Aryloxy-benzothiadiazole-chalcone and aryloxy-benzothiadiazole-fluorene AIEE luminogens: Synthesis, photophysical properties, and electroluminescence evaluation

A previously described AIEEgen with architecture aryloxy-BTD-chalcone (BTD-CH) was used as a model for the synthesis of two analogs. The compounds were designed aiming either a higher donor-acceptor character (BTD-CH-TPA) or a higher structural rigidity (BTD-FL). They presented fluorescence ranging from cyan-green to yellow regions in solution, with large Stokes shifts and low fluorescence quantum yields. In contrast, in the solid state, both BTD-CH and its analogs presented intense fluorescence. BTD-CH-TPA and BTD-FL displayed aggregation-induced enhanced emission in acetone/water mixtures, with up to four-fold fluorescence enhancement upon aggregation, which represents a lower AIEE effect compared to BTD-CH. Monocrystal X-ray analysis of BTD-CH suggested a twisted conformation as well as the hampering of deleterious & pi;-& pi; interactions by the bent aryloxy group, which may be one of the reasons for its outstanding AIEE effect. BTD-CH and its analogs were tested as emitting layers for OLEDs and all devices displayed green electroluminescence at a low turn-on voltage (Von = 3 V). In addition, the compounds showed good charge conducting capacity, which favors their application as an emitting layer. The device fabricated with BTD-CH presented the best performance compared to those produced with the analogs. A reasonable maximum luminance (1577 cd m-2) and radiant emittance (9.95 & mu;W cm-2) were attained, which represents a good performance for a simple bilayer device.

Automated summary

Two analogs of AIEEgen, BTD-CH-TPA and BTD-FL, were synthesized and showed fluorescence ranging from cyan-green to yellow in solution. However, intense fluorescence was observed in the solid state for both BTD-CH and its analogs. The outstanding AIEE effect of BTD-CH is attributed to its twisted conformation and the hindrance of deleterious π-π interactions by the bent aryloxy group.