Different interactions between isomeric tetrakis-(N-hexadecylpyridiniumyl)porphyrins and CdS nanoparticles

Using porphyrin amphiphiles TC16PyP(2), TC16PyP(3), and TC16PyP(4) as photo sensitizers, the interaction between amphiphilic porphyrins and colloidal C dS nanoparticles was studied by observing their absorption spectra, fluores cence spectra, and fluorescence lifetimes. The experimental results reveal that upon addition of CdS nanoparticles to a TC16PyP(3) or TC16PyP(4) solut ion, TC16PyP(3) or TC16PyP(4) is adsorbed onto the surface of the colloidal nanoparticles due to electrostatic action. The absorption spectra display the characteristic absorption of metalloporphyrin. Moreover, this adsorptio n also leads to red-shifted fluorescence spectra and the quenching of fluor escence emission. These changes are related to the formation of complexes. Nearly 90% of the fluorescence emission of 5 x 10(-6) mol/L TC16PyP(4) can be quenched with 6.8 x 10(-4) mol/L CdS colloid nanoparticles. Only 60% of the fluorescence emission of 5 x 10(-6) mol/L TC16PyP(3) can be quenched wi th 6.8 x 10(-4) mol/L CdS nanoparticles. The fluorescence quenching is attr ibutable mainly to static quenching. According to the fluorescence quenchin g curves, the apparent association constants of TC16PyP(4) and TC16PyP(3) w ith colloidal CdS nanoparticles are 1.42 x 10(3) (mol/L)(-1) and 6.76 x 10( 2) (mol/L)(-1),respectively. However, TC16PyP(2) does not adsorb onto the s urface of colloid nanoparticles due to its larger steric hindrance; its abs orption and fluorescence spectra are unchanged. (C) 2000 Academic Press.