Wavelength-selectivity in photochemical reaction between 1-alcohol and hydrogen-terminated silicon

We investigated a wavelength-selectivity in photochemical reaction between 1-alcohol and hydrogen-terminated silicon. Upon irradiation with UV lights with wavelengths shorter than 355 nm, 1-alcohol molecule attached onto the hydrogenated surface of single-side polished silicon (H-Si) to give a surface terminated with alkoxyl monolayer. In contrast, a 380 nm UV-irradiation could not produce an alkoxyl-terminated monolayer. Unlike the case of 1-alcohol, a wavelength-selectivity was not observed on H-Si in the presence of a neat 1-alkene, which was used as a control experiment. In our experiment, all of 1-alcohols and 1-alkenes were treated with sodium sulfate, and were then deoxygenated for at least 30 min through Freeze-Pump-Thaw (FPT) cycles. Both alkoxylation and alkylation of outermost silicon atoms were accelerated with increases in photon energy density of UV lights. We discuss this interesting phenomenon, that is, different photochemical reactivity of 1-alcohol, by the difference in monolayer formation mechanism between 1-alcohol and 1-alkene under UV light illumination.