromic process is accompanied by a photodegradation. Despite this interfering phenomenon, the photokinetic method could be used to extract the parameters of the main photochromic process. It also showed that the photodegradation products catalyzed the thermal back-isomerization. The order of magnitude of the rate constant of this catalytic process and the quantum yields of photodegradation were estimated.

Molecular switches as photocontrollable “smart” receptors

“…In the latter, visible light at a higher wavelength or continuous UV irradiation can be utilized. 72 The closed and open isomers of a spiropyran are different chemical species that can undergo different reactions. This represents the basis for several applications in chemical sensing.…”

Organic photochromism (IUPAC Technical Report)

“…The only simplifying hypothesis that is used for their establishment is that the well-stirred mixture obeys Beer's law. UV/visible multiwavelength analysis of absorbance vs. time curves recorded under continuous monochromatic irradiation provides information about the evolution of the corresponding concentrations [36]. Simulated curves from numerical integration of the differential equations generated from the kinetic scheme are compared with the experimental curves using curve-fitting procedures.…”

Metal complexes of the merocyanine form of nitrobenzospyran: Structure, optical spectra, stability

“…e MC data are available only for a few other spiropyrans. They were determined by photokinetic measurements carried out at different photon fluxes of the irradiating light [39,41,42], or by measuring simultaneously the NMR and absorption spectra of samples under UV irradiation [40]. The value of the association constants, K 2 , can be estimated if e MC is unknown from the temporal variation of the visible spectra of solutions prepared from the stable SP forms of spiropyrans and metal salts, in the dark and following UV irradiation [43].…”