Mechanochromic luminescent materials of bimetallic Cu(i) complexes showing thermally activated delayed fluorescence

Mechanochromic luminescence has recently received increasing interest due to its promising applications. Herein we report a new series of ionic bimetallic Cu(i) complexes exhibiting reversible mechanochromic luminescence and thermally activated delayed fluorescence. These Cu(i) complexes possess one emissive [{Cu((NN)-N-boolean AND)}(2)(mu-dppm)(2)](2+) cation with two N-H groups in two functional 3-(2 '-pyridyl)pyrazole ((NN)-N-boolean AND) ligands, and each N-H proton forms a N-HMIDLINE HORIZONTAL ELLIPSISO hydrogen bond with one O atom of a counterion ClO4-. It is shown that reversible mechanochromic luminescence is relevant to the breaking and restoring of the NHMIDLINE HORIZONTAL ELLIPSISO hydrogen bonds controlled by mechanical grinding and CH2Cl2 vapor, which is well supported by their FT-IR analyses. Importantly, the difference of those two inter-convertible luminous colors appearing in luminescence mechanochromism can be effectively regulated by altering the electronic nature of the substituent on the pyrazole ring such as the trifluoromethyl and tert-butyl. This clearly suggests that rationally designed Cu(i) luminescent complexes can become promising candidates for developing low-cost intelligent responsive luminescence materials.