PHOTOCHEMICAL-REACTIONS OF RHODIUM(III) DIIMINE COMPLEXES IN SOLID GLYCEROL MATRICES - THERMAL-ACTIVATION OF A TRIPLET DD LEVEL FROM A TRIPLET PI-PI-ASTERISK MANIFOLD

At temperatures below 150 K in rigid glycerol glasses, [Rh(III)(s-NN)( 3)](PF6)(3) complexes display a (3) pi pi phosphorescence characteris tic of the s-NN ligand [s-NN = 1,10-phenanthroline (phen), 4-Mephen, 4 ,7-Me-2-phen, and 3,4,7,8-Me(4)phen]. Above 150 K but below the meltin g point of glycerol, a temperature-dependent first-order reaction occu rs. The temperature dependences of these photochemical reactions confo rm to the Arrhenius equation with an activation energy range of 2500-3 800 cm(-1). These results are interpreted in terms of the thermal redi stribution of energy from the unreactive (3) pi pi excited term to a close-lying chemically active (3)dd level. The relationship of the Arr henius activation energies to the electronic structures and the spectr a of the parent complexes is discussed. At 77 K all the photoproducts emit 3 pi pi(-->)gs phosphorescence. The spectral characteristics of the photogenerated species indicate that a single product has been pro duced in every case. Moreover, the energy of the phosphorescence of ea ch photoproduct and its decay time at 77 K indicate that the newly gen erated species contains a monodentate s-NN ligand. We conjecture that one octahedral site on the metal is occupied by a glyceroxide moiety t hat is bonded directly to the rhodium ion through the oxygen atom.