The Molecular Picture for Amplified Spontaneous Emission of Star-shaped Functionalized-Truxene Derivates

Organic optical gain materials for lasing are the basis for the organic solid-state lasers. However, the fundamental mechanism for Amplified Spontaneous Emission (ASE) is absent. Herein, three star-shaped molecules based on a truxene core with p-conjugated arms are studied to illuminate the influence of the molecular structure on ASE performance. We found that the three compounds demonstrated different ASE characteristics. The strong conjugated linkage in the molecular arms enhanced ASE, while the attenuated conjugated linkage deteriorates ASE for the given molecular structures. Based on the theoretical analysis, the conjugative coupling suppresses the low-frequency vibration, which is beneficial to the formation of effective “four-level” energy system for ASE. On the contrary, the poor conjugative coupling will bring out a mass of strongly elongated low-frequency modes, hence, continuous vibronic energy sublevels would ruin the molecular “four-level” energy system for lasing. Our study presented a clear picture to clarify the ASE mechanism explicitly and offer the valuable guidance for the design of new organic semiconductor optical gain materials.