Effects of functionalization on the electronic and absorption properties of the smaller diamondoids: a computational study

Abstract

Functionalized diamondoids show great potential as building blocks in view of their optoelectronic, catalytic, and therapeutic applications. In this work, we report the effect of functionalization on the electronic and absorption properties of the first two lower diamondoids, adamantane and diamantane, respectively. We performed quantum mechanical calculations within the framework of density functional theory (DFT) and time-dependent (TD-DFT) theory for the mono-, di-, and tetra-substituted smaller diamondoids. Bandgap tuning is made through the push (electron-donating) and pull (electron-withdrawing) doping, external substitution at the C-H site, which reduces the band gap of diamondoids significantly. The stability of pristine and the functionalized smaller diamondoids is also studied by calculating the ionization potentials and affinity energies. Employing TD-DFT method at the level of PBE1PBE theory, the UV absorption spectra of the functionalized smaller diamondoids were calculated and discussed. While the lowest allowed and most intense transition energies are significantly reduced with the increasing number of pull-type functional groups, the push-type groups slightly increase those energies. Synopsis DFT and TD-DFT investigations of pristine and functionalized smaller diamondoids are presented. Tertiary sites (-C-H) of the smaller diamondoids are chosen for the functionalization by the pull and push type groups. Band gaps, vertical excitation energies, ionization potentials and electron affinities are calculated at the high-level of PBE1PBE theory with 6-31+G(d,p) basis set. Pull-type functional groups show a greater effect on the electronic and absorption properties of smaller diamondoids, compared to the push-type groups.