APPLICATION OF FLUORESCENCE TO ELUCIDATE THE GROUND-STATE ELECTRONIC-STRUCTURE OF BORON, ZINC AND ALUMINUM COMPLEXES OF 3,5-DI-TERT-BUTYLSALICYLIC ACID

The ground state electronic structure of boron, zinc and aluminum comp lexes of 3,5-di-tert-butylsalicylic acid (t-BSA) was studied by fluore scence spectroscopy. These compounds are negative charge control addit ives (CCAs) commercially known as LR120, Bontron E84 and Bontron E88 r espectively. They are synthesized by condensing the corresponding meta l salts with t-BSA and are primarily characterized by elemental analys is. Spectroscopic analysis, by IR and C-13 nuclear magnetic resonance (NMR), fails to provide adequate structural information on these mater ials. Are they salts or chelate complexes? Previous studies in our lab oratory have shown that lithium 3,5-di-tert-butylsalicylate (Lit-BSA) exhibits a characteristic, long-wavelength fluorescence. The Stokes sh ift (from peak to peak) is approximately 9300 cm(-1). In this work, we use the fluorescence of Lit-BSA as a probe of the ionicity of the dib utylsalicylato groups in LR120, Bontron E84 and Bontron E88 (in the gr ound state). Comparison of the fluorescence spectra reveals that the d ibutylsalicylato groups in LR120 are not ionic. In fact, they resemble an ester. We conclude that LR120 is a cyclic boron ester and that the B-O bond is covalent. The comparison also reveals that the dibutylsal icylato groups in Bontron E84 and Bontron E88 are ionic in both polar and non-polar solvents. The strong ionic character in non-polar solven ts, which differs from that of Lit-BSA, suggests that Bontron E84 and Bontron Ess are chelate complexes and that the di-tert-butylsalicylato groups are bidentate ligands for the Zn2+ and Al3+ ions respectively. The technological implications of the results obtained on the toner c harging mechanism are discussed. (C) 1997 Elsevier Science S.A.