Interplay of the Cu⋯Cu distance and coordination geometry as a factor affecting the quantum efficiency in dimeric copper(i) halide complexes with derivatives of 4-pyrazolylpyrimidine-2-thiol

electron-phonon coupling, which substantiates the higher photoluminescence quantum yield (PLQY) of [Cu2(LH)2I2] (form II) (Cu⋯Cu 2.65 Å) compared to that of [Cu2(LH)2I2] (form I) (Cu⋯Cu 2.86 Å).