Low–threshold sky-blue gain medium from a Triazine-capped ladder-type oligomer neat film

A new solution-processable non-doped sky-blue organic laser gain medium has been developed based on triazine end-capped ladder-type oligo-(p-phenylene). The planar and symmetric conjugation of electron-withdrawing triazine moiety enables fine tuning of the emission from deep-blue to sky-blue with lowered LUMO energy level at no significant expense of optical gain properties. The emitter exhibits low amplified spontaneous emission (ASE) threshold of 41 nJ pulse⁻¹ (621 W cm⁻²), high maximum net gain coefficient of 73 cm⁻¹ and low loss coefficient of 6.45 cm⁻¹. Notably, a decent ASE phenomenon (at wavelength of 481 nm) can still be detected at film thickness of 42 nm with an ASE threshold of 99 nJ pulse⁻¹ (1.5 kW cm⁻²). These results suggest a prospective design concept for developing high-performance laser gain materials to address the challenge of electrically pumped organic lasers.