Orbital inversion mechanisms hidden in strongly correlated radical systems

Orbital inversion in organic radical systems is of interest in multiple domains such as spintronics, luminescence, and chemical reactions but requires to comprehend its mechanisms. Here, we reveal an implicit but significant factor for orbital-inverted radical systems. Within the framework of the Hubbard model, the inversion can emerge from nearest-neighbor coulombic repulsion between two electrons having the same spin, which necessitates the fulfillment of charge-transfer properties and chlorine atom substitution. These conditions can also be utilized to explain previous experimental observations where some of radical analogues exhibit orbital inversion while others remain devoid of it. We also discuss the underlying picture and the phase diagram of the orbital inversion, providing a perspective on π-conjugated systems and double inversion. Our results establish a practical approach to nanoscale control of magnetic and optoelectronic properties in radical-based structures.