Kinetics of photochromic reactions in condensed phases

Thermal cis-to-trans isomerisation of triazene dyes in doped polymer films

“…Kinetic traces corresponding to thermal cis-to-trans isomerisation of DPT in doped PMMA or PS films in the glassy state cannot be fitted with a single exponential function, a common observation with photochromic unimolecular reactions taking place in constrained reaction media like polymer matrices [11]. Deviations from first-order kinetics are typically attributed to the inhomogeneous distribution of local free volume (sites) in the polymer matrix, hence imposing a distribution of localized barriers on the steric requirements of the reaction, as often reported for thermal cis-totrans isomerisation of azobenzenes in polymer films [12], for example.…”

Synthesis and characterization of two new photochromic inorganic-organic hybrid materials based on Keggin-type polyoxometalates

“…Although reports concerning photochromism of solid POM-based inorganic-organic hybrid materials have evidently increased in recent years [3][4][5][9][10][11][12][13][14] , the information on their photochromic behaviour is scarce, usually incomplete and in most cases lacking kinetic data [15] . Keggin-and Dawson-type polyoxometalates are extensively used as the building blocks for the construction of inorganic-organic hybrid materials because of their special structures, high electronic density and redox properties.…”

Optical gating with organic building blocks. A quantitative model for the fluorescence modulation of photochromic perylene bisimide dithienylcyclopentene triads

“…In order to quantify the evolution of the photoreaction of photochromic molecules a lot of efforts have been taken during the last two decades. Most of this work was based on experiments that monitored the absorption signals678212223242526272829. However, a simple relation between the macroscopic absorbance of the sample and the concentration of the photochromes, as for example provided by Lambert Beer's law, does not hold, because the concentration of the absorbing species varies in time (and space) due to the photoreaction, which in turn leads to uncontrollable variations of the light intensity that is “seen” by the photochromic molecules.…”

“…However, a simple relation between the macroscopic absorbance of the sample and the concentration of the photochromes, as for example provided by Lambert Beer's law, does not hold, because the concentration of the absorbing species varies in time (and space) due to the photoreaction, which in turn leads to uncontrollable variations of the light intensity that is “seen” by the photochromic molecules. This can be overcome by working with absorption cells where the solution is continuously stirred29, but remains an obstacle for immobilised samples and complicates to find an analytical description of the kinetics of the photoconversion as a function of the irradiation intensities222330. On first sight, using the emitted fluorescence for monitoring the photoconversion seems to be even worse, because the number of photons emitted from a fluorophore depends on the number of photons that have been initially absorbed.…”