Structure-lock induced phosphorescence lifetime enhancing of (9H-carbazol-9-yl)(phenyl)methanone: An organic phosphorescent materials

Abstract

Different molecular design strategies have been performed to study purely organic materials with room-temperature phosphorescence (RTP) by suppressing nonradiative deactivation and facilitating intersystem crossing. In this work, a synthetic strategy based on CPM ((9H-carbazol-9-yl)(phenyl)methanone) has been performed to achieve long lived RTP by immobilizing the torsion of benzophenone moiety and forming a six-membered heterocyclic ring containing nitrogen element. This synthesized locked-CPM (8H-indolo[3,2,1-de]phenanthridin-8-one) with higher rigidity has planar configuration both in the singlet state and the triplet state, whose locking configuration effectively inhibits the twist intramolecular charge transfer (TICT) of CPM and significantly reduces the energy gap between the singlet and triplet states to 0.89 ev. This change facilitates intersystem crossing and the generalization of triplet excitons. By fitting the phosphorescence decay curves, we demonstrate that the phosphorescence lifetime of the locked-CPM has increased by nearly forty times compared with that of the CPM, indicating that the presented strategy will bring insight into the developing long lived RTP materials. It is noted that suppress the vibration and torsion of molecular and reduce the energy gap between single-triplet states will favors of long phosphorescence lifetime.