Donor–Acceptor Type Pendant Conjugated Molecules Based on a Triazine Center with Depressed Intramolecular Charge Transfer Characteristics as Gain Media for Organic Semiconductor Lasers

• Published in: Chemistry : a European journal Vol. 26; no. 14; pp. 3103 - 3112
• Main Authors: Liu, Xu, Sang, Ming, Lin, He, Liu, Chengfang, Zhang, Jialing, Yi, Jianpeng, Gao, Kun, Lai, Wen‐Yong, Huang, Wei
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 09.03.2020; Wiley Subscription Services, Inc
• Subjects: amplified spontaneous emission; Annealing; Capping; Carbazole; Carbazoles; Charge transfer; Chemistry; Chemistry, Multidisciplinary; Electrical properties; Fluorene; Fluorescence; intramolecular charge transfer; Lasers; Optical properties; organic semiconductor lasers; organic semiconductors; pendant conjugated molecules; Physical Sciences; Science & Technology; Semiconductor lasers; Spontaneous emission; Thermal stability; Triazine; organic semiconductors; DESIGN; intramolecular charge transfer; OPTICAL GAIN; amplified spontaneous emission; pendant conjugated molecules; organic semiconductor lasers; ELECTROLUMINESCENCE
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201904548

A set of fluorene‐capped pendant conjugated molecules (T‐m and T‐p), which consist of a triazine center with three carbazole substituents as the donor–acceptor (D‐A) type pendant structure, were designed, synthesized, and investigated as gain media for organic semiconductor lasers (OSLs). In particular, varying the capping positions of the fluorene units on the pendant core structures results in significantly different intramolecular charge transfer (ICT) properties, where T‐m manifested depressed ICT characteristic and high fluorescence quantum yield. The lowest amplified spontaneous emission (ASE) threshold in neat films was recorded as 1.9 μJ cm−2 for T‐m and 83.8 μJ cm−2 for T‐p, which indicated that the depressed ICT characteristics in the case of T‐m help to enhance the ASE properties. Remarkably, the ASE threshold remained almost unchanged and the ASE spectra showed very small shifts (within 1 nm) for T‐m with film samples annealed up to 180 °C in open air. In contrast, its linear counterpart 2FEtCz‐m showed a clearly increased ASE threshold upon annealing above 100 °C. The results suggest that the selective construction of conjugated pendant molecules with depressed ICT characteristics is beneficial for finely modulating the optical and electrical properties as well as improving the thermostability and photostability, which manifests the great potential as a robust gain media for OSLs. Organic semiconducting lasers: A set of novel fluorene‐capped pendant conjugated molecules (T‐m and T‐p) were designed, synthesized, and investigated as gain media for organic semiconductor lasers. Varying the capping positions of the fluorene units on the pendant core structures results in significantly different intramolecular charge transfer (ICT) properties. No clear donor–acceptor characteristics were observed in T‐m, whereas T‐p exhibited distinct ICT properties according to the experimental results and theoretical calculations. The results demonstrated that selective construction of the pendant conjugated molecules with depressed ICT characteristics helps to achieve robust gain media with excellent optical gain properties and enhanced thermostability and photostability as well as fine‐tuning the electrical behaviors.