Phenothiazines(PTZs),have received a lot of attention for many optoelectronic applications,such as hole-transporting layers,functioning as host materials for organic light-emitting diodes;dye sensitizers in dye-sensitized solar cells;and hole-transporting materials for perovskite solar cells.However,studies on benzophenothiazine materials are limited.In this study,we synthesize three isomeric bis-benzophenothiazine compounds(D-PTZa,D-PTZb,and D-PTZc),all bearing an aromatic ring at the 1,2-,2,3-,and 3,4-positions,respectively.Next,we systematically investigate the relationship between their structures and properties and compare them with bis-phenothiazine compounds(D-PTZ).The highest occupied molecular orbital(HOMO)distributions for D-PTZb and D-PTZc are dispersed over benzophenothiazine moities,whereas the lowest unoccupied molecular orbitals(LUMOs)are localized at the middle phenyl-and naphthyl-groups,which are similar frontier orbital distribuitions to the D-PTZ case.For D-PTZa,the steric hindrance between the phenyl groups at the 1,2-and middle positions increases,significantly distorting its spatial structure.Therefore,its HOMO and LUMO distributions differ from those of D-PTZb and D-PTZc.Notably,the HOMOs in D-PTZa are dispersed over the middle phenyl group and nitrogen atom,whereas the LUMOs are localized at the naphthyl group.The hole/electron excitation and frontier orbital analyses demonstrate that strong local π → π* transition mixing with weak charge transfer transition is responsible for the luminescence of D-PTZb and D-PTZc.Interestingly,the ultraviolet-visible absorption spectra of all samples exhibit strong π → π* transition absorption and weak n → π* transition absorption.Furthermore,the conjugated length of the molecule can be effectively increased with the introduction of an aromatic ring,resulting in a red-shift in the maximum absorption wavelength.Compared to D-PTZ,D-PTZa emits yellow-green light with a photoluminescence quantum efficiency(PLQE)of 14%.In addition,the introduction of a phenyl group at the 2,3-position effectively stabilizes the HOMO energy level,slightly increasing its π → π* transition gap,while also emitting blue light with a PLQE of 1.7%.For D-PTZc,the introduction of a phenyl group at the 3,4-position better linearizes the LUMO distribution,thereby stabilizing the LUMO energy level and reducing its π → π* transition gap.The maximum emission peak is observed at 520 nm,emitting yellow-green light with a PLQE of 13%.Overall,our molecular design and results on structure-property relationships can provide fundamental guidance for the design of phenothiazine derivatives with specific photoelectric performance.
维普
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