Controlling the Photophysics of Aromatic Guests Using a Cyclic Porphyrin Dimer: Synthesis, Structure, and Encapsulation-Mediated “ON-OFF” Switch

Abstract

A cyclic zinc(II) porphyrin dimer with flexible linkers has been employed as an artificial molecular container that can efficiently encapsulate aromatic guests (pyrene/anthracene) through π–π interactions. Such molecular entrapment inside the container completely alters the photophysical pathways of the encapsulated guests that are normally favored in solution. As a consequence, the exciplex emission (in case of pyrene), and photodimerization (in case of anthracene) properties are suppressed inside the container. The structural integrity and compactness of the host–guest assemblies are the reason that prevents the guest molecules to come out from the container, thus switching “OFF” their favored solution pathways. The effects of such supramolecular encapsulation have been extensively investigated using UV/Visible, 1H NMR, fluorescence, and X-ray structure determination of the host–guest complexes. The high association constant for the complexes manifests the robust nature of the host–guest assemblies in solution. Moreover, the exciplex emission and photodimerization properties of the guests can be recovered by the addition of bidentate N-donor ligand (1,4-diazabicyclo[2.2.2]octane, DABCO), which immediately replaces the encapsulated guests by coordinating with the metal centers of the host. Such controllable and dynamic features of the bisporphyrinic container will further enhance the choice of incoming guest molecules and extend the range of various applications in supramolecular host–guest chemistry.