Photochromic transformations in solutions of thiuram disulfide and di-thiocarbamate Ni(II) complex in acetonitrile

The paper shows that the solutions of thiuram disulfide (tds = R2NC(S)S-S(S )CNR2, where R is the alkyl group (Me, Et, n-Pr and n-Bu)) and plane di-thi ocarbamate complex Ni(II) (Ni(dtc)(2), where the di-thiocarbamate anion dtc (-) = (R2NCS2-) in acetonitrile are the photochromic systems. Irradiation o f these solutions by the light pulse of an XeCl eximer laser (308 nm) cause s new absorption in the region of 350-650 nm which decays in the second tim e-range and the system returns to its initial state. The transformation cyc le may be performed repeatedly without degradation of spectral variations. Using laser flash photolysis, it is shown that the first transformation sta ge involves the dissociation of the excited thiuram disulfide molecule into two di-thiocarbamate radicals (dtc(.) radicals). These radicals coordinate with almost diffusion rate constant with Ni(dtc)(2) to form the Ni(dtc)(2) (dtc(.)) complex which possesses new absorption. The Ni(dtc)(2)(dtc(.)) com plex vanishes slowly by dissociation, resulting in a free dtc' radical form ation which either transforms into thiuram disulfide due to re-combination or reacts with the initial Ni(dtc)(2) complex, which again leads to Ni(dtc) (2)(dtc(.)) formation. The optical spectra of intermediates and the rate co nstants of all transformation stages of these particles have been determine d. (C) 1998 Elsevier Science S.A. All rights reserved.