Photoexcitation Dynamics of Thiophene-Fluorene Fluorophore in Matrix Encapsulation for Deep-Blue Amplified Spontaneous Emission

Precise control of the photophysical process is crucial to obtain efficient organic laser materials with high optical gain and low optical losses for the realization of organic lasers. Herein, we systematically demonstrated the photophysical process of steric thiophene-fluorene (MC6Cz-Th) fluorophore in an encapsulated polystyrene (PS) matrix for efficient deep-blue amplified spontaneous emission (ASE). MC6Cz-Th presents poor film morphology and low luminous intensity under solid conditions on account of strong intermolecular aggregation and photo-oxidation. Therefore, no ASE can be observed. Upon incorporation of this deep-blue fluorophore into an inert PS matrix, an intermolecular coupling of excited states was efficiently suppressed. To get further insights into the exciton behavior of MC6Cz-Th, a comparison of excited dynamics in a dilute solution, blend film, and neat film was performed using ultrafast transient absorption (TA) spectroscopy. The stimulate emission (SE) and photoinduced absorption (PA) decay curves of MC6Cz-Th in a dilute solution and blend film exhibit quite slow and perfect mirror shape located along the two sides beside the x-axis, indicating that the excitons originate from the same singlet that is dominated by the intrachain interaction. Moreover, the ASE threshold realized in the blend film was 44.3 μJ/cm2, highlighting its potential application in lasing materials.