Selenolates as Alternatives to Thiolates for Self-Assembled Monolayers:  A SERS Study

To determine whether selenolates are viable alternatives to thiolates for self-assembled monolayers (SAMs), the formation and oxidative stability of monolayers made from diphenyl diselenide (DPDSe) solution were assessed by surface-enhanced Raman spectroscopy. Upon adsorption, the diselenide bond is cleaved to form benzeneselenolate, analogous to formation of benzenethiolate monolayers from diphenyl disulfide (DPDS). DPDSe displaces benzenethiolate from gold, but DPDS does not displace benzeneselenolate. Competitive adsorption experiments show that adsorption of DPDSe is more favorable by ∼0.7 kcal/mol. Unlike benzenethiolate, the benzeneselenolate monolayer is unstable both in air and to UV light. Long-term exposure to air results in oxidation to protonated and deprotonated benzeneseleninic acid. Exposure to UV results in C−Se bond cleavage (analogous to C−S bond cleavage in benzenethiolate) and formation of SeO 2 and SeO 3 2 - . The higher adsorptivity of benzeneselenolate and its similar oxidative behavior to benzenethiolate suggests that selenolates are an attractive alternative to thiolates for building SAMs.