Title: Computational Design of Boron-Free Triangular Molecules with Inverted Singlet-Triplet Energy Gap

Abstract: A novel, computationally designed, class of triangular-shape organic molecules with an inverted singlet-triplet (IST) energy gap is investigated with the aid of ab initio methods of electronic structure theory. The considered molecular systems have a form of cyclic oligomers and their common feature is electronic conjugation localized along the molecular rim. Analysis of vertical transition energies from the electronic ground state, as well as from the lowest excited singlet and triplet states of selected molecules, is conducted. The results underscore the significance of optimizing excited-state geometries in theoretical models to accurately describe the optoelectronic properties of the IST molecules, particularly in relation to their applications in OLEDs.