Theoretical Study On The Effect Of Solvation On Charge Transfer States In Donor-acceptor Luminescence Molecules

Electroluminescence refers to the phenomenon in which electrons and holes are injected into a luminescent material when it is energized and then transported and recombined to emit light.It is a light-emitting process that can convert electrical energy into light energy.Organic electroluminescent materials have many advantages such as low cost,simple processing,fast molding,high brightness,fast response speed,and flexible processing.It has been gradually commercialized in recent years,but there are still some problems in the luminous efficiency,luminescent performance and material life of luminescent materials.In practical work,the molecules are mainly in the aggregated state whether in solution or in the device,so the environment where the molecules are located has a great relationship with the luminescent state.In order to accurately describe the actual working state of the molecule,this paper will take the molecular solution and aggregation state as the main research objects,and analyze the luminescence properties of the molecule in the solvent and in the aggregation state,to auxiliary experiments,explain some luminescent phenomena,and further design better luminescent molecules.In this paper,a series of theoretical studies on molecular excited states in solvents of different polarities are carried out using quantum computing methods combined with PCM models,and the effects of solvents on molecular configuration and excited states are analyzed,and then inferred the influence of the environment on its luminous performance,by calculating the recombination energy,the energy relaxation and system energy changes of the molecules in the solvent and aggregation states are judged,and the changes in the luminescence properties of the molecules in different environments are verified.First,in order to verify the effect of different polar solvents on the excited states of luminescent molecules,we selected three molecules with different excited state transition properties for research,namely TPA-AN,which is dominated by LE state transition,and TPA-NZP,which is dominated by HLCT state transition,and CT state transition dominated PXT-TRZ.We selected solvents of different polarities for verification,low-polarity n-hexane,medium-polarity tetrahydrofuran and high-polarity acetonitrile,computational simulations of the ground state,excited state configurations,transition properties and luminescence properties of molecules in solvents of different polarities.It has been verified that molecules with a larger proportion of CT state are more sensitive to solvent polarity,that is,the greater the polarity,the more obvious the change of CT state molecules.Its luminescent properties can also be seen that as the polarity of the solvent increases,the degree of encapsulation of the solvent is enhanced,and the vibration of the molecule,especially the in-plane vibration,is suppressed,but the vibration of the luminescent center is enhanced with the increase of polarity,which also explains When the solvation effect occurs,the luminous efficiency of the molecule decreases and the spectral fine structure disappears.Furthermore,in order to further verify the effect of environment on the properties of luminescent molecules with different properties,we chose PBTPA,a molecule with both AIE and HLCT state properties,to find out the AIE-HLCT mechanism of environment aggregation.Simulations of the molecule in different solvents show that in the ground state configuration,the angle of the molecule increases with the increase of the solvent polarity,while in the excited state configuration,as the solvent polarity increases,part of the angle decreases,and the other part decreases instead increase,We compared the molecular configurations and found that with increasing solvent polarity,the RMSD value decreased.This validates the solvation effect due to the stronger encapsulation of the polar solvent.In order to further determine which part of the molecule affects the luminous efficiency,we calculated the recombination energy of the molecule.First of all,the molecule has the properties of HLCT state and AIE at the same time,We simultaneously found in different polar solvents and aggregated states that the excited state energy of the molecule produces a smaller energy difference and larger orbital coupling with the aggregation of the molecule,which facilitates further reverse intersystem crossings,At the same time,the configuration change of the molecules in the aggregation state is suppressed,and the vibration is greatly reduced,which reduces the non-radiative energy loss of the molecules and is beneficial to the luminescence of the molecules when they are aggregated.This part explains the luminescence mechanism of the molecular HLCT-AIE and lays a foundation for the further design and synthesis of such molecules.