Supramolecular donor-acceptor complexes of dichlorofluorescein and cis- and trans-4,4'-(N,N'-dimethylpyridinium)ethylene

trans-4,4'(N,N'-Dimethylpyridinium)ethyl [trans-(1)] and cis-4,4'(N,N'-dimethylpyridinium)ethylen [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 degrees). 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 Angstrom. 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 H-1-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; E-a=20 kcal mol(-1)). (C) 1997 by John Wiley & Sons, Ltd.