Enhancing Optical Gain Stability for a Deep-Blue Emitter Enabled by a Low-Loss Transparent Matrix

Abstract

Efficient organic gain media with high optical gain and good photostability are highly desirable for organic semiconductor lasers. To shed light on the rational molecular design, in this work, a novel deep-blue organic emitter consisting of a carbazole core substituted by a diphenylamine-functionalized triazine unit and two arms of bifluorene with flexible alkyl chains (denoted as C2) was designed and synthesized. Various basic photophysics and amplified spontaneous emission (ASE) characterizations were conducted with a particular focus to unravel the impact of the molecular structure on the photostability. Relatively low ASE threshold of 7.0 μJ/cm 2 , high net gain coefficient of 79.9 cm −1 (under 40-fold threshold pump fluence), and low optical loss coefficient of 7.0 cm −1 were recorded for C2 in neat films. For comparison, C2 was also dispersed into polystyrene (PS), a low-loss transparent matrix, with various ratios to form PS-C2 blend films. Among them, a 50 wt % PS-C2 blend film exhibited a high gain coefficient of 61.8 cm −1 and a low-loss coefficient of 5.4 cm −1 , manifesting enhanced gain properties in comparison with that of pure C2 sample (52.2 and 7.0 cm −1 ) under identical pump conditions (10fold threshold pump fluence). With simple high-ratio blending, the photostability and the film morphology stability under annealing conditions were found to be significantly enhanced, giving rise to highly stable optical gain properties. The optical gain properties of the PS-C2 blend films remained almost unchanged even upon harsh annealing treatment in ambient atmosphere. The results suggest an efficient strategy to enhance the photostability of organic gain media without sacrificing the optical gain properties by combining the merits of robust gain media and a low-loss transparent matrix for achieving efficient and stable organic semiconductor lasers.

Determination of the Best Empiric Method to Quantify the Amplified Spontaneous Emission Threshold in Polymeric Active Waveguides

“…To date, optical gain and optically pumped lasing have been demonstrated in many families of conjugated molecules and with a wide range on different resonators [ 20 , 21 ] and a first indication of lasing effect under electrical pumping has been recently reported [ 22 ]. In particular the organic systems showing optical gain can be divided in the two big families of neat films or blends of active molecules [ 2 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ,…”

Derivatives of diphenylamine and benzothiadiazole in optoelectronic applications: a review

“…2,1,3-benzothiadiazole derivatives are promising candidates for efficient solid-state emitters due to their strong electron-withdrawing effect, highly polarized properties, and easy crystallinity [22][23][24]. On the other hand, diphenylamine groups, due to the lone pair of electrons in nitrogen, have a high electron donation ability, thanks to which these derivatives are widely used in optoelectronics [25][26][27][28][29][30]. DPA as an electron donor increases the HOMO energy, while the use of an electron acceptor unit (e.g.…”

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

“…This is why the PLQY drastically reduced from 80% in the dilute solution state for single-molecule excitonic behavior to <5% in the neat spin-coated film. In this context, the effective suppression of the interchain interaction and aggregation by isolating fluorophore in a condensed structure is a promising method for achieving reasonably high PLQY of Th-based derivatives. , So far, many effective strategies have been proposed to realize the design idea, such as molecular self-encapsulation, , steric-substituted functionalization, − and physical blend strategy. − The former strategies of designing molecules require complex or refined synthetic conditions to deal with the problem of steric congestion in the process for a highly threaded molecular nano- and steric framework. In addition to these, matrix encapsulation is a general method for achieving optical gain properties by blending the dyes with inert polymer matrix, such as polystyrene (PS), polymethylmethacrylate (PMMA), polycarbonate (PC), or other similar polymers, which may result in similar lasing performance. , However, the details of the materials’ exciton dynamics in different states have been rarely explored before, and systematic investigation of the photoexcitation in the blended emissive system is vital to explore Th-based LCMs for light-emitting devices.…”