TUNING THERMALLY ACTIVATED DELAYED FLUORESCENCE IN 1,8-NAPHTHALIMIDE DERIVATIVES BY DONOR VARIATION

Abstract

Donor-acceptor compounds based on N-substituted naphthalimide as an acceptor unit integrated with diverse range of amine-based donors via an ortho-phenyl linker or direct C4 naphthalimide substitution were designed for realizing thermally activated delayed fluorescence (TADF) characteristics. Effects of change of dihedral angles between planes of donor and acceptor units on excitations were studied to relate with frontier orbital overlap which directly impact the singlet-triplet splitting (𝛥𝐸𝑆𝑇). Remarkably, high spin-orbit coupling (<S1|HSOC|T1>) values were obtained for a compound containing bromo substituent (KJ-2-Aʹ) (> 10 cm-1) in perfect balance with small ΔEST value (0.103 eV), which strongly indicates higher probability of accelerated rate of reverse intersystem crossing (𝑘𝑟𝐼𝑆𝐶), hence is expected to emerge as an excellent TADF emitter. Other electronic properties like ionization potential, electron affinity, reorganization energies were also calculated to study electron-hole injection and charge transport abilities in OLEDs.