Impact of substituents on luminescence and mechanochromism of two novel monometallic copper(I) complexes

Two new mononuclear Cu(I) complexes, [Cu(cbpy)(BINAP)]ClO4 (1) and [Cu(mcbpy)(BINAP)]ClO4 (2), have been synthesized and characterized (cbpy = 6-cyano-2,2ʹ-bipyridine, mcbpy = 4,4ʹ-dimethyl-6-cyano- 2,2ʹ-bipyridine, BINAP = 2,2ʹ-bis(diphenylphosphino)-1,1ʹ-binaphthyl). Both Cu(I) complexes are photo- luminescent in the solid state at ambient temperature, with similar emission bands at 620 and 601 nm, respectively. Complex 2 exhibits the mechanochromic luminescence behavior with emission color changing from orange to orange-red, which is mainly due to the breakage of multiple CH⋯O hydrogen bonds between mcbpy-CH and counter-ion ClO4− under grinding. In contrast, the mechanochromic luminescence is not observed in 1 with much weaker cbpy-CH⋯O hydrogen bonds than those of 2. These clearly suggest that the methylation of 2,2ʹ-bipyridyl has an important effect on the mechanochromic luminescence properties of Cu(I) complexes. In addition, the potential applications of 2 have been investigated.