Multi-responsive And Optical Properties Of Salicylidene Schiff Bases

Salicylidene Schiff bases are widely used as metal sensors, stimulate responsive intelligent materials, optical materials due to their simple synthetic procedures, wide range of modifications, easy coordination with metal ions and multi-stimulus response characteristics. Herein, we designed and synthesized a series of Salicylidene Schiff derivatives and explored their application in ion recognition, self-assembly, mechanochromic properties, respectively.First, a multi-metal colorimetric and fluorescent sensor based on Schiff base was synthesized. This sensor could simultaneously detect and differentiate three transition metal ions through fluorogenic(Zn2+) and chromogenic(Cu2+, Zn2+ and Ni2+) methods in real time with low detection limit in aqueous medium. The cell imaging experiment further confirmed that the sensor could be used for monitoring trace Zn2+ in living cells. On the other hand, the corresponding colour changes can be directly discriminated the three analysts by “naked eye”.Second, the traditional ion sensing in solution state is hardly to meet the actual demand. In the paper, we tried to materialize the optical probe molecules. By modifying the probe with long alkoxy chains and fluorophore(cyanostyrene), we successfully designed two new gelators HBPA and HNPA with AIE characteristics(Aggregation-induced enhanced emission). Both of them could form gels in a variety of common organic solvents through multistage self-assembling. We studied the gel structure in detail through gel capacity test and morphology observation, etc. Theses stable supramoleculear gels was found to be self-assembled by hydrogen bonding and other weak interactions. Moreover, HBPA was an anion sensor, it could recognize fluorine ion in solution state and gel state, specificity.At last, it was found that HNPA is not only one kind of soft gels, it was also a kind of piezochromic materials. The larger conjugate structure naphthalene salicylaldehyde was introduced to HNPA molecule. The introduction make the molecular structure more distortion and the molecule stacking in very loose way with holes among the net work. The stimulation of the pressure changed the way of molecular packing, leads to the enhancement of the intermolecular conjugate, resulting in strong red shift in fluorescent spectrum. In addition, the mechanochromic behavior of HNPA is reversible by simply repeating the grinding–vapor fuming process. So the force just changed the physical way of molecular packing. Obviously, HNPA molecular belongs to one kind of typical piezofluorochromic materials.