Design,Synthesis And Properties Of Tetraphenylethenes Which Embedded In The Calix[4]arenr And Pillar[5]arene’s Skeletons

Tetraphenylethene(TPE)and its analogues are luminogenic molecules with aggregation-induced emission(AIE)nature.In contrast to the fluorophores showing notorious aggregation-caused quenching(ACQ)characteristics,the AIE luminogens emit efficiently in concentrated state due to the aggregation.Embedding tetraphenylethenes in some functional molecules not only could enhance the functionality of the molecules,but also could utilize the conformation change of the functional molecules to alternate the conformation of the TPEs.We embedded the TPE unit in calix[4]arene and pillar[5]arene scaffolds utilizing the diphenylmethane nature of the meso position of these two molecules.The relationship between luminescence properties and conformations was studied.In the first part,two novel 1,1-diphenylmethylidene decorated calix[4]arenes,(Calix-DPE(OCH3)4 and Calix-DPE(OH)4),were designed and prepared.The tetraphenylethene(TPE)unit was embedded in the calix[4]arene skeleton,so the conformation of tetraphenylethene unit was significantly affected by the conformation of calix[4]arene which in turn affects the luminescent properties of TPE.In the Calix-DPE(OCH3)4,the dihedrals between the phenyl rings and the plane of C=C bond are around 40-60° due to the partial cone conformation of calix scaffold,which leads to the minimal energetically propeller conformation of TPE.Thus,the Calix-DPE(OCH3)4 is a AIEgen.Contrarily,owing to the strong intramolecular hydrogen bonding in the bottom rim,the Calix-DPE(OH)4 adopts a cone conformation which makes three phenyl rings of TPE almost perpendicular to the plane of the C=C bond that broken the cross-chromophore π-conjugation of TPE.Therefore,compound Calix-DPE(OH)4 lost the AIE property both in solution and crystal.The results prove that the maximal cross-chromophore π-conjugation within the tetraphenylethene is one of the prerequisites of switching on its AIE.Additionally,the unit cell of Calix-DPE(OCH3)4 comprises a pair of chiral enantiomers,which can be attributed to the introduction of a curvature in an ideal planar structure with a simple modification on the meso bridge of the calix[4]arene.The result enrichs the definition of ’inherently chiral’ and provides a new method to design chiral molecules.In the second part,a meso 1,1-diphenylmethylidene-decorated perethyl decorated pillar[5]arene(EtP5A-DPE)was designed and synthesized,in which the TPE unit was embedded in the pillar[5]arene skeleton in a way of sharing two aromatic rings.It is noteworthy that this is the first time to achieve the modification in the meso position of pillararenes.The single-crystal X-ray diffraction analysis revealed that the EtP5A-DPE adopted a torsion pillar conformation.The meso C = C bond position modification makes the pillar[5]arene(EtP5A-DPE)scaffold unsymmetrical and the two embedded phenyl rings adopt small dihedral angles(66.338(234)°,51.868(236)°)to the C = C bond,which endows this cage with the aggregation induced emission(AIE)properties.The further investigations are going on.