SUPRAMOLECULAR DONOR–ACCEPTOR COMPLEXES OF DICHLOROFLUORESCEIN AND cis- AND trans-4,4′-(N,N′-DIMETHYLPYRIDINIUM)ETHYLENE

✍ Scribed by Itamar Willner; Sharon Marx-tibbon; Shmuel Cohen; Yoav Eichen; Menachem Kaftori

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 191 KB
• Volume: 10
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199706)10:6<435::aid-poc903>3.0.co;2-2

✦ Synopsis

trans-4,4Ј(N,NЈ-Dimethylpyridinium)ethylene [trans-(1)] and cis-4,4Ј(N,NЈ-dimethylpyridinium)ethylene [cis

-1] form with 2,7-dichlorofluorescein [DCF 2 Ϫ , (2)] donor-acceptor complexes of 1:1 stoichiometry [K(trans-1) = 14 000 M Ϫ 1 and K(cis-1) = 300 M Ϫ 1 in water]. The lower affinity of cis-1 to form the donor-acceptor complex with DCF 2 Ϫ , (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 DCF 2 Ϫ and trans-1 indicates alternate stacking of donor and acceptor units with an inter-layer spacing of 3•4 Å. Solubilization of the crystalline DCF 2 Ϫ 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 DCF 2 Ϫ components, and a second trans-1 unit is located externally to the supramolecular assembly and participates in charge neutralization [(DCF 2 Ϫ ) 2 • • • trans-1/trans-1]. The primary non-symmetrical complex is thermally transformed to a themodynamically stable symmetric complex where the DCF 2 Ϫ and trans-1 form a sandwich-type layered assembly [DCF 2 Ϫ • • • trans-1]. The structural features of the complexes were characterized by 1 H-NMR spectroscopy. The kinetics of the transformation of the [(DCF 2 Ϫ ) 2 • • • trans-1/trans-1] complex to the [DCF 2 Ϫ • • • trans-1] assembly was spectroscopically characterized in DMF (k = 0•22 s Ϫ 1 at 322 K; E a = 20 kcal mol Ϫ 1 ).