Abstract
Abstract A cyclic diacetylene (XIa) has been synthesized by the oxidative coupling of 1, 5-bis(propargyloxymethyl)naphthalene (X) with a cyclic dimer (XIb) and a cyclic trimer (XIc). The electronic spectra of XIb and XIc have been found to be almost identical with that of naphthalene with respect to the location of the absorption maxima and the intensities. On the other hand, a marked decrease in the absorption intensities has been observed in the spectrum of the cyclic monomer (XIa). An inspection of the Dreiding model of XIa indicates that the two conformations (A and B) can retain the maximum distance between the dyine unit and the naphthalene nucleus. On the basis of the molecular model, the distance between the two chromophores and the angle between the short axis of the nucleus and the bridging chain have been estimated to be 2.26 Å, 21° for A and 2.12 Åand 38° for B. Employing these data, the hypochromic effect exerted by the diyne chromophore on the absorption of the naphthalene nucleus has been calculated according to the theory of Tinoco and Rhodes, resulting in a fairly good agreement with the observed values. Inversely, the calculation of the distance and the angle between the two chromophoric groups using the observed hypochromic effect has also given reasonable values. Therefore, the hypochromism observed in the cyclic diacetylene (XIa) has been attributed to the operation of dispersion-force interaction between diyne unit and the naphthalene chromophore.
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