摘要：

Dyes of the 3,3-diethylthiacyanine series dimerize over a certain concentration range, as shown by their adherence to the law of mass action for the monomer-dimer equilibrium. At higher concentrations, a more complex H-aggregate appears. The stability of the dimers, as measured by the free energy of dimerization, increases steadily with chain length. The dimeric spectrum consists of an intense P-branch, hypsochromic to the monomeric maximum, and a feeble, bathochromic N-branch. The monomers are linked with their molecular planes and chromophores approximately parallel. Mixed dimers, with relatively strong N-branches, are formed in aqueous solutions of certain dye pairs. The significance of dimerization with respect to fluorescence quenching, photochemical activity, and the "excimer" is discussed.

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