Exciton-Coupled Circular Dichroism Characterization of Monotopically Binding Guests in Host-Guest Complexes with a Bis(zinc porphyrin) Tweezer.

ABSTRACT

A stiff-stilbene-linked bisporphyrin tweezer with inherent helicity was used for exciton-coupled circular dichroism (ECCD) characterization of a series of monotopically binding amine guest molecules. CD signals were observed for a variety of monoamines at relatively low tweezer/amine (host/guest) ratios between 1 10 to 1 70. For the amines producing the most intense CD signals, a binding stoichiometry of 1 2 was found. A likely explanation is the presence of guest-guest interactions in the complexes. This is supported by the correlation observed between CD signal intensity and magnitude of possible noncovalent binding between the guests, which can be divided into three groups showing no, moderate and strong response, respectively. Further support for this rationalization comes from molecular modelling.