title: Electron delocalization in a rigid cofacial naphthalene-1,8:4,5-bis(dicarboximide) dimer.
abstract: Investigating through-space electronic communication between discrete cofacially oriented aromatic π-systems is fundamental to understanding assemblies as diverse as double-stranded DNA, organic photovoltaics and thin-film transistors. A detailed understanding of the electronic interactions involved rests on making the appropriate molecular compounds with rigid covalent scaffolds and π-π distances in the range of ca. 3.5 Å. Reported herein is an enantiomeric pair of doubly-bridged naphthalene-1,8:4,5-bis(dicarboximide) (NDI) cyclophanes and the characterization of four of their electronic states, namely 1) the ground state, 2) the exciton coupled singlet excited state, 3) the radical anion with strong through-space interactions between the redox-active NDI molecules, and 4) the diamagnetic diradical dianion using UV/Vis/NIR, EPR and ENDOR spectroscopies in addition to X-ray crystallography. Despite the unfavorable Coulombic repulsion, the singlet diradical dianion dimer of NDI shows a more pronounced intramolecular π-π stacking interaction when compared with its neutral analog.
authors.affiliation: Center for the Chemistry of Integrated Systems, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113 (USA); Argonne-Northwestern Solar Energy Research (ANSER) Center, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113 (USA).
authors.forename: Yilei
authors.initials: Y
authors.lastname: Wu
authors.forename: Marco
authors.initials: M
authors.lastname: Frasconi
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Gardner
authors.forename: Paul R
authors.initials: PR
authors.lastname: McGonigal
authors.forename: Severin T
authors.initials: ST
authors.lastname: Schneebeli
authors.forename: Michael R
authors.initials: MR
authors.lastname: Wasielewski
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart
mesh_terms: D019281:Dimerization; D004563:Electrochemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D009281:Naphthalenes / Q000737:chemistry*; D010084:Oxidation-Reduction; D013237:Stereoisomerism
chemical_list: D009281:Naphthalenes; C547163:naphthalene-1,8:4,5-bis(dicarboximide)
keywords: cyclophane; excimer emission; mixed-valence compounds; radical anion dimer; π-electron delocalization