Covalent Functionalization of Nanosheets of MoS₂ and MoSe₂ by Substituted Benzenes and Other Organic Molecules

Covalent functionalization has been effectively employed to attach benzene functionalities to MoS2 and MoSe2 nanosheets by the reaction with para-substituted iodobenzenes bearing -OCH3 , -H, and -NO2 as the substituents, where the electron-donating and electron-withdrawing power of the para substituent varies significantly. The functionalization is based on the formation of a C-S or C-Se linkage at the expense of the C-I bond on reaction of the iodobenzene with electron-rich 1T-MoS2 or 1T-MoSe2 . The degree of functionalization is in the range 4-24 % range, the value increases with the electron-withdrawing power of the para substituent. Semiconducting 2H-MoS2 and 2H-MoSe2 nanosheets can also be functionalized with iodobenzene by carrying out the reaction in the presence of a Pd0 catalyst. We have also carried out functionalization of 1T-MoS2 with pyrene, coumarin, and porphyrin derivatives. By using first-principles density functional calculations, we show that the bonding of the functional groups with the 1T phase is stronger than with the 2H phase. This is reflected in notable changes in the electronic structure of the former upon functionalization; a gap opens up in the electronic spectrum of the 1T phase. Functionalization with para-substituted benzenes leads to a change in the work function.