Photochemistry and Photophysics of Coordination Compounds

Photochemistry and Photophysics of Coordination Compounds: Copper 103
Fig. 31 Temperature dependence of the emission spectrum of Cu4I4(4 – phenylpyridine)4
in toluene solution with relative intensities normalized to 1 in each case (Reprinted
from [147] with permission, © (1991) American Chemical Society)
orbitals do not interact and the CC emission bands are not observed [148]. In
Fig. 32 the relative position of the above-described excited states is schematically
represented by means of potential energy curves.
When the amine aromatic ligand py is replaced by the aliphatic one piperidine
(pip), the corresponding cluster Cu4I4(pip)4 preserves the CC band but
does not display the high energy XLCT emission owing to the absence of ligands
possessing π orbitals. Thus, luminescence thermochromism is the norm
for Cu4I4L4 clusters, but only when L is π-unsaturated.
Another factor contributing to the complicated pattern of the luminescence
properties of Cu4I4(4-phenylpyridine)4 is the dramatic red-shift of the
CC band in going from solid or frozen solution samples to fluid solutions, indicating
that also rigidochromism effects are operative. Ab initio calculations
and the Stokes shifts for Cu4I4(4-phenylpyridine)4 (up to 16 300 cm –1 for the
CC band in 296 Ktoluenesolution;7600 cm –1 for the XLCT band under the