Ladder-type materials with D–π–D architectures as robust gain media for organic lasers

Abstract

A new series of ladder-type materials with donor–π–donor (D–π–D) architectures and diphenylamine (DPA) end-cappers, namely LBDT, LIDT and LIDTT, were developed as robust gain media for organic lasing. Ladder-type compounds can greatly increase both thermal and optical stabilities and impart well-defined physical characteristics because of the rigid and co-planar framework. Extensive studies on the thermal gravimetric analysis (TGA), fluorescence transients and amplified spontaneous emission (ASE) measurements offered a chance to fully investigate the influence of the D–π–D ladder-type architectures on the photophysical and the optical gain characteristics. By adjusting the D–π–D ladder-type structure, large Stokes shifts were observed and the emission from green to orange was achieved. LBDT, LIDTT and LIDTT possessed the threshold of 6.8, 10.4 and 9.4 μJ cm⁻² with the ASE peaks at 522, 555 and 563 nm, respectively. Besides, ASE behaviors of LBDT and LIDTT were still detected even by annealing at 225 °C and LBDT demonstrated the best ASE thermal stability among these molecules. Meanwhile, low loss coefficients of 6.46 and 13.47 cm⁻¹ were determined for LBDT and LIDTT, respectively. Owing to the superior comprehensive physical characteristics of LBDT, organic lasers based on LBDT were fabricated to investigate its lasing behaviors, demonstrating the low lasing threshold of 1.38 kW cm⁻². Our work indicates that the creation of ladder-type architectures is crucial to the evolution of gain materials for organic lasers, providing an attractive platform for unraveling the relationships between the particular ladder-type molecular structures and the lasing functions.