Low-Threshold Non-Doped Deep Blue Lasing from Monodisperse Truxene-Cored Conjugated Starbursts with High Photostability.

Abstract

Herein, the photophysical, morphological, optical gain characteristics of a set of trigonal monodisperse starburst conjugated macromolecules (Tr1-Tr4) have been systematically investigated in order to elucidate the influence of the molecular structures on their optoelectronic performance. With increasing the oligofluorene arm length, absorption spectra were red-shifted progressively, whereas an increase in photoluminescence quantum yields (PLQYs) and optical gain coefficients, and a corresponding reduction in amplified spontaneous emission (ASE) thresholds and loss coefficients were observed for Tr1-Tr3 except for Tr4. The results indicate that the effective conjugation length become saturated for Tr3 in this system. Impressively, the resulting molecules manifested very low ASE thresholds (4.4-11.6 μJ cm-2 ) with high photostability, as well as high thermal stability. One dimensional distributed feedback (DFB) lasers exhibited a minimum lasing threshold of 10.38 nJ pulse-1 (0.86 kW cm-2 , 4.325 μJ cm-2 ) for Tr3. It should be emphasized that the ASE threshold of Tr1-Tr4 was nearly unchanged from room temperature to 200 °C. The results suggest that this kind of truxene-cored conjugated starbursts with high photostability and low lasing thresholds are rather promising gain media for organic semiconductor lasers.