Study And Application Of Stability And Structure Principle Of Organic Radical Luminescent Materials

Organic radical luminescent materials have received extensive attention recently.Their unique doublet emission properties can break through the limitation of spin transition prohibitions and theoretically reach 100% internal quantum efficiency,which has great application potential in the field of organic photoelectronics.However,radicals are highly active and unstable in nature,and stable and high-performance radicals are rare and the relationship between structure and properties of radicals is unclear.Based on this,this paper uses quantum chemistry to conduct in-depth and systematic research on luminescent radicals from the perspective of theoretical calculation,aiming at clarifying the relationship between the stability of radicals and their structural properties,and giving the basic design strategy of stable and high-performance radicals.The main research contents are as follows:(1)The inherent instability of radicals greatly restricts the development of luminescent radical molecules.Therefore,this paper constructs a systematic method to investigate the stability of radicals,including the thermodynamic stability,kinetic stability and electrochemical stability of radicals,as well as the influence of substituents on the stability of radicals.The relationship between the stability and structural characteristics of neutral donor luminescent radicals is revealed.The results show that small dihedral Angle and short bond length between radical acceptor and donor are beneficial to spin delocalization and improve thermodynamic stability.The large steric donor group can protect the central carbon radical in space and improve the kinetic stability.The weak donor and strong aromatic groups make the radical less prone to redox reaction and enhance the electrochemical stability.Based on the design strategies of these stable radicals,a radical stability index is proposed to evaluate the overall stability of radicals,and five high stability radical molecules are designed,which are potential high stability luminescent radicals worthy of further experimental study.This work provides important theoretical guidance for the development of highly stable radicals.(2)The electron arrangement of radical molecules usually follows the Aufbau principle,but the singly occupied molecular orbital(SOMO)of some radical molecules is lower in energy than the highest(doubly)occupied molecular orbital(HOMO),forming a uniquen non-Aufbau type structure.This kind of non-Aufbau luminescent radical molecule usually has high luminescent quantum yields and photostability.However,the design principle and method of non-Aufbau luminescent radical are not clear.Based on this,the geometric structure,formation mechanism,design strategy and exciton transition mode of non-Aufbau luminescent radical are studied systematically in this paper.It is found that the key to the formation of non-Aufbau radical molecules is the mutual repulsion between frontier molecular orbital.The exciton transition mode of non-Aufbau radical is the transition from β-HOMO to β-SUMO orbitals.This work has explored the mechanism of non-Aufbau luminescent radical and provided a simple design strategy for the development of non-Aufbau molecules.(3)At present,there are few kinds of luminescent radical materials,which are basically carbon center radical replaced by chlorine.New high performance organic radical luminescent materials are still to be explored.Based on this,a series of new radical molecules are designed by using heteroatomic substitution and electron-withdrawing groups for trichlorotriphenylmethyl radicals.The comprehensive stability,frontier molecular orbital,natural transition orbital,radiative decay rate,Root-mean-square deviation(RMSD)between ground state and excited state are calculated.The results show that it is feasible to construct new radicals by substituting bromide or adding electronwithdrawing groups,and the emission spectra shift blue with the increase of electron-withdrawing ability of substituents.The luminescence intensity is negatively correlated with RMSD.The RMSD value can be reduced by adjusting the dihedral Angle of electron-withdrawing groups to make the molecular geometry more stable and enhance the radiative decay rate.In addition,the newly designed adical has high stability and good luminescence performance,which has great potential for development and application.This work provides an idea for designing new efficient luminescent radical materials.