Luminescence lifetime up to microseconds in new coordination compounds with aminopyrazine and acetate

Abstract

Aminopyrazine (ampyz) and cadmium acetate assemble into a potent blue light emitting one-dimensional co- ordination polymer upon UV excitation. Here we were devoted to the replacement of cadmium in this optical material given its environmental and human health drawbacks. Three new ampyz-based coordination com- pounds were prepared and elucidated structurally, and had their light emission investigated upon UV excitation. The dihydrate crystal form of the discrete compounds [Co(ampyz)2(AcO)2(H2O)2] and [Ni(ampyz)2(A- cO)2(H2O)2] reveal to be isostructural themselves and to Zn2+ and Mn2+ versions thereof. Compound [Ag (ampyz)(AcO)]n(H2O)n assembles into polymeric one-dimensional coordination chains which are strongly bonded to each other through π...π interactions, hydrogen bonding and intermetallic bonds. Despite of their negligible emission power, their found luminescence lifetimes presented values up to 6 times greater than the previously reported parent complex, which can be correlated to the presence and strength of π...π stacking in- teractions. The Ag+ compound has the shortest π...π interactions measuring 3.415 Å, with the emission lifetime in the μs order. However, these intermolecular contacts seem be responsible to quench the emission power together with intrinsic electronic features probed by TD-DFT. The electronic transitions responsible for UV excitation exhibit low oscillator strengths due to the orthogonality of the donor and acceptor orbitals, receiving significant metal d contribution besides enrolment of single-coordinated acetate ligand.