Properties Of Stable Luminescent Carbon Radicals Modified With Deuterated Carbazole

Normally,organic radicals are highly reactive and unstable,which are often used as reactive intermediates in chemical reactions.However,in 1900,researchers discovered the first example of a relatively stable neutral organic radical,the triphenylmethyl radical.Subsequently more and more stable organic radicals were reported.Organic radicals with unpaired electrons exhibit unique optical,electrical,and magnetic properties.Through doublet emission,the theoretical upper limit of the internal quantum efficiency for radical-based devices can reach 100% under the condition of electric excitation.At present,the stable luminescent radicals are mainly concentrated in biphenylmethyl and triphenylmethyl radicals.In recent years,researchers have mainly introduced donors into the radicals,which improved the stability and luminescence efficiency of the radicals.Unlike previous studies,this thesis starts with kinetic isotope effects(KIE).Compared with hydrogen(H),deuterium(D)has a smaller van der Waals radius and the C-D bond has smaller vibrations and torsions,which is beneficial to reduce the non-radiative transition rates and improve the luminescence efficiency of the material.Moreover,the bond length of C-D bond is smaller,and the bond energy is larger,which is beneficial to improve the stability of the luminescent material.Therefore,this thesis investigates the effect of deuterium modification on the properties of luminescent radicals by introducing C-D bonds to N-substituted groups.First,the biphenylmethyl radicals were modified with deuterated carbazole to obtain two stable Cz BTM derivatives,BTM-1DC z and BTM-2DC z.The thermal stability as well as the photostability of the radicals modified with deuterated carbazole was further improved according to the results of stability measurements.Especially,the thermal decomposition temperature of BTM-1DC z was increased by 20 °C.From the photophysical property characterization,we found that the introduction of C-D bond could reduce the non-radiative transition rates and improved the luminescence efficiency of the radical derivatives.However,the non-radiative transition rates of the biphenylmethyl radical C z BTM are much larger than the radiative transition rates,which leads to a very limited improvement of the luminescence efficiency through the introduction of C-D bonds.Secondly,triphenylmethyl radicals were modified-with deuterated carbazole to investigate the effect on the properties of the triphenylmethyl radical.Two triphenylmethyl radical derivatives,TTM-1DCz and TTM-2DC z,were obtained by introducing deuterated carbazole groups,which exhibited high stability and high luminescence efficiency.TTM-1DCz and TTM-2DCz showed excellent thermal stability and photostability.The fluorescence quantum efficiency of TTM-1DCz and TTM-2DC z was improved to different degrees.In particular,the PLQ E of TTM-1DCz was improved by 25% compared with that of TTM-1Cz without deuterated modification.This is attributed to the smaller vibrations of the C-D bond,which reduces the non-radiative transition rates and facilitates the fluorescence generation.The radiative transition rates of the triphenylmethyl radical itself are closed to its nonradiative transition rates,thus,reducing the non-radiative transition rates can effectively improve the luminescence efficiency.Therefore,the modification of deuterated carbazole group is more effective in enhancing the luminescence efficiency of triphenylmethyl radical.The above work demonstrates that the introduction of C-D bonds can significantly reduce the non-radiative transition rates and lower the energy of the molecular system,results in improved stability and luminescence efficiency.This work provides a reference for the following development of high-performance light-emitting radical materials and devices.