Synthesis of Fluorene-Bridged Arylene Vinylene Fluorophores： Effects of End-Capping Groups on the Optical Properties, Aggregation Induced Emission

• Published in: Chinese journal of chemistry 2015-08, Vol.33 (8), p.939-947
• Main Authors: Zhang, Guo-Feng, Chen, Tao, Chen, Ze-Qiang, Aldred, Matthew P., Meng, Xianggao, Zhu, Ming-Qiang
• Format: Article
• Language: English
• Subjects: 2,3,3‐triphenylacrylonitrile; 3-triphenylacrylonitrile; aggregation-induced emission; fluorene; tetraphenylethene; triphenylethene; 乙烯合成; 光学性质; 发光; 封盖作用; 桥联; 聚芴; 荧光团; 诱导
• ISSN: 1001-604X; 1614-7065
• DOI: 10.1002/cjoc.201500240

We have synthesized a series of fluorene-based fluorophores, in which a central fluorene core has been modified with different peripheral arylene vinylene substituents that are able to activate aggregation-induced emission （AIE） characteristics. 9,9-Dioctylfluorene doubly end-capped at the 2,7-positions with triphenylethene groups, such as 4-（2,2-diphenylvinyl）phenyl （F1-（2,2）-HTPE） and 4-（1,2-dipbenylvinyl）phenyl （F1-（1,2）-HTPE） were synthesized and compared to the tetraphenylethene analogue （F1-TPE）. Both FI-（2,2）-HTPE and F1-（1,2）-HTPE glow with a deep blue fluorescence in THF solution with emission maxima （λem） of 426 and 403 nm, respectively. The λem slightly red-shifts in the solid-state to 458 nm for F 1-（2,2）-HTPE and 437 nm for F 1-（1,2）-HTPE. The fluorescence quantum yields （ΦF） of F1-（2,2）-HTPE （ΦF=35.1%） and FI-（1,2）-HTPE （ΦF=26.2%） were found to be higher in solution compared to the near quenching of F 1-TPE （ΦF = 0.1%）. Consequently, this results in weaker AIE-stability of F1-（2,2）-HTPE （αAIE= 1.5） and F1-（1,2）-HTPE （αAIE=1.9） compared to F1-TPE （αAIE=125）, suggesting that four phenyl groups are necessary for efficient AIE-activity of these fluorene bridged arylene vinylene type materials In addition, decreasing the steric hindrance around the arylene vinylene moiety by removal of a phenyl ring is an- other method to decrease the AIE characteristics, in a similar manner to the commonly known ＂phenyl-locking＂. Non-polar triphenylethenes are poorer AlE materials than their tetraphenylethene analogues. Replacing the hydro- gen atom of F1-（2,2）-HTPE with a cyano group affords fluorene end-capped with 2,3,3-triphenylacrylonitrile （F1-TPAN）, which boosts the AIE-effect to αAIE=90.5 and red-shifts the solid-state emission （λem=528 nm） with near quenching in THF solution （ΦF= 0.12%）. X-ray crystallographic analysis of F1-TPAN indicates that the intro- duction of cyano groups can not only diminish the intramolecular steric hindrance in comparison of F1-TPE, but also improve the molecular cohesion ability via multiple C--H...N interactions.