Investigating The Influence Of Substituent Groups In TTM Based Radicals To The Fluorescent Illuminating Process: A Theoretical Study

Tri-（2,4,6-trichlorophenyl）methyl（TTM）based radicals can be promising in providing relatively high fluorescent quantum efficiency（φ_f）.In this study,we have evaluated the properties of a series of radicals with substituent groups introduced into TTM by means of comprehensive computational approaches.The optimal configurations of the fluorescent associated ground states（D₀）and first excited states（D₁）for each radical are calculated and the computed emission spectra are comparable with previous experimental reports.Furthermore,the influences to the radiative decay process（k_r）and the non-radiative decay process(k_nr)from the substituent groups are also elaborately addressed.The influence of the substituent groups to k_ris attributed to the transition dipole moments（p）and the energy gaps between D₀and D₁（ΔE）.The k_nris primarily determined by the non-adiabatic coupling matrix elements（NACME）,ΔE and the reorganization energies from low-frequency vibrations(λ_lf).According to our calculation,the introduced conjugated structures from the substituent groups are the reason for the higher k_rand the corresponding lower k_nr.Besides,two fluorine substituted radicals,namely 2F-TTM-PCz and 4F-TTM-PCz have been designed.Comparing to chlorine atoms,the fluorine atoms are able to increaseΔE of2F-TTM-PCz and a higherφ_fhas been predicted.However,φ_fof 4F-TTM-PCz is much smaller since its k_nrhas been greatly increased due to the considerable increase ofλ_lf.We expect our calculation can benefit the design of light-emitting molecules in further experiments.This paper is divided into four chapters.The first chapter is the introduction.It mainly introduces the types of stable radicals,the application of radicals in organic light-emitting diodes（OLEDs）,and the stable light-emitting radical TTM.In addition,it also introduces the topic selection and main content of this paper.The second chapter is the theoretical basis,covering the basic knowledge of quantum mechanics,quantum chemical calculation methods and discussion on the selection of basis group.Because this paper involves the radiation and non-radiation transition process of electrons,the basic formulas and principles used in theoretical evaluation of the two transition processes are also briefly described in this chapter.The third chapter is a series of theoretical evaluation of the luminescence principle of different free radical luminescent molecules.After the correct calculation and analysis of the synthesized molecules,the theoretical study of self-designed molecules is also carried out.The main research highlights are as follows:1.The influence of the substituent groups to the orbitals of open-shell radicals associated with D₁to D₀electronic transitions have been considered with Natural Transition Orbital（NTO）analysis.The effects to the charge transfer during emission processes have been identified.2.The influence of the substituent groups to k_ris ascribed to the transition dipole moment and the energy gap between D₀and D₁,which are both in association with the conjugated structures in the substituent groups.3.The k_nris primarily determined by the non-adiabatic coupling matrix elements（NACME）,the energy gap between D₀and D₁and the contribution of vibronic coupling in the low-frequency region(λ_lf).λ_lfcan be decreased by linking TTM with a substituent group containing a relatively large conjugated structure.4.Two fluorine substituted radicals,namely 2F-TTM-PCz and 4F-TTM-PCz have been designed.The energy gaps between D₀and D₁are both increased and a higherφ_fhas been predicted for 2F-TTM-PCz.It provides ideas for the future experiments involving free radical luminescent molecules.The fourth chapter is the summary and prospect of this paper.