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.
' Data in parentheses are corrected for the percentage of cis-enol tautomer' by dividing the experimental E,,, by this percentage.
' In dichlorornethane.
Unless stated otherwise, spectra were recorded in acetonitrile.
In cyclohexane. In 1,2-dichloroethane. Percentage in acetonitrile of cis-enol tautomer unknown.
' Measured incyclohexane.
' Dibenzoylmethanatoboron diacetate; the data are cited from Ref. 6a. Calculated from equations obtained from regression analysis of Figure ; E, =0.54 + 0,84(EOy -Ewd); E, = 0.89 + 0,53(E,, -Ecd).
Fluorescenceyields notmeasured.