Linear solvation energy (LSE) correlations of the solvatochromic response and x-ray structure analysis of hydrophilically N-substituted Michler's ketone derivatives

Bathochromic UV-Vis spectral shifts of two hydrophilically N-substituted Michler's ketone derivatives, 4,4'-bis[di(2-hydroxyethyl)amino]benzophenone [MK(OH)(4)] (I) and 4-(dimethylamino)-4'-[di(2-hydroxyethyl)-amino]benzophenone [MK(OH)(2)] (3), were measured in 28 solvents of different polarity. For MK(OH)(4) and MK(OH)(2) in non-polar, dipolar aprotic and hydrogen-bonding solvents, the solvatochromic responses of the two solutes conform exactly to the requirements of the Kamlet-Taft linear solvation free energy model of solvent-solute interactions. The contribution of the hydrogen-bond accepting property of the solvent on the bathochromic band shift of MK(OH)(4) and MK(OH)(2) increases with increasing number of their OH groups at the N-substituent. The x-ray crystallographic analysis for MK(OH)(2) reveals the presence of strong intermolecular hydrogen bonds between the carbonyl oxygen atom and the 2-hydroxyethyl group, which plays a significant role in the colour of the crystals. Copyright (C) 2001 John Wiley & Sons, Ltd.