| Emission properties,including color,photoluminescence efficiency and lifetime,depend on excited-state characteristic and process.Therefore,it is significant to modulate light-emitting properties and develop high-efficiency light-emitting materials by studying excited-state properties.The intrinsic characteristic of excited state is exciton binding energy(or exciton delocalization radius),and it can be achieved by using intermolecular interaction(?-? and H-bond interactions,etc)to construct aggregates with different sizes.In order to reveal the intrinsic characteristic of supramolecular aggregates,we start from the simplest and smallest supramolecular aggregate model(dimer),and further study the relationship between discrete intermolecular ?-? stacking dimer structures and properties.Based on the above research ideas,on the one hand,we wish to design high-efficiency intermolecular ?-? stacking dimer materials and develop special functions and applications;on the other hand,gradually increase the size of aggregates and extend to supramolecular systems,establishing new concept of supramolecular excited state and enriching and perfecting the theoretical basis of supramolecular luminescence science.In this paper,combining experimental measurements and theoretical calculations,we designed and synthesized a series of ?-plane aromatic compounds with one-side substituent,systematically studied their stacking structures in crystal,and investigated their photophysical properties of single molecule and ?-? stacking dimer.We also revealed the essential characteristics of excited state for high-efficiency ?-? dimer,established the relationship between ?-? dimeric packing structures and luminescent properties,and provided theoretical guidance for realizing their special functions and applications.The main results in this paper are as follows:1.We found a high-efficiency anthracene ?-? dimer-G-phase crystal(77%)of m TPA-9AN,and its efficiency is much higher than that of the polymorphism-B-phase crystal(8.1%).High-efficiency anthracene ?-? dimeric luminescence can be explained: compressed ?-? dimeric geometry in excited state,intermolecular hybridized local and charge transfer(HLCT)excited state as the excited-state essence and discrete ?-? dimeric stacking,effectively suppressing the non-radiative transition process.Besides,we proposed a design strategy of high-efficiency discrete dimers: the target molecule should contain a ? plane which was substituted on one side,and the substituent must have the right size on one side of the ? plane.2.We surveyed the temperature dependence of ?-? dimeric luminescence: on the one hand,we found that B-phase crystal of m TPA-9AN could be transformed into Gphase crystal after heating,accompanied by synchronous changes of their photophysical properties,demonstrating the origin of high-efficiency dimeric fluorescence from discrete ?-? dimeric stacking;on the other hand,we observed an unusual blue shift in anthracene ?-? dimeric fluorescence with increasing temperature,originating from the significantly increased interplanar ?-? distance of the anthracene dimer in excited state with increasing temperature,and the anharmonic potential energy curve of dimer along ?-? interaction direction.3.We achieved red(orange-red)?-? dimeric emission using aromatic perylene as ?-moiety,and realized high-efficiency perylene ?-? dimeric emission(77%).The work verifies the molecular design strategy for constructing high-efficiency discrete ?-? dimeric stacking,further validates the HLCT state of ?-? dimer in excited state,and indicates that discrete degree is the main reason that affects luminescent efficiency of ?-? dimer.4.Guest molecules were inserted in the middle of ?-? dimer,extending the system from dimer to trimer,and the influence of the introduction of guest molecule on the luminescent properties of ?-? dimer was explored.By adjusting the energy level of frontier orbital in guest molecule,we realized the excited-state modulation of ?-? trimer,including full-color fluorescence of red,green and blue from cocrystal,and the rare thermally-activated delayed fluorescence(TADF)emission.For the cocrystal with intermolecular charge transfer(CT)interaction,compared with long-range mixed stacking cocrystal,the ?-? trimeric stacking complex has stronger interactions in excited state,resulting in larger red-shift emission. |
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