Synthesis of covalently linked ferric tris(bipyridil) - viologen molecule and photo coloration in poly(vinylalcohol)

Three types of ferric tris(bipyridil) complexes appended a viologen, 1(3+), 2(3+), 3(3+), each having methylene, ethylene, and butylene spacer between ferric tris(bipyridil)- and viologen units, were synthesized and their pho toinduced coloration properties were investigated in the thin poly(vinylalc ohol) films. Upon photoirradiation, the colorless film of 1(3+) turned to r ed with increase in the absorption intensity around 530 nm, ascribing the f errous tris(bipyridil) [Fe(II)bipy(3)] complex. The coloration is interpret ed in terms of the intramolecular electron transfer from the photogenerated viologen radical cation to the colorless Fe(III)bipy(3), since very little coloration of 4(3+) which has no viologen unit in a molecule was observed even in the presence of N, N'-dipropylviologen. Similar trends of 1(3+) wer e observed for 2(3+) and 3(3+). The order of absorption intensity around 53 0 nm is 1(3+) > 2(3+) > 3(3+), indicating that the electron transfer from t he photogenerated viologen radical cation to Fe(III)bipy(3) is achieved eff ectively for the complex with a short alkyl spacer. (C) 1999 Elsevier Scien ce S.A. All rights reserved.