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 240–380 nm 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 3.40–3.51 eV and a HOMO level from –6.64 to −6.47 eV. 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.