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Spectroscopic studies of the intermolecular interactions of a bis-azo dye, Direct Blue 1, on di- and trimerization in aqueous solution and in cellulose

Abbott, L.C., Batchelor, S.N., Oakes, J., Lindsay Smith, J.R. and Moore, J.N. (2004) Spectroscopic studies of the intermolecular interactions of a bis-azo dye, Direct Blue 1, on di- and trimerization in aqueous solution and in cellulose. Journal of Physical Chemistry B, 108 (36). pp. 13726-13735. ISSN 1089-5647

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Abstract

The intermolecular interactions of the bis-azo dye Direct Blue 1 (Chicago Sky Blue 6B) have been studied as a function of concentration in aqueous solution and in cellophane using UV−visible absorption, NMR, and resonance Raman spectroscopy. UV−visible spectroscopy indicates that dimerization occurs in aqueous solution (Kdim ≈ 77 000 dm3 mol-1 at I = 0.01) and that it occurs more readily at higher ionic strength, where trimerization also occurs (Kdim ≈ 580 000 dm3 mol-1 and Ktrim ≈ 2700 dm3 mol-1 at I = 0.1); the driving force is enthalpic rather than entropic (ΔHdim ≈ −53 kJ mol-1 and ΔSdim ≈ −90 J K-1 mol-1 at I = 0.01). Dimerization occurs much less readily in cellophane (Kdim ≈ 42 dm3 mol-1) than in aqueous solution, indicating that strong dye−cellulose interactions compete effectively with dye−dye interactions. NMR spectroscopy indicates that Direct Blue 1 molecules interact by π-stacking at the central biphenyl group, while resonance Raman spectroscopy indicates that the internal structure and bonding of the monomers is essentially retained on stacking. The UV−visible spectra are consistent with this interpretation, and the application of exciton theory indicates that stacking results in angles between adjacent molecules which are different in the dimer (θ ≈ 84°) and trimer (θ ≈ 58°); they are attributed to geometries which minimize the repulsion between charged naphthylsulfonate groups.

Item Type: Article
Institution: The University of York
Academic Units: The University of York > Chemistry (York)
Depositing User: York RAE Import
Date Deposited: 15 Jun 2009 11:58
Last Modified: 15 Jun 2009 11:58
Published Version: http://dx.doi.org/10.1021/jp0485542
Status: Published
Publisher: American Chemical Society
Identification Number: 10.1021/jp0485542
URI: http://eprints.whiterose.ac.uk/id/eprint/6853

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