The Control of Conjugation Lengths and Steric Hindrance to Modulate Aggregation-Induced Emission with High Electroluminescence Properties and Interesting Optical Properties

• Published in: Chemistry : a European journal 2016-01, Vol.22 (3), p.916-924
• Main Authors: Xue, Miao-Miao, Xie, Yue-Min, Cui, Lin-Song, Liu, Xiang-Yang, Yuan, Xiao-Dong, Li, Yong-Xi, Jiang, Zuo-Quan, Liao, Liang-Sheng
• Format: Article
• Language: English
• Subjects: Acridine; Agglomeration; aggregation; Chemical synthesis; Chemistry; Conjugation; Devices; Electroluminescence; Emission; Emissions control; Emittance; Fluorene; Fluorescence; Light effects; luminescence; Optical properties; Phenyls; Rings (mathematics); spiro compounds; Steric hindrance; UV/Vis spectroscopy
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201503041

A series of novel AIE‐active (aggregation‐induced emission) molecules, named SAF‐2‐TriPE, SAF‐3‐TriPE, and SAF‐4‐TriPE, were designed and synthesized through facile reaction procedures. We found that incorporation of the spiro‐acridine‐fluorene (SAF) group, which is famous for its excellent hole‐transporting ability and rigid structure, at different substitution positions on the phenyl ring affected the conjugation lengths of these compounds. Consequently, we have obtained molecules with different emission colors and properties without sacrificing good EL (electroluminescence) characteristics. Accordingly, a device that was based on compound SAF‐2‐TriPE displayed superior EL characteristics: it emitted green light with ηc, max=10.5 cd A−1 and ηext, max=4.22 %, whereas a device that was based on compound SAF‐3‐TriPE emitted blue‐green light with ηc, max=3.9 cd A−1 and ηext, max= 1.71 %. These compounds also displayed different AIE performances: when the fraction of water in the THF solutions of these compounds was increased, we observed a significant improvement in the ΦF of compounds SAF‐2‐TriPE and SAF‐3‐TriPE; in contrast, compound SAF‐4‐TriPE showed an abnormal phenomenon, in that it emitted a strong fluorescence in both pure THF solution and in the aggregated state without a significant change in ΦF. Overall, this systematic study confirmed a relationship between the regioisomerism of the luminophore structure and its AIE activity and the resulting electroluminescent performance in non‐doped devices. Luminophores for organic LEDs: A series of new molecules, named SAF‐2‐TriPE, SAF‐3‐TriPE, and SAF‐4‐TriPE, that contain a quasi‐TPE (tetraphenylethene) subunit, were developed (see figure). These compounds displayed typical aggregation‐induced emission (AIE) properties, with the exception of the more weakly emitting SAF‐4‐TriPE. Additionally, non‐doped devices based on luminogens SAF‐2‐TriPE, SAF‐3‐TriPE, and SAF‐4‐TriPE were fabricated, and they displayed different electroluminescence properties with quantum efficiencies of 4.22, 1.71, and 1.42 %, respectively.