Analysis of Coherent Heteroclustering of Different Dyes by Use of Threoninol Nucleotides for Comparison with the Molecular Exciton Theory

To test the molecular exciton theory for heterodimeric chromophores, various heterodimers and clusters, ill which two different dyes were stacked alternately, were prepared by hybridizing two oligodeoxyribonucleotides (ODNs). each of which tethered a different dye on D-threoninol at the center of the strand. NMR analyses revealed that two different dyes Irons each strand were stacked antiparallel to each other in the duplex, and were located adjacent to the 5'-side of a natural nucleobase. The spectroscopic behavior of these heterodimers wits systematically examined as it function of the difference in the wavelength of the dye absorption maxima (Delta lambda(max)). WC found that the absorption spectrum of the heterodimer was significantly different from that of the simple sum of each monomeric dye in the single strand When azobenzene and Methyl Red, which have at 335 and 490 nm, respectively, in the single strand (Delta lambda(max) = 144 nm), were assembled on ODNs, the bared derived from azobenzene exhibited a small hyperchromism. whereas the baled front,Methyl Red showed hypochromism and both bands shifted to a longer wavelength (bathochromism). These hyper- and hypochromisms were further enhanced ire a heterodimer derived from 4'-methylthioazobenzene: and Methyl Red, which had a much smaller Delta lambda(max) (82 nm: lambda(max) = 398 and 40 nm in the single-strand, respectively). With a combination of 4'-dimethyl-amino-2-nitroazobenzene and Methyl Red, which had an even smaller Delta lambda(max) (33 nm). a single sharp absorption baled that was apparently different from the SLIM of the. single-stranded spectra was observed. These changes ill the intensity of the absorption hand could he explained by the molecular exciton theory, which has been mainly applied to the spectral behavior of H- and/or J-aggregates composed of homo dyes. However, the bathochromic band shifts observed at shorter wavelegths did clot agree with the hypsochromisms predicted by the theory. Thus. these data experimentally verify the molecular exciton theory of heterodimerization This Coherent coupling anion, the heterodimers could also partly explain the bathochromicity and hypochromicity that were observed when the dyes were intercalated into the duplex.