Designing High-Spin Small Organic Molecules for Optoelectronic Applications

Polycyclic hydrocarbons with open-shell character are extensively studied due to their tunable molecular scaffold and electronic properties. However, design strategies delineating control of the ground electronic state from closed-shell to open-shell diradical to polyradical character are not well studied. Here, we report indacenodinaphthothiophene isomers fused with five-membered carbonaceous rings and dicyanomethylene groups to show either a high-spin ground state or a large diradical and tetraradical character with small singlet-triplet energy gaps, not observed in these polycyclic hydrocarbons. Density functional theory calculation indicates the syn- and anti-configurations have closed-shell ground-state with a large singlet-triplet energy gap. However, the linear configuration displays pure open-shell diradical and tetraradical characters with small hexaradical characters. This study shows a novel design strategy of polycyclic hydrocarbons with a large polyradical character, compelling synthetic targets for magnetic and spintronics materials.