DISCOTIC LIQUID-CRYSTALS OF TRANSITION-METAL COMPLEXES .17. THE MECHANISM OF MESOMORPHIC THERMOCHROMISM IN BIS(OCTASUBSTITUTED DIPHENYLGLYOXIMATO)PALLADIUM(II) COMPLEXES ESTABLISHED BY THEIR TEMPERATURE-DEPENDENT ELECTRONIC-SPECTRA

The bands in the electronic spectra of the [Pd{(C12O)4dpg}2] and [Pd{( C6)4dpg}2] complexes were assigned by using the results of temperature -dependent electronic spectral measurements. The temperature-dependent electronic spectra of ''cast samples'' of the complexes showed that t wo characteristic bands shift to higher energy (blue shift) with incre asing temperature. The band which is located at a longer wavelength wa s assigned to the 4d(z)2-5p(z) transition (d-p band), and that located at a shorter wavelength to the metal-to-ligand charge-transfer transi tion (MLCT band). The absorption intensities of both bands strongly de pend on the sample film preparation manners and temperatures. From the se facts, the mechanism of this unique ''mesomorphic thermochromism'' has been established.