LINEAR AND STACK OLIGOSTREPTOCYANINES - EFFECTS OF RELATIVE ORIENTATION OF CHROMOPHORES ON REDOX POTENTIALS OF DYE AGGREGATES

Linear and stack pentamethinestreptocyanine oligomers were prepared in which streptocyanines are covalently connected to each other. The abs orption bands of the linear oligomers showed bathochromic shifts compa red to that of the corresponding monomer, while the absorption band of the stack dimer was hypsochromically shifted. These spectral shifts w ere reproduced by a calculation with the INDO/S-CI method and are in a greement with those based upon a molecular exciton theory. The redox p otentials of the linear oligomers underwent a positive shift due to th e Coulombic interaction compared to those of the streptocyanine monome r The positive shift of the reduction potential and the negative shift of the oxidation potential of the stack dimer are explained in terms of the Coulombic and orbital interactions.