Rational Design of Organic Emitters with Inverted Singlet–Triplet Gaps for Enhanced Exciton Management

In organic light-emitting diodes (OLEDs), the pursuit of efficient molecular emitters has led to the development of thermally activated delayed fluorescence (TADF) molecules. While TADF compounds have promising properties, they face challenges such as energy gap constraints and uphill exciton transfer. Inverted emitters (INVEST) offer a novel solution with an inverted singlet-triplet energy (Δ<i>E</i>_ST) gap, enabling efficient utilization of excitons. This study examines the design and computational analysis of an array of molecules, including 23 INVEST emitters and remaining with positive energy gaps. Within the STEOM-DLPNO-CCSD framework, we explore the role of various molecular fragments in determining Δ<i>E</i>_ST. We also assess the importance of dynamic spin-polarization (DSP) obtained via the Pariser-Parr-Pople (PPP) scheme in energy gap determination. Exciting trends emerged from our results, with pentalene-containing compounds consistently manifesting negative Δ<i>E</i>_ST values while their naphthalene counterparts exhibited contrasting behavior. Moreover, we observed a negative DSP correlates with inverted singlet-triplet gaps. Overall, this research advances OLED materials through molecular design and computational analysis, offering avenues for optimizing exciton management and enhancing device performance.