Experimental and theoretical insights into the sequential oxidations of 3π-2spiro molecules derived from oligophenylenes: A comparative study of 1,2-b-DiSpiroFluorene-IndenoFluorene versus 1,2-b-DiSpiroFluorene(tert-butyl)4-IndenoFluorene

Cyclic voltammetry and differential pulse voltammetry have shown too distinct behaviours in the sequential oxidation processes of two closely related compounds, namely 1,2-b-DiSpiroFluorene-IndenoFluorene (1,2-b-DSF-IF) and 1,2-b-DiSpiroFluorene(tert-Butyl)4-IndenoFluorene (1,2-b-DSF(tBu)4-IF). 1,2-b-DSF-IF is oxidized after a reversible one-electron transfer and a subsequent irreversible two-electron transfer. In contrast, 1,2-b-DSF(tBu)4-IF undergoes three well separated chemically reversible one-electron processes. Spectroelectrochemical monitoring of the gradual oxidation of the compounds points to a first oxidation centred on the indenofluorenyl core for both molecules. Consistent with the different electrochemical behaviour, the spectroelectrochemical data after the first oxidation is very different for both compounds and points to a specific electronic structure. This is further studied theoretically by DFT calculations of the molecules in their neutral, cationic and dicationic state which suggest an electronic reorganization in the dication 1,2-b-DSF(tBu)4-IF2+.