A Pd3L6 supramolecular cage incorporating photoactive [2.2]paracyclophane units

Abstract

[2.2]Paracyclophane (pCp) scaffolds, unlike many π-conjugated building blocks, have been rarely explored in supramolecular self-assembly. Herein we report the synthesis and characterization of two ligands, pCpd3py and pCpd4py, composed of a pCp core functionalized at its 7- and 15-positions respectively with 3-pyridyl and 4-pyridyl units. The self-assembly of pCpd4py with Pd²⁺ metal ions afforded a [Pd₃(pCpd4py)₆]⁶⁺ cage structure, pCpd4py-Pd, where the six pCpd4py ligands doubly bridge each edge of the Pd₃ triangular core. The ligand pCpd4py and the palladium cage pCpd4py-Pd have been characterized by NMR spectroscopy, ESI-MS spectrometry and X-ray diffraction analyses and their photophysical properties investigated by steady-state and time-resolved emission spectroscopy as well as time-dependent density functional theory calculations.