The Design,Syntheses And Properties Study Of Stimulus-Responsive Compounds Based On Planar Structures

Photochemistry is a branch of chemistry concerned with the configuration and physicochemical properties of excited state of molecules.Materials that can change emission color or intensity upon external stimuli in the solid state will provide solutions for increasingly sophisticated application needs.Purely organic stimuli-responsive compounds have attracted much attention due to their low toxicity,low cost,and ease of modification.Thus,it is of great importance to study the photochemical properties of purely organic luminogens.The photochemical properties of organic compounds in solid state are not only related to their own structures,but also closely related to their solid-state packing modes,especially the crystal packing modes.It is of great significance to study the relationship between the structure and molecular packing of organic molecules and their luminescent properties.By chemical structures modification and intermolecular interactions regulation,purely organic luminogens with stimuli-responsive behaviors were synthesized in this thesis based on the compounds with rigid planes.We tried to find the connection between the emission wavelength,the decay process of excitons and the molecular configuration and distances between molecules.All of these compounds exhibit one or more specific luminescent properties,including mechanoluminescence,room temperature phosphorescence,mechanochromism and response to photo-stimulus.The main contents are as follows:Chapter one: Firstly,a brief introduction of research contents of photochemistry was presented.Then the stimuli-responsive behaviors of mechanoluminescence materials,room temperature phosphorescence materials and photo-stimulated emission responsive materials were reviewed in detail.At last,we put forward the design ideas and contents of this thesis.Chapter two: Based on the bromine-substituted fluorene derivatives,the effects of Br···Br interactions on the mechanophosphorescence and photophosphorescence properties of the materials were investigated.It is found that the strong Br···Br interactions can play a pivotal role like the external heavy atom effect,which is accountable for the high phosphorescence efficiency of dual-emissive Br Flu-CBr.By destroying the Br···Br interactions,the phosphorescence emission intensity could be reduced and the emission color of photoluminescence and mechanoluminescence could be tuned.Chapter three: In this chapter,fluorene was replaced by dibenzofuran,and Cl AcDBF with ultra room temperature phosphorescence property was synthesized based on Cl···Cl interactions.At the same time,it also has dual phosphorescent emission properties with different lifetimes.Cl Pi-DBF without Cl···Cl interactions in crystals exhibits longer phosphorescence lifetime but much lower phosphorescence efficiency.The results demonstrate that the Cl···Cl interactions also play a role like the external heavy atom effect,enhancing the phosphorescence efficiency and reducing the phosphorescence lifetime,which provide a new idea for us to synthesize molecules with dual phosphorescent emission property.Chapter four: Based on the hydrogen bonding,a compound Xan-EPTf with the highest photoluminescence quantum yields compared to the comparative compounds Xan-EPBr and Xan-E2 PBr in solution,crystal state and film state was synthesized.Similar to the photoluminescence process,crystals of Xan-EPTf also have bright mechanoluminescence upon mechanical stimulus.Spectroscopic study results show that the mechanoluminescence process and the photoluminescence process produce similar excited states.The analyses of single crystal and theoretical calculations demonstrate the important role of the trifluoromethyl group in forming hydrogen bonds,which can effectively suppress the non-radiative transition process of excitons.Chapter five: Using xanthene as a template compound,we introduced pyrene units to the 4-and 5-position of it to form intramolecular excimers.which help to realize the precise regulation of ?-? interactions between the pyrene units,thereby controlling the fluorescence emissions and the triplet-triplet annihilation processes.The single crystal analysis results show that the longer the distance between the units,the more blue-shifted the emission wavelength of the excimer and the faster the quenching rate of the triplet.Therefore,the crystals of X2 P and the needle crystals of X2 EP with more pyrene units and larger conjugated structures have a more blue-shifted luminescence than the X1 P crystals.By regulating the tightness of the crystal packing,we can tune the mechanical-stimuli-responsive properties of the materials.It is also possible to predict the distances between the ? units by the emission wavelength of the excimer.Chapter six: By replacing the two benzene rings of tetraphenylethylene with anthracene derivatives,a water-soluble compound DPEDA-4NBr with significant photo-induced luminescence-enhancing property was designed and synthesized.In the nano-aggregated state,it has a photo-induced aggregation-induced emission effect.After photo irradiation,the fluorescence quantum yield in the solid state could be increased by 289 times with high contrast.Based on powder X-Ray diffraction patterns,infrared absorption spectra and theoretical calculations,we found that under UV irradiation the compound underwent the transformation between the anthracenestructure and the quinone-structure.The strong ICT effect in the anthracene-structure leads to the quenching of emissions,while the weakening of the ICT effect in the quinone-structure gives the compound a strong fluorescence.Due to the high-contrast fluorescence emissions of DPEDA-4NBr before and after UV irradiation in the solid state,we applied it to the light-painting patterns and painted a series of different patterns with UV light.At the same time,these patterns can be easily and environmentally friendly erased through water vapor or ethanol vapor,providing the possible applications in the field of information encryption.