The lithium affinities of a series of heterocyclic compounds pyrrole, furan, thiophene and pyridine in their low-lying excited triplet state: A DFT based comparative study

Gas phase lithium affinities(ΔEs) and transition energies of a series of heterocyclic compounds (pyrrole, furan, thiophene and pyridine) and their Li complexes have been performed using density functional theory (Becke, Lee, yang and parr [B3LYP]) method using 6-311G(d,p) basis set with complete geometry optimization in their low-lying excited triplet state. As in the case of ground states, the gas phase Li complex formation turns out to be exothermic case and the local stereochemical disposition of the Li is found to be almost the same in each case. It is seen that lithium affinity is highest for pyridine(-0.08 hartree) and lowest for pyrrole(-0.0178 hartree). Computed lithium affinities are also sought to be correlated with the number of computed system parameters such as the net computed charge on the hetero atoms of the free bases and Li complexes, charge on the Li of the Li complexes and the computed hardness of the free bases in their relevant excited states. The lithium induced shifts(LIS) are in general red shifts for the lowest excited triplet states.