RED-SHIFTED EMISSION-SPECTRA OF SEVERAL MESOSUBSTITUTED COPPER PORPHYRINS IN FLUID SOLUTION

Medium dependence of the emission spectra of several meso-substituted copper porphyrins was studied at 300-77 K. Copper porphyrins emit from the lowest excited (porphyrin triplet) states in fluid solution as we ll as in rigid media. Emission spectra of several copper porphyrins in toluene liquid solution were red-shifted from those in rigid media su ch as PMMA (poly(methylmethacrylate)) film. The copper porphyrins, whi ch give red-shifted emission in toluene solution, have (2,4)[b(1) (3)( a(2u)e(g))] configuration in the lowest excited states and the amount of the shift depends on meso-substituents ranging up to 1300 cm(-1). A s the emission spectra in toluene rigid glass at 77 K coincide with th ose in PMMA film, the observed shift in (2,4)[b(1) 3(a(2u)e(g))]-type porphyrins is attributable to distortion of the excited molecules in f luid solution. T(2,4,6-(MeO)(3))PPCu, in which bulky meso-substituents are likely to suppress torsion of the phenyl rings and distortion of the porphyrin plane, was found to show no shift of emission spectra, i n spite of the (2,4)[b(1) (3)(a(2u)e(g))] configuration. In the case o f TPrPCu, which has no phenyl group, red shift occurs as a result of t he medium being changed to become non-rigid. An out-of-plane distorted structure is proposed. Lifetimes of the emission in toluene solution are remarkably shorter in the copper porphyrins that show a larger emi ssion red-shift from the emission in PMMA film. This relation suggests that the distortion modes are connected with enhancement of the radia tionless decay.