A solvatochromic study of silicates and borate containing 4-nitrocatechol ligands

摘要

Solvatochromism of 4-nitrocatechol (1), tetra-n-butylammonium 2-hydroxy-4-nitrophenolate (2), sodium tris(4-nitrobenzene-1,2-diolato)silicate (3a), tetra-n-butylammonium tris(4-nitrobenzene-1,2-diolato)silicate (3b), pyrrolidinium tris(4-nitrobenzene-1,2-diolato)silicate (3c), (3-amino-1-propyl)-bis(4-nitrobenzene-1,2-diolato)silicate (4a), and (N,N-diethyl-3-amino-1-propyl)-bis(4-nitrobenzene-1,2-diolato)silicate (4b) as well as potassium bis(4-nitrobenzene-1,2-diolato)borate (5) has been studied in a set of common solvents. The origin of the solvent-induced UV/vis band shifts of 1-3c, and 5 has been determined by means of Linear Solvation Energy Relationship (LSER) using the empirical Kamlet-Taft and Catalan solvent parameter sets, respectively. The solvent-induced UV/vis band shift of the negatively charged moiety of all solvatochromic dyes studied is mainly a function of the hydrogen-bond donor (HBD) strength and the dipolarity/polarizability of the solvent as shown by multiple regression analyses. HBD solvents cause a hypsochromic shift of the UV/vis band due to specific solvation of the anion site. Oppositely, increasing dipolarity/polarizability of the solvent induces a bathochromic shift of the UV/vis absorption band. The donor strength of the solvent has an influence on the UV/vis band shift since ion pair formation occurs in solvents of low relative permittivity. This is shown by the impact of the counter ion of sodium tris(4-nitrobenzene-1,2-diolato)silicate (3a) compared to tetra-n-butylammonium tris(4-nitrobenzene-1,2-diolato)silicate (3b). The influence of the counter ion on the position of the UV/vis absorption band occurs in the same way as HBD solvents do. Na+ and the pyrrolidinium ion, respectively, have a stronger influence than the tetra-n-butylammonium ion on the solvatochromic band shift due to the stronger cation-anion interaction. Copyright (C) 2008 John Wiley & Sons, Ltd.