Modulation of Amplified Spontaneous Emissions between Singlet Fluorescence and Triplet Phosphorescence Channels in Organic Dye Lasers

Abstract

AbstractOrganic gain materials (OGMs) currently used in dye lasers and organic thin‐film amplifiers are limited to singlet‐fluorescence molecules. Although heavy‐metal‐containing phosphorescent emitters enable highly efficient organic light‐emitting diodes, phosphorescent OGMs capable of light amplification by stimulated emission from triplet states remain largely unexplored. Demonstrated herein is the first phosphorescent dye laser from a pure organic luminescent rotor (1), composed of electron‐donating sulfide‐substituted difluoroboron (SBF2) and electron‐accepting nitrobenzene (NB) moieties. Furthermore, modulation of amplified spontaneous emissions (ASEs) between singlet fluorescence and triplet phosphorescence channels is achieved by adjusting the relative rotation (dihedral angle θ) of the donor and acceptor moieties. Theoretical calculations and experimental results clarify that free and restricted rotor rotation regulates the T2 state below and above the S1 state, thus switching on and off the intersystem crossing from S1 to the high‐lying T2 for phosphorescence and fluorescence, respectively. Based on this strategy, methyl groups are added on the NB moiety to increase the steric hindrance in 2, leading to tunable phosphorescence and/or fluorescence ASE. The results extend the scope of organic dye lasers and provide a strategy to develop phosphorescence OGMs capable of amplifying light through ASE from the triplet state.