Photophysics and photochemistry of porphyrin core PAMAM dendrimers. Excited states interaction with quinones

MILITELLO, M. PAULA; ARBELOA, ERNESTO M.; HERNÁNDEZ RAMÍREZ, RAQUEL E.; LIJANOVA, IRINA V.; MONTEJANO, HERNÁN A.; PREVITALI, CARLOS M.; BERTOLOTTI, SONIA G.

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

ELSEVIER SCIENCE SA

Año: 2020 vol. 388

1010-6030

Quenching of excited states of the meso-substituted tetraphenyl porphyrins with PAMAM branches, and one withPAMAM generation 1 peripherally-modified with thiazole groups by p-benzoquinones, were studied in DMFsolution. Fluorescence lifetime measurements evidence a static component in the quenching process. The dynamicquenching rate constants were close to the diffusional limit except for the case of duroquinone. Apparentassociation constants of the porphyrin compounds with the quinones were determined by comparison of staticand dynamic measurements of fluorescence quenching. The ground state interaction is very weak with theexception of tetrachlorobenzoquinone. The triplet state decay kinetics and the transient absorption spectra in thepresence of the quinones were determined by laser flash photolysis. Triplet quenching rate constants were lowerthan those of singlet quenching. An electron transfer mechanism was proposed to explain the results. The longtimetransient absorption spectra were assigned to the radical cation of the dyes. Relative radical yields weredetermined and a dependence on the side chains and the quencher was observed.