A novel photo-active Cd:1,4-benzene dicarboxylate metal organic framework templated using [Ru(ii)(2,2′-bipyridine)3]2+: synthesis and photophysics of RWLC-5

Abstract

The development of photoactive porous materials is of significant importance for applications ranging from sustainable energy to pharmaceutical development and catalysis. A particularly attractive class of photo-active materials is the metal–organic framework (MOF)-based platform in which the photo-active elements are components of the framework itself or photo-active guests encapsulated within the MOF cavities. It has now been demonstrated that the photo-active [Ru(2,2′-bipyridine)₃]²⁺ (RuBpy) complex can template the formation of MOFs with varying three dimensional structures. Here we report the synthesis and structural and photo-physical characterization of a new RuBpy-templated MOF composed of Cd²⁺ ions with 1,4-benzenedicarboxylate ligands (RWLC-5) that contains crystallographically resolved RuBpy complexes. The new material displays a biphasic emission decay (130 ns and 1180 ns, T = 20 °C) and a bathochromically shifted emission maximum, relative to RuBpy in solution (603 nm for RuBpy in ethanol vs. 630 nm for RWLC-5). The emission lifetimes also do not display temperature-dependent decays which are characteristic of RuBpy type complexes as well as other RuBpy templated MOFs. The lack of temperature dependence is consistent with the complete deactivation of the ³LF state of the encapsulated RuBpy complex due to a constrained environment. The fast phase decay is attributed to a water molecule hydrogen bonded to a bipyridine ligand associated with ∼38% of the encapsulated RuBpy complexes resulting in the nonradiative deactivation of the ³MLCT state.