A Picosecond Time-Resolved Spectroscopic Investigation of the Effect of pH on Morin Fluorescence.

In this work, we investigated for the first time morin in MeOH at different pH values by picosecond time-resolved fluorescence. We identified the two species responsible for the fluorescence at low and high pH. The solvated morin-solvent hydrogen-bonded complex has been experimentally observed for the first time. We give also the typical fluorescence spectra as well as the fluorescence lifetimes of the probable emitting species. In this work we put forward new insights concerning the contribution of free morin to the fluorescence. We hope that these new data improve the accuracy of the interpretation of the cation:morin complexes titration using fluorescence signal.

Determination of Electronic Recombination Free Energy in Zeolites: Effects of the Charge Balancing Cation and Confinement.

The adsorption of DPH in M6.6 ZSM-5 (M=Na+ , K+ , Rb+ , Cs+ ), RbFER and RbMOR channel zeolites takes place without chemical or structural modification. After photoexcitation of these systems, a radical cation-electron pair is observed and has a sufficiently long lifetime to be studied by diffuse reflectance UV-visible spectroscopy. The study of the recombination of this radical cation-electron pair was carried out at different temperatures and allowed the determination of the activation energy as a function of the nature of the charge-balancing cation but also of the confinement effect. It appears that the activation energy decreases progressively from Na+ to Cs+ but also when the confinement decreases. To go further, the free enthalpies have been calculated from the Marcus theory demonstrating experimentally that these systems are located in the inverted Marcus region.

Photoinduced electron transfers in zeolites: impact of the aluminum content on the activation energies.

We report the activation energy determination corresponding to the recombination of the radical cation electron moiety created through photoionization of the 1,6-diphenyl-1,3,5-hexatriene molecule incorporated in ZSM-5 zeolite channels. We demonstrate that the charge separated state stabilization in zeolite does not depend only on the Al content but also on the Al repartition.