The critical role of the coordination sphere in the high-efficiency blue-light emission from aminopyrazine metal-organic polymers

Abstract

A cadmium coordination polymer assembled with aminopyrazine (ampyz) and acetate is known to convert UV radiation into blue light with external brightness of 75.4%. Here we prepared a novel light-emitting material based on this coordination polymeric framework by replacing the high-toxicity cadmium element to zinc. The novel photoluminescent material presented internal and external photoluminescence quantum yields (iPLQY and ePLQY) of 16.0% and 14.4%, respectively. This emission efficiency decrease in the zinc isomorph resulted from the cleavage of one acetate coordination bond since Zn2+ is smaller than Cd2+. The lack of this coordination bond results in poor orbital overlap and lower structural rigidity and then less efficient charge transfer and higher radiativeless decay. The reaction of zinc acetate dihydrate and ampyz originated also another coordination compound, which has however a discrete motif and lower iPLQY and ePLQY values of 6.6% and 5.9%, respectively. This study therefore expands our knowledge on the reasons behinds cadmium optimizing much the UV conversion efficiency of the ampyz framework.