Design,Synthesis And Properties Of Mechanochromic Molecules Based On π-Conjugated Donor-Acceptor Structure

Under the stimulation of mechanical force,the fluorescence color or intensity of the mechanochromic material exhibits obvious changes,and has the regulation and diversity,which has broad application prospects in the field of optoelectronic materials.However,the current research on mechanochromic color change faces many challenges,not only need to consider the chemical structure and spatial conformation of the molecule itself,but also need to consider the intermolecular interaction and crystal state.Efficient solid-state luminescence is a prerequisite for the preparation of excellent mechanochromic materials.Aggregation-induced luminescent materials can overcome the aggregation-induced quenching phenomenon often seen in traditional organic fluorescent materials,thereby achieving efficient solid-state luminescence;similarly,the highly distorted molecular conformation can weaken the close face-to-face arrangement and interaction between molecules,thereby realizing intercrystalline state.of mutual transformation and efficient luminescence.Therefore,the synthesis of molecules with aggregation-induced luminescence properties and highly twisted configurations is an effective approach to obtain mechanoluminescent materials.This dissertation starts from the molecular structure and combines various donor and acceptor structures to construct π-conjugated molecules with highly twisted conformation and aggregation-induced luminescence properties,which provide an effective method for the directional design of mechanochromic materials.The results of research are as follows:The first part: The aggregation-induced luminescent molecules PBCAN and PBTAN were synthesized with carbazole or triphenylamine as electron donor and cyanoethylene as electron acceptor.PBCAN and PBTAN have opposite mechanochromic properties.The original crystal of PBCAN emits yellow fluorescence,which turns orange-yellow after grinding,and the fluorescence color of PBTAN shifts from yellow-blue to yellow-green after grinding.X-ray diffraction and solid-state absorption changes indicate that the switching of molecular packing states is the main reason for the opposite fluorescence shift of molecules.The second part:The aggregation-induced luminescent molecule TPEAN was synthesized with tetrastyrene unit as electron donor and cyanovinyl group as electron acceptor.Scanning electron microscopy experiments confirmed that the molecules aggregated in the THF/H2 O mixed solution with high water content,with obvious aggregation-induced luminescence properties.In addition,TPEAN also exhibits typical mechanochromic properties.After grinding the original crystal,the yellow-green fluorescence changes to orange-yellow,and it can return to the original state after fumigation.This process can be repeated many times.The study shows that the transition between a good crystalline state and a disordered amorphous state is the intrinsic cause of the red-shift of the force-induced fluorescence.The third part:Highly twisted phenothiazine ketone derivatives PTZ-BZ-Cz and PTZ-BZ-TPA with carbazole group or triphenylamine group as electron donor and carbonyl group as electron acceptor were synthesized.PTZ-BZ-Cz and PTZ-BZ-TPA have unique mechanochromic properties.PTZ-BZ-Cz were cultured in different solvents to obtain two kinds of crystals,showing the phenomenon of homogeneous polymorphism.One of the crystals emits green fluorescence(G-form),and after grinding,its fluorescence color is red-shifted to orange.The ground powder turns yellow after being fumigated by a solvent,and can be restored to green fluorescence after being heated or recrystallized to realize the three-color conversion of green,yellow and orange.Another crystal emits strong yellow fluorescence(Y-form),which can be reversibly converted from yellow to orange fluorescent states after grinding and fumigation.In addition,PTZ-BZ-TPA also exhibited red-shifted fluorescence properties after external stimulation.Powder X-ray diffraction and theoretical calculations indicate that the planarization of molecular conformation and the intramolecular charge transfer that produces the plane are the main reasons for the red shift of the fluorescence of the two compounds.