Rigidochromism of tetranuclear Cu(I)-pyrazolate macrocycles: steric crowding with trifluoromethyl groups.

Macrocyclic Cu(I)-pyrazolate tetramers (Cu 4 pz 4 ) can fold into compact structures with luminescent Cu 4 cores whose emission wavelengths are sensitive to steric effects along the periphery of the macrocycle. Introducing CF 3 at the C4 position of 3,5-di- t Bu-pyrazolate increases steric crowding that modifies the conformational behavior of the Cu 4 pz 4 complex, highlighted by a low-temperature martensitic transition. Variable-temperature analysis of solid-state luminescence reveal an unexpected blueshifting of emission with rising temperature.