Synthesis and Luminescence of Optical Memory Active Tetramethylammonium Cyanocuprate(I) 3D Networks

The structures of three tetramethylammonium cyanocuprate(I) 3D networks [NMe ] [Cu(CN) ] •0.25H O ( ), [NMe ][Cu (CN) ] ( ), and [NMe ][Cu (CN) ] ( ), (Me N = tetramethylammonium), and the photophysics of and are reported. These complexes are prepared by combining aqueous solutions of the simple salts tetramethylammonium chloride and potassium dicyanocuprate. Single-crystal X-ray diffraction analysis of complex reveals {Cu (CN) ( -CN) } rhomboids crosslinked by cyano ligands and D {Cu(CN) } metal clusters into a 3D coordination polymer, while features independent 2D layers of fused hexagonal {Cu (CN) } rings where two Cu(I) centers reside in a linear C coordination sphere. Metallophilic interactions are observed in as close Cu⋯Cu distances, but are noticeably absent in . Complex is a simple honeycomb sheet composed of trigonal planar Cu(I) centers with no Cu Cu interactions. Temperature and time-dependent luminescence of and have been performed between 298 K and 78 K and demonstrate that is a dual singlet/triplet emitter at low temperatures while is a triplet-only emitter. DFT and TD-DFT calculations were used to help interpret the experimental findings. Optical memory experiments show that and are both optical memory active. These complexes undergo a reduction of emission intensity upon laser irradiation at 255 nm although this loss is much faster in . The loss of emission intensity is reversible in both cases by applying heat to the sample. We propose a light-induced electron transfer mechanism for the optical memory behavior observed.