Manipulating organic triplet harvesting in regioisomeric microcrystals

Abstract

A big step towards manipulating organic triplet harvesting has been taken in three N-benzoyl-carbazole regioisomeric microcrystals (L-(p,m,o)Br) which consist of a –Br group at the para (p)/meta (m)/ortho (o) positions of the phenyl ring, respectively. The manipulation is demonstrated by blue thermally activated delayed fluorescence (TADF) emission in L-pBr, blue and yellow dual room temperature phosphorescence (RTP) emissions with different lifetimes in L-mBr, and ultralong yellow RTP in L-oBr. The effect of the –Br group was verified in molecular excited electronic structures and packing modes upon crystallization. Single crystal analysis and theoretical calculations reveal that exciton structures in the L-(p,m,o)Br dimers are strongly influenced by the bromine substitution positions, leading to different ways to harvest triplet excitons. As a simple and feasible strategy, taking advantage of the substitution position effect is promising in the manipulation of organic triplet excitons to achieve multifarious applications based on triplet exciton properties.