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

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