Energy deactivation pathways of porphyrins and dopa melanin in polyvinyl alcohol systems.

Absorption, fluorescence, delayed luminescence and photoacoustic spectra ha ve been measured to learn about the radiative and non-radiative processes i n two porphyrins: (4-N,N,N,N-trimethylanilinium) porphyrin (TAP) and (4-sul phonatophenyl) porphyrin (TPPS4) and their mixtures with a synthetic dihydr oxyphenylalanine (dopa) melanin in polyvinyl alcohol (PVA) solution and in PVA film. Due to ionic interactions, the positively charged TAP in its grou nd state forms a complex with dopa melanin. Absorption and emission spectra show that the TAP-dopa melanin complex is preserved in PVA solution, where as when the complex is embedded in PVA film a competitive interaction betwe en the PVA and dopa melanin in the dye-polymer complex is observed. In the case of TPPS4, no strong interaction between dye and polymer has been obser ved either in PVA solution or in PVA film. Our photoacoustic spectra indica te that dopa melanin in both PVA solution and in buffer solution liberates heat promptly. Evidently, the PVA matrix does not affect, to any significan t extent, the thermal properties of dopa melanin. The casting of PVA film c hanges the interaction of dopa melanin with porphyrins and in consequence t heir thermal properties. Under such conditions, porphyrin and dopa melanin behave like individual species. The new results are compared with spectrosc opic data previously obtained for TAP and TPPS4 in phosphate buffer solutio n, and show that phosphate buffer solution and PVA solution are suitable me dia for porphyrin-dopa melanin complex electron exchange study, whereas the PVA film can be an appropriate system for investigation of the energy tran sfer process between porphyrin and dopa melanin. (C) 1998 Elsevier Science S.A. All rights reserved.