Increase in photoreactivity by chromophore guest inclusion in nanoporous-crystalline polymer films

This study focuses on photodimerization, by UV irradiation at 356 nm of 7-methoxy coumarin (7-MCM) in amorphous and nanoporous-crystalline (NC) films of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO). Kinetics of dimerization are faster for molecules being guests of NC PPO films than for molecules simply dispersed in PPO amorphous films. These differences become very large for high concentrations of the photoreactant, with dimerization degrees close to 20% and 95% for amorphous and NC PPO films, with 7-MCM concentration of 5.0 wt% and 7.7 wt%, respectively. Nearly complete and fast photodimerizations of 7-MCM, even for its high concentrations in NC PPO films, can be rationalized by the inhibition of chromophore self-aggregation in the crystalline channels and inhibition of related quenching mechanisms. Kinetics of photodimerization of the coumarin guest in NC PPO films are comparable with those observed for crystalline coumarin powder and much more efficient than those observed in solutions or in other inclusion compounds.