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 (ΔEST) 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 ΔEST. 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 ΔEST 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.