The effect of applied hydrostatic pressure (up to 275 MPa) on the photophysical properties of the cuprous iodide cluster Cu(4)Lpy(4) (I) in room temperature solutions has been examined. Although there was little pressure effect on emission spectra or lifetimes under conditions where the solutions remained fluid, dramatic hypsochromic shifts in the emission bands occurred when P exceeded that pressure necessary to induce the solvent to undergo the room temperature phase transition from fluid to solid (P-f). For example, in ambient pressure benzene, the lambda(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 contrast to the pressure-induced rigidochromism displayed by the luminescence spectrum of I, the emission lifetimes proved relatively insensitive to P. Notably, the CC* state of Cu(4)L(4)py(4) represents an unusual example displaying rigidochromism but not solvatochromism in its luminescence. For comparison, analogous pressure studies were also carried on Re(phen)(CO)(3)Br, a complex which exhibits rigidochromism in luminescence from a metal-to-ligand charge transfer state.