Synthesis and excited-state properties of rhodium(III) terpyridine complexes

Reported are the photophysical properties of several previously known and newly synthesized rhodium(III) complexes of 2,2':6',2 -terpyridine: Rh(trpy){sub 2}{sup 3+}, Rh(trpy)(bpy)(py){sup 3+}, and Rh(trpy)(bpy)Cl{sup 2+} (bpy = 2,2'-bipyridine; py = pyridine). The absorption spectrum of each of these complexes in aqueous solution is dominated by intraligand {pi}{sub L}-{pi}{sub L}* transitions that obscure the regions where ligand field (LF) bands would be expected. However, the luminescence spectra both in ambient-temperature fluid solutions and in 77 K glasses show broad, Gaussian-shaped bands interpreted to be the result of emission from the lowest energy triplet ligand field states. Photolysis of Rh(trpy)(bpy)Cl{sup 2+} in aqueous solution leads to photolabilization of Cl{sup {minus}}, as seen with other Rh(III) chloro amine complexes; however, the quantum yield proved to be quite small (0.002 mol/einstein), a feature that can be attributed to an unusually small rate constant for Cl{sup {minus}} labilization from the {sup 3}LF* state. 20 references, 1 figure, 3 tables.