No abstract

Addition of a bis(trichloromethyl)‐substituted‐1,3,5‐triazine (Tz) to a dye/amine photoinitiating system leads clearly to an increased efficiency of polymerization under visible light irradiation. The polymerization rates obtained with three triazine derivatives with either phenosafranine, eosin or Rose Bengal as light absorbing species, were measured. Whatever the investigated dye/amine mixture, the addition of Tz led to a strong synergistic effect: the inhibition time decreased and the polymerization rate increased significantly when the three components were used jointly. The spectroscopic and redox properties of the Tz were measured. The system dye/amine/Tz was investigated through time‐resolved laser spectroscopy and steady state fluorescence experiments. A detailed reaction mechanism was elaborated which shows that Tz acts mainly as an inhibitor scavenger. The involved inhibitor is the reduced dye (DH∗︁) arising from the first photochemical reaction between the excited states of the dye and the amine.

The free ion yield (OR) resulting from the fluorescence quenching of 9,lO-dicyanoanthracene (DCA) by various electron donors in acetonitrile has been studied using ns laser photoconductivity. The influence of the chemical nature of the doors is established in a general manner. For a given oxidation potential €,,(DID+), the rate constant of geminate ion recombination, kbac , decreases significantly as the electronic delocalization of the donor increases. As a consequence multiple Marcus plots are observed in the inverted region. These plots show decreasing curvature when going from stilbenes to amines as donors. This 'fan effect' is tentatively explained by considering the detailed roles of the parameters V , I and h v in the Marcus model.

No abstract

No abstract

No abstract

Abstract— Fluorescence quantum yields and singlet lifetimes for a wide range of hydrophilic to hydrophobic porphyrins and metalloporphyrins have been determined in toluene, methanol or acetone. Photosensitized singlet oxygen yields have been determined in the same solvents. For some porphyrins, the same quantities were determined in an aqueous medium, through use of an amphiphilic polymer to solubilize the porphyrin sensitizer and target molecule, 1, 3‐diphenylisobenzofuran. Because rate constants for the deactivation of singlet oxygen (kd) and for its reaction with a target molecule (ka) are unknown in such aqueous polymer systems, a new method was developed for evaluating yields of singlet oxygen formation that also provides a value for the ratio kd/ka. A variation observed in quantum yield of singlet oxygen production for the aqueous polymer system with variation in initial concentration of the target molecule is discussed.

No abstract