PRESSURE-INDUCED LUMINESCENCE RIGIDOCHROMISM IN THE PHOTOPHYSICS OF THE CUPROUS IODIDE CLUSTER CU(4)I(4)PY(4)

The effect of applied hydrostatic pressure (up to 275 MPa) on the phot ophysical properties of the cuprous iodide cluster Cu(4)Lpy(4) (I) in room temperature solutions has been examined. Although there was littl e pressure effect on emission spectra or lifetimes under conditions wh ere the solutions remained fluid, dramatic hypsochromic shifts in the emission bands occurred when P exceeded that pressure necessary to ind uce the solvent to undergo the room temperature phase transition from fluid to solid (P-f). For example, in ambient pressure benzene, the la mbda(max)(em) of the ''cluster-centered'' (CC) emission of I is 695 Mt , but at P greater than or equal to P-f (72 MPa) this shifts to 575 nm , similar to the lambda(max)(em) seen for solid I (580 nm). In contras t to the pressure-induced rigidochromism displayed by the luminescence spectrum of I, the emission lifetimes proved relatively insensitive t o P. Notably, the CC state of Cu(4)L(4)py(4) represents an unusual ex ample displaying rigidochromism but not solvatochromism in its lumines cence. For comparison, analogous pressure studies were also carried on Re(phen)(CO)(3)Br, a complex which exhibits rigidochromism in lumines cence from a metal-to-ligand charge transfer state.