Design,Synthesis And Piezochromic Properties Of Cyano Isomeric Derivatives

Piezochromic materials as a common type of stimulus-response functional material,can change its luminescent performance under external force stimulation such as grinding,shear or compressive force.Compared with other kinds of piezochromic materials,organic piezochromic materials show great application prospects in the fields of photoelectric display,pressure sensor,optical storage and anti-counterfeiting because of their advantages of easy regulation of light color,easy mass synthesis,low price and reusable et al.The essence of the piezochromic effect is that external force induces the changes of molecular aggregated structure or molecular conformation,which cause the disturbance of electronic energy levels,the phase changes,the appearance of lattice defects or the isomerization of molecular structure,and finally make effects on the band shape and position of electron absorption and the emission spectra of luminescent materials.Isomers usually have the same functional groups and different molecular stacking patterns,which can produce different stacking patterns under different external stimuli.They are an ideal system for analyzing stimulus response performance.At present,there is still a lack of systematic research on the barochromic properties of isomers under isotropic hydrostatic pressure.In this thesis,we constructed a series of cis/trans isomers and positional isomers containing cyano groups with aggregation induced luminescence properties,studied the relationship between isomer molecular structure,crystal stacking mode and piezochromic properties,and obtained piezochromic materials with high sensitivity.The main research contents of this paper are as follows:(1)Trans(E)-2,3-di(naphthalene-2-yl)acrylonitrile(E-CCN),cis(Z)-2,3-di(naphthalene-2-yl)acrylonitrile(Z-CCN)and(anthracene-9-yl)-2-(naphthalene-2-yl)acrylonitrile(ANCN)are synthesized,they use modifying anthracene and naphthalene at both ends of the double bond of monocyano olefin molecule by Mc Murry reaction.When the crystals of the above three molecules are processe by mechanical force grinding,the ordered stacking structure of the crystals is destroyed and transformed into amorphous form.The fluorescence emission peak of E-CCN crystal shows 24 nm blue-shift,and the fluorescence emission peak of ANCN crystal shows 25 nm red-shift,while the fluorescence color of Z-CCN crystal almost have no piezochromic phenomena.Powder X-ray diffraction(PXRD)experiment show that different piezochromism phenomena are due to the orderly molecular stacking arrangement and intermolecular interaction in the crystal,which is easy to be destroyed,resulting in the orderly stacking of the crystal into amorphous state.It is speculated that the different changes of fluorescence may be due to the interruption of the conjugation between adjacent molecules in E-CCN crystal by mechanical grinding,resulting in the blue-shift of fluorescence spectrum,the enhancement of intermolecular conjugation degree in ANCN crystal,resulting in the red-shift of fluorescence spectrum.Under hydrostatic pressure,the fluorescence spectra of the three crystals showed a wide range of red-shift(103 nm,121 nm,183 nm).The pressure range of E-CCN and ANCN crystals under hydrostatic pressure shows a good linear relationship with the change of fluorescence peak position,it is calculated that the sensitivity of E-CCN and ANCN crystals under hydrostatic pressure is 7.31 nm·GPa^-1and 21.45 nm·GPa^-1respectively.The red-shift range of the fluorescence peak of ANCN crystal is also much larger than that of E-CCN crystal(183 nm>103 nm),indicating that ANCN crystal has better sensitivity and greater light color contrast.(2)Cis/trans isomer molecules E-ANTCN and Z-ANTCN are designed and synthesized with p-cyano olefin as the central core and 9-anthracene groups connected on both sides of the double bond.C-H…?interaction and intermolecular charge transfer(ICT)exist in Z-ANTCN crystal,resulting in the fluorescence emission peak the blue-shift of 17 nm and the red-shift of 110 nm under mechanical grinding and hydrostatic pressure,respectively.In the hydrostatic pressure experiment,E-ANTCN crystal does not show obvious piezochromic properties,but in a certain pressure range(3.15 GPA-7.17 GPA),a new fluorescence peak appears in the fluorescence spectrum at 700 nm.This phenomenon may be due to the intermolecular?-?interaction and the formation of excimer association under hydrostatic pressure.This chapter studies the piezochromic properties of cis/trans isomeric crystals under different forces,analyzes the relationship between molecular structure crystal stacking piezochromic properties,and reasonably explains the different piezochromic phenomena caused by different crystal stacking structures and intermolecular interactions.This work provides an idea for the construction of high sensitivity piezochromic materials.(3)Two anthracene-based structural isomers,NDHA-p and NDHA-m,are developed applying 9,10-bis(diphenylmethylene)-9,10-dihydroanthracene(DHA)as the basic skeleton and substituted by four cyano groups on para-or meta-position of the periphery benzene rings,respectively.The piezochromic properties of two molecular crystals are studied,and the relationship between the stacking mode of positional isomers and piezochromic properties is explored.Both NDHA-p and NDHA-m have aggregation induced luminescence properties and similar to highly distorted molecular conformations,but the stacking modes of crystals are different:there are abundant intermolecular interactions in both molecular crystal structures,while there are 8 types of C-H…N hydrogen bonds in NDHA-p crystals,and only 2types of C-H…N hydrogen bonds are observed in NDHA-m crystals.NDHA-p crystal is ground by mechanical force,and the fluorescence emission peak shifted from 520nm to 480 nm.Combined with powder X-ray diffraction(PXRD)experiment,it showed that mechanical force grinding destroyed the intermolecular interaction,the conjugation between adjacent molecules was interrupted,and the regularly arranged molecules became amorphous,resulting in blue-shift emission.After fume or annealing,the ground powder returned to the initial luminescence state,indicating that solvent fume and annealing reconstructed the intermolecular interaction.NDHA-m crystal has almost no piezochromic properties under the mechanical force grinding.In high-pressure experiment,as compared to the NDHA-m which shows a color contrast of 60 nm and a sensitivity of 7.87 nm·GPa^-1,NDHA-p exhibits a dramatically larger color contrast of 138 nm and higher sensitivity of 13.20 nm·GPa^-1.The molecular structure of positional isomers will have an important impact on the stacking mode of crystals,resulting in the difference between mechanical grinding and piezochromism under hydrostatic pressure.This work provides a useful reference for improving the piezochromic properties through the isomerization of substituents.