Regulation Of Excited State And Thin-Film Application Of Pyrene Dimer

Organic aggregated light-emitting materials are characterized by diverse luminescent properties and have found a wide range of applications in organic optoelectronic devices,displays,lighting,anti-counterfeiting,data encryption,stimulus response,and fluorescent probes.As a source of innovation,the excited states of organic light-emitting materials deserve rational design and precise regulation.While the excited state properties of single molecules are well studied and understood,those of aggregates,which are heavily affected by supramolecular interactions,are much more difficult to study.Intermolecular dimers,as the simplest supramolecular aggregates,are not only links connecting single molecules and aggregates,but also ideal models for studying the excited state properties of aggregates.Pyrene was the first molecule to exhibit dimer emission,and its fluorescence properties have been thoroughly studied.However,there are still issues that need to be addressed urgently.First,due to the complexity of the excited states of pyrene dimers,which always exhibit variable fluorescence properties,it is still unclear how to precisely control their excited state structure for specific luminescence properties.Second,intermolecular forces significantly affect the stacking patterns of pyrene derivatives,but a clear molecular design strategy for the construction of stable single pyrene dimers is still lacking.Finally,pyrene dimers are currently generally formed in crystals or concentrated solutions,which limits the exploitation of their unique properties and functions.Based on the above problems,this paper conducts in-depth research on the structure-performance relationship of pyrene dimers by combining experimental and theoretical methods from the perspective of regulation of intermolecular interaction forces(such as π–π interactions,hydrogen bonds,etc.).so as to provide guidance for understanding the excited state characteristics of aggregates.Firstly,polymorphic pyrene aggregates and pyrene dimers were constructed by regulating the intermolecularπ–π interaction and substituent structures.The properties of the excited-state structure of pyrene dimers have been explored by means of a two-dimensional potential energy surface in order to understand the effect factor of the excited states of the aggregates.Secondly,the precise construction and film preparation of single strong π–π pyrene dimer were realized by enhancing the π–π interaction for the purpose of providing an ideal aggregate model and proposing a molecular design strategy for designing strongπ–π discrete dimers.Finally,multiple non-covalent interactions were introduced to enable reversible assembly of different aggregates through the competition between pyrene monomer and pyrene dimer excited states.Characteristic applications of pyrene dimers in time-dependent optical recording and data encryption in thin film states have been explored.The specific research is as follows:We constructed the discrete pyrene dimer stackings and simulated the twodimensional potential energy surface of the pyrene dimer to understand the nature of its excited states.By regulating the intensity of π–π interaction and optimizing the substituent structures,polymorphic pyrene aggregates and pyrene dimers were constructed,which showed different fluorescence color and fluorescence lifetime.The discovery of multiple potential wells in the ground-and excited-state two-dimensional potential energy surfaces of pyrene dimers by theoretical simulations illustrates the essential reason for the diversity of their luminescence properties.And the pyrene dimers with a single packing were constructed by evaporation and their application potential for use in electroluminescent devices was explored.We proposed an electron delocalization strategy to enhance the intermolecular π–π interaction and construct pyrene dimer stacking with strong π–π interaction.The electron density of the pyrene group was dispersed by the double bonds to reduce the electrostatic repulsion between the two pyrene groups,and the long-range aggregation tendency of the pyrene groups was blocked by the side groups.Thus,a single discrete strong π–π pyrene dimer was precisely constructed in crystals and films.Then,the inhibitory effect of intramolecular π conjugation on intermolecular π–π interaction was explored and the electron delocalization strategy for constructing discrete strong π–πdimers was proposed and improved.Finally,the application potential of strong π–πpyrene dimer films in acidichromism sensors and electroluminescent devices was studied.We proposed a competitive strategy based on non-covalent interactions to achieve the transitions between monomer and dimer excited states in pyrene dimers.The pyrene group was modified by substituent groups with hydrogen bonding sites,and a pyrene dimer with hydrogen bonds and π–π interactions,which are comparable in strength,was constructed.The competition of hydrogen bonds and π–π interactions induced the change in fluorescence properties of different aggregates,characterring as blue fluorescence in the crystalline state and yellow fluorescence in molten state,which were dominated by monomer excited state emission and dimer excited state emission,respectively.Moreover,molten films were prepared for laser-induced reversible optical recording and novel time-dependent data encryption.