Electroluminescent properties of dimeric bis(2-(2′-hydroxyl phenyl)benzthiazolate)zinc (II) complex

A blue shifted photoluminescent emission in bis(2-(2′-hydroxyl phenyl)benzthiazolate)zinc (II) complex, ZBZT, arises out of the dimeric structure, typical of the localized electron density around the non-bridged ligand in the excited state of the complex. An average decay lifetime of 4.8 and 3.0 ns for the ligand and the complex, respectively indicates an energy transfer from the ligand to the metal. A PL quantum efficiency of about ϕZBZT=0.45 in DMF solution is observed, in comparison to the Alq3, complex, ϕAlq3=0.116. Semi empirical ZINDO/S-SCF-CI calculations support the dominance of non-bridged ligand moiety in controlling the photoluminescent properties. An unusually broad white light (FWHM ∼220 nm) electroluminescent emission in the two layer device structure brings out the features of an exciplex formation between the active layer ZBZT/TPD interface, which is studied at different current densities. Such a broadened emission is verified for different thicknesses of the active layer substantiating the role of exciplex formation.