The luminescence rigidochromic effect exhibited by organometallic complexes: Rationale and applications

Several transition-metal organometallic complexes exhibit an especially pronounced hypsochromic shift of their luminescence bands when their solution environment becomes more rigid. This unusual spectroscopic effect has been termed ''luminescence rigidochromism'' and is apparently confined to metal-to-ligand charge-transfer excited states. Attention is drawn here to the types and photophysical characteristics of organometallic complexes that demonstrate this phenomenon and its underlying causes. Recently, a number of practical applications have arisen based on the luminescence rigidochromic effect; these involve a variety of material processes, including thermal and photochemical polymerizations and the sol-gel process. In each case an organometallic complex has been incorporated as a spectroscopic probe to monitor the large environmental changes that occur.