Design,Synthesis And Performance Of Purely Organic Delayed Fluorescent And Room Temperature Phosphorescent Materials

Stimuli-responsive luminescent material refers to a type of functional luminescent material showing reversible optical behaviors such as absorption,fluorescence,phosphorescence change,etc.under the stimulation of light,electricity,force,heat,pH,etc.This kind of material has wide application prospects because it can be used in the fields of bio-imaging,sensors,information storage,anti-counterfeiting,organic light-emitting diode,etc.So far,fluorescent materials with stimuli-responsiveness have made significant progress,but delayed fluorescent and phosphorescent materials with stimuli-responsiveness are still very rare.In this dissertation,benzophenone is used as the electron acceptor.By introducing electron donors with different conformations to adjust the intermolecular interaction,charge transfer and luminescent behavior,delayed fluorescence and room-temperature phosphorescence that are responsive to light or force are obtained.In the second chapter of the thesis,we designed and synthesized D-A-D' type small molecule ODFRPTZ without heavy atoms using benzophenone as electron acceptor and phenothiazine and dibenzofuran as electron donor.The benzophenone molecule alone does not possess the property of aggregation-induced emission(AIE).When a highly twisted phenothiazine unit is introduced as an electron donor,it exhibits AIE properties.ODFRPTZ crystal powder has a mechanochromic effect,and the luminescence can be converted from initial phosphorescence to delayed fluorescence under the action of external force.The ODFRPTZ crystal powder in the initial state changed into a disordered state upon external force,and with the fluorescence color changing from green to yellow,a large bathochromic-shift of 40 nm occurred.The crystalline powder has a phosphorescence lifetime of 0.4 ms at room temperature,and the lifetime is converted to 0.9 ?s after heavy grinding.This is because the molecular configuration of phenothiazine changes from quasi-axial to quasi-equatorial under the action of external force,which is more conducive to the generation of delayed fluorescence.In the third chapter,we tried to achieve persistent room temperature phosphorescence by introducing different electron-donating subunits.Considering that the highly twisted structure of phenothiazine may cause gaps between molecules,which is not conducive to the stability of triplet excitons,we replaced phenothiazine with a planar structure carbazole.The ODBTCZ synthesized in this chapter also has a D-A-D' type electronic conformation,which exhibits typical intramolecular charge transfer properties in solvents with different polarity.As the molecular polarity increases,the maximum emission peak gradually redshifts.The crystals of ODBTCZ manifest multiple emissions of prompt fluorescence,delayed fluorescence and persistent room temperature phosphorescence,which is quite rarely reported in pure organic molecules.The pristine crystal powder showed purple fluorescence and obvious room temperature phosphorescence with a long lifetime(?>400 ms)after removing the UV light.In addition,the initial crystalline powder was transformed from a crystalline phase to the amorphous state upon external force,and its fluorescent color was changed from purple to deep blue.In the fourth chapter,different electron donors were introduced on both sides of benzophenone.When carbazole and dibenzofuran are utilized as electron donors,the obtained molecule ODFRCZ not only has perisistent phosphorescence in the crystalline state,it also has the properties of mechanochromism and photochromism.The purple crystal gradually turned reddish with a new emission peak at 609 nm on the emission spectrum.Comparing the single crystals of ODFRCZ before and after UV illumination,it was found that the intermolecular interaction was changed,and unstable triplet excitons were generated during this process.Compared with ODBTCZ,the intermolecular interaction in ODFRCZ crystal is weaker,and this less restricted environment is more conducive to the photo-activated movement of ODFRCZ.After heavy grinding,the phosphorescence and photochromic properties disappear,and the fluorescence emission redshifts.