The impact of atomic substitution on the photophysics of contorted hexabenzocoronene derivatives

The photophysical properties of organic semiconductors are strongly influenced by the spin states, lifetimes, populations, and energies of the lowest photoexcited species (S1 or T1). By favoring or limiting the rate of intersystem crossing (ISC), the relative population and lifetime of singlet and triplet excitons can be controlled through molecular design. The incorporation of heavy atoms, such as transition metals, have been reported to enhance spin-orbit coupling in organic systems. Here, we explore the role of peripheral moieties with heteroatoms on the photophysical properties of contorted hexabenzocoronene (cHBCs) derivatives. These chemical alterations may impose sterics or enhance spin-orbit coupling, significantly increasing the rate of ISC. With benzofuran moieties, cTBFDBC exhibits the highest degree of molecular contortedness in the series, which is correlated with a high rate of ISC. With much heavier benzothiophene moieties, cTBTDBC uniquely exhibits room temperature and higher phosphorescence yield compared to cTBFDBC, which we correlate to a high degree of spin-orbit coupling induced by the heavy sulfur atom. These findings offer valuable guidelines for enhancing the optoelectronic properties of cHBCs using simple molecular substitution approaches.