Control in spin-delocalization into the 2-substituted π-systems in 3-oxophenalenoxyl neutral radicals: evaluation by their dimeric structures and DFT calculations

3-Oxophenalenoxyl derivatives, neutral π-radicals having two oxygen atoms at 1,3-position on a phenalenyl skeleton, possess most of their spin densities at the two oxygen atoms and the 2-position, featuring in easy dimerization at the 2-position. For the decrease in spin density at the 2-position by invoking spin-delocalization into the 2-substituted π-systems, we have designed 2-thienyl-3-hydroxyphenalenone derivatives as synthetic precursors of neutral π-radicals, and conducted their oxidation reactions by using a variety of oxidants. The chemical structures of the dimer obtained were unambiguously determined by FABMS, IR, and NMR spectra with help of density functional theory calculations, showing the formation of the bonds on the thienyl moieties. These observations and DFT calculations illustrate the occurrence of a considerable amount of spin-delocalization into the 2-substituted-thienyl moieties from the 3-oxophenalenoxyl skeletons.