1365541-02-1Relevant academic research and scientific papers
Synthesis of Fluorene-Bridged Arylene Vinylene Fluorophores: Effects of End-Capping Groups on the Optical Properties, Aggregation Induced Emission
Zhang, Guo-Feng,Chen, Tao,Chen, Ze-Qiang,Aldred, Matthew P.,Meng, Xianggao,Zhu, Ming-Qiang
, p. 939 - 947 (2015)
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-diphenylvinyl)phenyl (F1-(1,2)-HTPE) were synthesized and compared to the tetraphenylethene analogue (F1-TPE). Both F1-(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 F1-(2,2)-HTPE and 437 nm for F1-(1,2)-HTPE. The fluorescence quantum yields (Φ;F) of F1-(2,2)-HTPE (?F=35.1 %) and F1-(1,2)-HTPE (?F=26.2%) were found to be higher in solution compared to the near quenching of F1-TPE (?F=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 another method to decrease the AIE characteristics, in a similar manner to the commonly known ?phenyl-locking?. Non-polar triphenylethenes are poorer AIE materials than their tetraphenylethene analogues. Replacing the hydrogen 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 (?F=0.12%). X-ray crystallographic analysis of F1-TPAN indicates that the introduction 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. Four different arylene vinylene substituents attached to the fluorene were synthesized, and the disparities of AIE-effect of these compounds were discussed. The cyano-groups in F1-TPAN will not only reduce the steric congestion of the peripheral phenyl rings, but also appreciably improve the molecular cohesion ability via multiple C-H?N interactions.
Fluorescence quenching and enhancement of vitrifiable oligofluorenes end-capped with tetraphenylethene
Aldred, Matthew P.,Li, Chong,Zhang, Guo-Feng,Gong, Wen-Liang,Li, Alexander D. Q.,Dai, Yanfeng,Ma, Dongge,Zhu, Ming-Qiang
, p. 7515 - 7528 (2012/06/01)
We report the synthesis of novel amorphous fluorene-based fluorophores that have been end-capped with tetraphenylethene (TPE). Although in the solid state the fluorophores show bright cyan fluorescence with high (68%) photoluminescence quantum efficiency (PLQE), strong fluorescence quenching is observed in solution with low PLQE values ranging from 0.3% to 2.1%. When the fluorophores were added to a 90% water-THF solvent mixture nanoparticles were formed, which was confirmed by Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM). Subsequent fluorescence measurements reveal that all the fluorophores exhibit aggregation induced emission (AIE) with high PLQE (41%). We have carried out a comparative study of 5 fluorene-based TPE materials (F(1-5)TPE), in which the fluorene core is extended, and investigated their thermal, optical, electrochemical and electroluminescence properties. From fluorescence quantum yield data we have discovered that the AIE effect decreases as the fluorene core increases both in the nanoparticle and in the solid state. Thermal analysis reveals that all fluorophores are amorphous with high thermal stabilities. Potential application in solid state vapour sensing has been demonstrated using dichloromethane that shows "on" and "off" fluorescence behaviour. Finally, Organic Light Emitting Diodes (OLEDs) have been fabricated with device configuration ITO/PEDOT/F(1-5)TPE/TPBi/LiF/Al. The best OLED device that incorporates F1-TPE as the emitter exhibits a turn-on voltage of 5.8 V, Lmax = 1300 cd m-2, ηP,max = 1 lm W -1 and ηC,max = 2.6 cd A-1.
