Design,synthesis And Studies On Regulating The Conformations Of Tetraphenylethene Derivatives

Tetraphenylethene(TPE)derivatives have been attracting increasing research interests and applications in the past decade because of their intriguing aggregation-induced emission(AIE)properties,sample structure and easy modification.The degree of the cross-chromophore π-conjugation,determined actually by the dihedral angles between the phenyl moieties and the C=C bond in the TPE compounds,was revealed to play an important role in determining their AIE emission properties,which propose a new method to regulate the AIE properties by control their conformations.Fine tuning over the emission property of TPE derivatives has been successfully realized by tuning the molecular conformation using crystal engineering method.However,extensive investigations have revealed that it is too hard to regulate the AIE properties of TPE compounds in relatively wide range since it is very much difficult to control the TPE molecule to employ the conformation with non-or weak emissive nature by means of crystal engineering technique.In the present work,the alkoxyl chains with different length are employed to link the ortho position of the two phenyl moieties on one end of ethylene in the TPE frameworks,resulting in a successful regulation over the molecular conformationIn the first part,We introduced alkoxyl chains with different length ranging from one to four carbons are employed to link the ortho position and synthesized series of novel TPE compounds:TPEC1,TPEC2,TPEC3,TPEC4和 TPEOMe.This in turn induces different emission properties for this series of novel TPE compounds.In crystal state,two cis phenyl groups of TPEC1 adopt an almost perpendicular conformation to the C=C bond,rendering this compound a very weak emissive nature.In solution,TPEC1 is an ACQ luminogen for its similar structure with triphenylethene.In good contrast,the two phenyl moieties at the same ethylene carbon of TPE of TPEC3 are almost perpendicular to the C=C bond,resulting in a weak AIE luminogen nature and mechano-emission property to this compound.Intramolecular rotation and vibration of the TPE molecules with typical propeller conformation for both TPEC2 and TPEC4 as well as the unlocked reference compound TPEOMe have been efficiently suppressed in solid state,rendering these compounds typical AIE nature with the emission property changing depending on the dihedral angles between the four phenyl moieties and the C=C bond.The results confirms that the maximal cross-chromophore π-conjugation within the tetraphenylethene framework is a necessary prerequisite for their AIE emissionIn the second part.TPEC4 exhibited typical temperature dependence and concentration dependence in solution.These crystals with the same conformation structure and different packing modes which resulted in the temperature and concentration dependence,were achieved through solvent evaporation of TPEC4 in two mixed solvents.