Extrinsic vs. intrinsic luminescence and their interplay with spin crossover in 3D Hofmann-type coordination polymers

Abstract

The research of new multifunctional materials, as those undergoing spin crossover (SCO) and luminescent properties, is extremely important in the development of further optical and electronic switching devices. As a new step towards this ambitious aim, the coupling of SCO and fluorescence is presented here following two main strategies: whether the fluorescent agent is integrated as a part of the main structure of a 3D SCO coordination polymer {Fe^II(bpan)[M^I(CN)₂]₂} (bpan = bis(4-pyridyl)anthracene, M^I = Ag (FebpanAg), Au (FebpanAu)) or is a guest molecule inserted within the cavities of the 3D switchable framework {Fe^II(bpb)[M^I(CN)₂]₂}·pyrene (bpb = bis(4-pyridyl)butadiyne, M^I = Ag (FebpbAg·Pyr), Au (FebpbAu·Pyr)). The magnetic, calorimetric, structural, UV-Vis absorption and fluorescent characterizations were performed confirming the occurrence of a SCO-fluorescence interplay in the studied compounds. Moreover, the relevance of the intrinsic or extrinsic nature of the luminescence on the efficiency of the interplay is discussed on the basis of the available information.