ASSIGNMENT OF THE TRIPLET MANIFOLDS OF D(8) COMPLEXES AND LINEAR-CHAINS VIA THE EFFECTS OF TEMPERATURE AND MAGNETIC-FIELDS ON THE PHOSPHORESCENCE LIFETIMES

Characteristics of the electronic excited states of transition-metal c omplexes are reviewed. Attention is focussed on the experimental means of identifying the orbital natures of the emitting manifolds, Two new criteria for distinguishing among excited triplet terms are enunciate d: (a) the profile of the phosphorescence lifetime vs, the temperature in the range 77-4 K, and (b) the functional dependence of the phospho rescence decay rate on an external magnetic field at similar to 4 K te mperatures. These criteria are applied to the red emission emanating f rom solid platinum(II) complexes that form linear chains [Pt(2,2'-bipy ridine) (CN)(2); Pt(2,2'-bipyridine)Cl-2] and to Pt(2-phenylpyridine)( 2) that crystallizes with discrete dimeric units. The origin of the ph osphorescence from all three substances is assigned to a (3)d sigmap sigma term from a consideration of the criteria given above. The red e mission from solutions and rigid glasses of Pt (4,4'-dimethyl-2,2'-bip yridine) (ecda) and Pt(4,7-diphenyl-1,10-phenantroline) (ecda) [ecda = 1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolate] is reassigned to a ( 3)d sigmap sigma term of a binuclear defect state since the T-depende nce criterion does not support the current assignment to a (MLCT)-M-3 of a monomeric species. (C) 1998 Elsevier Science S.A.