Electronic structure and near-IR transitions of FcC 2R and FcC 4R dyads

Abstract

This paper describes the orbital configuration which provides a basis for the understanding of the electronic structure and spectroscopic properties of 17e and 18e FcC 2R and FcC 4R dyads, where R is H, 1-naphthyl, 9-anthryl, 3-pyrenyl, perylenyl. DFT calculations show that destabilisation of the ferrocenyl π orbitals upon binding a C CR group to a Cp ring leads to the metal-based a 1 orbital dropping below the e 1-a so that the frontier orbital configuration is ( e 2 ′ -a, π ) 2 ( e 2 ′ -b,metal ) 2 ( e 1 ′ -a, π ) 2 , (a 1, metal) 2. The contribution of the aryl group to the π e 2-a and e 1-a orbitals varies with the annelation of the ring. The LUMO is aryl based. The calculations are consistent with the spectroscopic data for the 18e species. Oxidation to the 17e cations does not change the orbital configuration but the orbital energies are lowered by the positive charge centred on the Fe. A strongly solvatochromic transition in the near-IR, a signature for the 17e cations, is best described as an LMCT transition but the contribution of C 2R and C 4R to the donor and acceptor levels depends on the ionization energy of the aryl π orbital. LMCT energies decrease from FcC 2R to FcC 4R dyads.