High Efficiency D-A Structured Luminogen With Aggregation-induced Emission And Mechanochromic Characteristics: Molecular Design, Synthesis, And Photophysical Properties

Due to their unique photophysical and intra-molecular charge transfer(ICT) properties, conjugated molecules with electron donor-acceptor(D-A) architectures are of growing interest for a wide variety of applications in optoelectronic devices, solar energy conversion, micro-environmental changes detection, organic lasers, cellular imaging, and so on. Additionally, solid emitters showing mechanofluorochromism are promising for various applications in optical storage, chemical and stress sensors, security papers, optoelectronic devices, etc.However, many conventional luminogens suffer from the notorious aggregation-caused quenching(ACQ) problem due to the formation of such detrimental species as excimers and exciplexes in the solid state. However, in practice, luminogens are normally used in the solid state(for example, solid films), therefore aggregation is inevitable. In sharp contrast to traditional luminogens, the AIE luminogens are nonemissive when dissolved in good solvents but become highly emissive upon aggregation in the solid state. Therefore, the design and synthesis of novel AIE molecules with D-A structure and mechanochromic characteristics are of great scientific significance and promising technical applications.Firstly, we synthesized 1CN2BN(M) luminogens based on 1-cyano-trans-1,2-bis-(4-methyl-biphenyl)-ethylene and diphenylamine(4-methyldiphenylamine). Both compounds show interesting ICT property and high quantum efficiency(51.7%, 25.3%). 1CN2 BN also displays mechanochromic nature with a red shift of 25 nm upon mechanical stimuli. Additionally, two three-layered EL devices were fabricated using 1CN2 BN as emitting layer. The device II, with the configuration of ITO/NPB/MADN:DPA-CS/Alq3/Liq/Al, performs better giving Lmax, CEmax, PEmax, and EQE of 17750 cd/m2, 14.16 cd/A, 4.53 lm/W, and 5.08%, respectively.Secondly, we synthesized CZ2 TPAN based on TPAN. Similar to 1CN2 BN, CZ2 TPAN shows typical ICT and AIE characteristics, and moreover high solid-state efficiency of 65.3% as well as distinct mechanochromism with a remarkable shift of 41 nm.