Light harvesting in silicon (111) surfaces using covalently attached protoporphyrin IX dyes

We report the photosensitization of crystalline silicon via energy transfer using covalently attached protoporphyrin IX (PpIX) derivative molecules at different distances via changing the diol linker to the surface. The diol linker molecule chain length was varied from 2 carbon to 10 carbon lengths in order to change the distance of PpIX to the Si(111) surface between 6 A and 18 A. Fluorescence quenching as a function of the PpIX–Si surface distance showed a decrease in the fluorescence lifetime by almost two orders of magnitude at the closest separation. The experimental fluorescence lifetimes are explained theoretically by a classical Chance–Prock–Silbey model. At a separation below 2 nm, we observe for the first time, a Forster-like dipole–dipole energy transfer with a characteristic distance of R0 = 2.7 nm.