Switching from sky blue to deep green fluorescent Zn(II) complexes for OLEDs applications

Abstract

Three new Zn(II) 4′-aryl substituted 2,2′:6′,2′-terpyridine (terpy) complexes of the type [Zn(Ln)2]NO3 complexes (where, L1 = 4′-(4-methylphenyl)−2,2′:6′,2′-terpyridine, L2 = 4′-(3,4,5-trimethoxyphenyl)−2,2′:6′,2′-terpyridine, and L3 = 4′-(2-thiophenyl)−2,2′:6′,2′-terpyridine) were successfully synthesized and photophysical characterizations were done for OLEDs applications. The UV–visible absorption spectra of the complexes exhibited an intense absorption band in the range of 240–380nm owing to a spin-allowed intraligand (π–π*) charge transition. The addition of an electron-donating aryl substituent into the terpy ligand within the complexes induced a significant red-shift of the spectrum. A solid state photoluminescence (PL) analysis revealed a transition from sky blue to green, while the complexes in the DMSO solution which possessed the most emissions appeared sky to deep blue, respectively. A cyclic voltammetry investigation of the complexes revealed a quasi-reversible reduction where the estimated electrochemical data concurred with theoretical calculations. Moreover, the complexes showed an optical band gap of 3.40–3.51eV and a HOMO level from –6.64 to −6.47eV. In addition, all the complexes depicted an excellent thermal stability. Hence, the presented complexes are promising candidates for blue and green fluorescent OLEDs application as electron transport as well as electroluminescent material.