Synthesis of dual emitting iodocuprates: can solvents switch the reaction outcome?

A remarkable effect of solvents on the reaction outcome has been discovered in the synthesis of halocuprates, as exemplified by the reaction of CuI with 1-methyl-2-methylthiopyridinium iodide, (Me–PySMe)I. When performed in acetonitrile, the reaction results in the selective self-assembly of iodocuprate (Me–PySMe)n[Cu2I3]n (1) featuring 1D double-stranded [Cu2I3]n ribbons. Surprisingly, upon exploiting acetone as a medium under other conditions being similar, isomeric 1D iodocuprate 2 containing one-stranded [Cu2I3]n chains is quantitatively formed. Iodocuprate 1 displays outstanding dual luminescence expressed by two emission bands at λmax = 680 and 550 nm, probably originating from the excited states of the cluster-centered (3CC) type and iodocuprate-to-cation charge transfer one, respectively. The resulting emission color of 1, being defined by the ratio of these bands, reversibly varies as a function of temperature spanning from deep-red (300 K) to yellow (77 K). Isomer 2, being also dual emissive, does not exhibit prominent thermochromic luminescence.