Aromatic Nitric Acid Radical

Since the Nobel Prize in Chemistry was awarded in 2000 for the discovery of conductive polymers,the research of organic semiconductors has become a hot and important field.For organic semiconductor molecules,the excited state has been extensively studied,and there is relatively little attention to the electronic ground state.Strictly speaking,the electronic ground states of organic semiconductors can be divided into two categories:closed-shell singlet and open-shell singlet/doublet/triplet states.Among them,closed-shell singlet organic semiconductors are relatively stable and most common,and have been successfully commercialized in the field of organic electroluminescence.The open-shell singlet,doublet and triplet ground state molecules usually contain free radicals and have poor stability,which greatly limits their practical application.This thesis will focus on oxygen radicals and carry out relevant research on stable open-shell radicals.In experiments,we unexpectedly discovered that a class of cheap and easily synthesized triphenolamine radicals had excellent electrochemical and thermal stability,so we further designed and synthesized a series of conjugated triphenolamine radical molecules.Such molecules have extremely strong electron paramagnetic resonance signals,and their absorption spectrum covers the entire ultraviolet to near infrared region.More interestingly,these conjugated nitroxide radicals can be regarded as aromatic nitro or nitric acid radicals,and their rich closed-shell nitro-like and open-shell singlet/triplet ground state resonance structures contribute to excellent thermal stability and electrochemical stability.Therefore,we propose"aromatic nitric acid radicals"to perfectly explain the source of stability.Meanwhile,we found that molecules are prone to be protonated in the solution state,but easily oxidized and form a quinone radical conformation in the aggregated state.The aggregation effect effectively stabilizes radicals,so an"aggregation-induced radical"effect is proposed to explain the transformation from closed-shell to open-shell singlet resonance structure.Further,we believe that this design strategy can be extended to inorganic acids such as H₂CO₃,H₂SO₄ and H₃PO₄,and can be extended to the concept of"aromatic inorganic acid radical"for the design of various stable organic radical semiconductor materials.In order to increase the solubility and film-forming properties of the material,we have also prepared star-shaped aromatic nitric acid radicals with larger molecular weights.Star-shaped aromatic nitric acid radicals with planar conjugated and non-planar central cores both exhibit good electrochemical stability,while molecules with non-planar central cores exhibit stronger near-infrared absorption and electrons paramagnetic resonance intensity.This is because the conjugated molecules with planar central cores produce better electron delocalization,which makes the intramolecular spin interaction stronger.The spin concentration of the planar conjugated radical material would decrease under stronger antiferromagnetic coupling.Compared with its methoxy precursor,the star-shaped radical material with a non-planar central core has nearly three orders of magnitude improvement in electrical conductivity,reaching a maximum of 3.83×10^-2 S m^-1.In addition,TPA-TPA-O₆ with high conductivity is used as a hole-transporting material in organic solar cells.The results show that the material has a general hole-transporting ability.This paper provides a universal strategy for designing and synthesizing radical molecules with high spin concentration.Unlike closed-shell molecules and open-shell radical systems that have been widely studied in the past,our materials exhibit excellent electrochemical and thermal stability,higher charge mobility,solubility in polar low-toxic solvents such as alcohols/dimethyl sulfoxide.These materials have unique and regulated ground state electronic properties,and thus have potential application potential in many fields such as electronics,magnetism,spintronics,optics,and biology,and provide new ideas for the design of organic semiconductor materials.