Design,Synthesis And Properties Of Mechanochromic Materials Of Carbazole Derivatives With Aggregation-induced Emission

Mechanochromic(MC)materials,is a kind of stimuli-response material,the photo-physical properties(such as absorption,fluorescent color,etc)can be switched reversibly upon external pressure or mechanical force.Because of this special properties,MC materials have important application prospect on pressure switch,force sensors,memory materials and anti-counterfeiting mark materials,and this material has received extensive attention of many researchers.Because of the strong molecular interactions,the traditional fluorescent molecules suffer from the aggregation caused quenching.This limits the development and application of MC materials.Recent years,the discoveries of aggregation-induced fluorescence emission(AIE)and aggregation-induced fluorescence emission enhanced(AIEE)materials have provided a new idea for the designing and synthesizing of MC materials.Organic small molecules luminescent materials with simple structures,are easy to be synthesized and modified,and its photo-physical properties are easy to be adjusted.Therefore,the organic small molecules with AIE(or AIEE)and MC properties and its synthesis and the practical application have important research value.In this paper,A series of novel AIE(or AIEE)-active carbazole organic small molecules with D-?-A structures were designed and synthesized,and the correlation between the molecular structure and MC behavior was studied and analyzed.1.The relationship between branched structure and MC propertiesThree branched compounds 5a-5c were designed and synthesized,which is based on intermolecular charge transfer.And the relationship between the molecular structure,the aggregation behavior and MC behaviors of these compounds were studied in detail.The results showed that 5a-5c have good aggregation induced luminescence performance.Due to the highly distorted molecular structure,5a shows high fluorescence emission(? 49.8%);The order molecular packing and good crystallinity induce that 5a displayed good MC behavior with an obvious red shift(598 nm to 643 nm)after grinding;The large molecular space steric hindrance induced the molecules of 5b and 5cdifficult to form crystal structure,which induced the molecules in amorphous state,and there are no obvious phase change before and after grinding,so 5b and 5c showed no MC properties.2.The relationship between different molecular packing of polymorphism and MC propertiesWe designed and synthesized a new AIE-active organic small molecule compound 6 by optimizing and designing the molecular structure,and we introduced fluorine atoms and cyano groups to the molecule,expected to form varied molecular packing modes.The results showed that powder 6 showed two different colors:yellow(6Y)and orange(60).The analysis of single crystal structure shows that the molecules have variable molecular packing modes and distorted molecular conformation,which leading to the different solid-state absorption and fluorescence emissions.The yellow solid powder 6Y is in a loose and lamellar-shaped arrangement.The loose molecular arrangement and weak molecular interactions caused 6Y with obvious MC behaviors.While the orange solid powder 60 is in a closely intersected arrangement,which cause 60 no MC behavior.In addition,upon heating,6Y can convert to 6O,and this change is not reversible.The theoretical calculation based on single crystal data confirmed that the single molecular energy 6Y is about 3.9 kJ/mol higher than that of 60,and 60 show a closely intersected arrangement mode,these caused that this fluorescence change of thermo-stimulus is non-reversible.3.The correlation between the different terminal groups,the intermolecular interactions and MC behaviors.A series of compounds C1-C4 and BC1-BC4 based on the carbazole-malonitrile were designed and synthesized by changing the terminal groups or the introduction of bromine atoms,which is looking forward to adjust the intramolecular electron distribution and weak intermolecular interactions.And the relationship between the molecular interactions,the molecular conformations and MC properties were studied.The theoretical calculation,the 1H NMR and single crystal structure analysis showed that through changing the terminal groups and bromine atom,the molecular electron cloud of these compounds had been changed or even reversal,the molecular conformations,intermolecular interactions and packing modes were also obviously changed.Due to the strong intermolecualr ?-? staking interaction,C1 and BC1 displayed aggregation-induced fluorescence quenching.The twisted molecular structure and the multiple intermolecular interactions induced the formation of J-aggregation,which caused the aggregation-induced fluorescence emission of C2-C4 and BC-BC4.The molecular arrangements of C1,C3,C4 and BC1,BC3 and BC4 are relatively loose,which induced them exhibit sensitive reversible MC behaviors;While the molecular arrangement of BC2 is relatively compact and order,which caused that BC2 is not sensitive to the mechanical force;Additionally,C2 displays non-reversible mechano-stimulus properties.The XRD analysis shows that mechano-stimulus properties are mainly attributed to the crystalline structure of the molecule easily to be destroyed by external forces.