ESR study of photoinduced defects in isotopically enriched quasi-one-dimensional chlorine-bridged platinum complexes

Photoinduced defects in the quasi-one-dimensional chlorine-bridged platinum complex, [Pt-II(en)(2)][Pt-IV(en)(2)Cl-2](ClO4)(4), where en=ethylenediamine, C2N2H8, were investigated by light-induced electron-spin resonance (LESR). Using samples prepared with enriched nuclear isotopes including Pt-194 (I = 0), H-2(I = 1), and Cl-37 (I = 3/2, magnetogyric ratio similar to 83% that of Cl-35), the hyperfine and superhyperfine (SHF) patterns in the LESR spectra were fully characterized. The SHF structure (16 G average spacing) is unequivocally assigned to the bridging chlorines by comparison of the LESR spectra from samples with natural abundance Cl with samples enriched with Cl-37. The LESR spectra were analyzed at g(perpendicular to),g(\\), and intermediate angles by simulation of both the polaron and soliton-spin distributions. The results at temperatures above 6 K were found to be in better agreement with the neutral soliton assignment advanced by Kuroda and co-workers, The spectra from 6 to 140 K do not indicate motional narrowing as has been previously suggested. Below 6 K, surprisingly, the LESR spectra of both the natural and isotopically enriched samples exhibit an unusual dependence on temperature, modulation frequency, or microwave power, which indicates the presence:of a localized dynamic process. Two other types of defect which exhibit strong sample-to-sample variability were also discovered in the LESR spectra: one is likely a spin triplet, and the other appears only at temperatures above approximately 120 K and is quite intense and stable at room temperature.