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A series of tetracoordinated boron complexes derived from various 1,j-diketones and bidentate ligands (oxalato, malonato, catecholato and difluoro) were prepared. Their absorption, fluorescence and phosphorescence spectra, a t ambient temperature and 77 K, and cyclic voltammmetry in acetonitrile were studied. The boron complexes exhibited high molar absorptivity and fluorescence intensities as compared with the parent diketones; the phenomena are in agreement with the lowest singlet excited state possessing the z, z,* configuration with a rigid chelate structure. The redox potential differences correlate linearly with the lowest singlet (E,) as well as the triplet (ET) excited state energy with slopes lower than unity. These linear correlations re-state that the electron exchange and Coulombic integral also vary proportionally to the potential differences. From these correlations, it is possible to determine E , and E , of those boron complexes that do not give fluorescence and phosphorescence.

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Ahstract-Each of the four isomeric biliverdin dimethyl esters of the IX series give a fluorescent spectrum at ambient temperature, the intensity of which increases considerably when these biliverdins are complexed with zinc. A systematic study of the influence of protic and aprotic solvents failed to yield significant results. In methanol. variations in the pH greatly affect the emission absorption spectra of zinc complexes of biliverdins.