Luminescent columnar liquid crystals based on AIE tetraphenylethylene with hydrazone groups bearing multiple alkyl chains

A series of novel tetraphenylethylene aromatic acylhydrazone derivatives 11, 12 and 13 with 4, 8 or 12 alkyl chains were designed and synthesized in yields of 82-85%. Studies on the mesomorphic properties suggested the ordered hexagonal columnar mesophase for compounds 11, 12 and 13. The increase in the number of alkyl chains was favourable for decreasing the phase-transition temperatures and extending the mesophase temperature range. Further, samples 11, 12 and 13 presented an excellent AIE effect. The fluorescence intensities increased by 70, 84 and 43 times for samples 11, 12 and 13, respectively. The absolute fluorescence quantum yields were 18.7%, 27.4% and 23.8% in solid films at room temperature and 6.7%, 24.2% and 17.3% in the mesophase. These results suggested that the number of alkyl chains greatly influenced the fluorescence emission and sample 12 with 8 alkyl chains exhibited the strongest fluorescence emission. Sample 12 also displayed the electroluminescence performance on OLED device.