ISSN:
0894-3230
Keywords:
supramolecular donor-acceptor complexes
;
dichlorofluorescein
;
cis- and trans-4,4′(N,N′-dimethylpyri- dinium)ethylene
;
Chemistry
;
Theoretical, Physical and Computational Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
---trans-4,4′(N,N′-Dimethylpyridinium)ethylene [trans-(1)] and cis-4,4′(N,N′-dimethylpyridinium)ethylene [cis-1] form with 2,7-dichlorofluorescein [DCF2-, (2)] donor-acceptor complexes of 1:1 stoichiometry [K(trans-1)=14 000 M-1 and K(cis-1)=300 M-1 in water]. The lower affinity of cis-1 to form the donor-acceptor complex with DCF2-, (2), is attributed to the non-planar structure of cis-1 (tilt-angle between the pyridinium rings=26°). The solid-state structure of the complex between DCF2- and trans-1 indicates alternate stacking of donor and acceptor units with an inter-layer spacing of 3·4 Å. Solubilization of the crystalline DCF2- and trans-1 complex in water or dimethylformamide (DMF) results in the initial formation of a non-symmetric complex where a trans-1 unit is inter-layered between two DCF2- components, and a second trans-1 unit is located externally to the supramolecular assembly and participates in charge neutralization [(DCF2-)2 · · · trans-1/trans-1]. The primary non-symmetrical complex is thermally transformed to a themodynamically stable symmetric complex where the DCF2- and trans-1 form a sandwich-type layered assembly [DCF2- · · · trans-1]. The structural features of the complexes were characterized by 1H-NMR spectroscopy. The kinetics of the transformation of the [(DCF2-)2 · · · trans-1/trans-1] complex to the [DCF2- · · · trans-1] assembly was spectroscopically characterized in DMF (k=0·22 s-1 at 322 K; Ea=20 kcal mol-1). © 1997 John Wiley & Sons, Ltd.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
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