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 MoSe₂. The degree of functionalization is in the 4%-24% range, the value increasing 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 the Pd(0) catalyst. We have also carried out functionalization of 1T-MoS₂ with pyrene, coumarin and porphyrin derivatives. Using first-principles density functional calculations, we show that bonding of the functional groups with 1T phase is stronger than with the 2H phase. This gets reflected in notable changes in the electronic structure of the former upon functionalization; a gap opens up in the electronic spectrum of 1T phase. Functionalization with para-substituted benzenes leads to a change in the work function.