A series of new π-stacked compounds, 1,8-bis­(2′,5′-dimethoxybenzene-1′-yl)­naphthalene (1), 1,4-bis­(8′-(2″,5″-dimethoxybenzene-1″-yl)­naphthalen-1′-yl)­benzene (2), and 1,8-bis­(4′-(8″-(2‴,5‴-dimethoxybenzene-1‴-yl)­naphthalen-1″-yl)­benzene-1′-yl)­naphthalene (3), have been synthesized and characterized herein as precursor molecules of monocationic mixed-valence systems (MVSs). The three-dimensional geometries of these compounds were determined by X-ray crystallography. A near-orthogonal alignment of the naphthalene pillaring motif to the dimethoxybenzene redox center, or the phenylene spacer, imposes cofacial alignment of these units in a juxtaposed manner with sub-van der Waals interplanar distances. Cyclic and differential pulse voltammograms reveal that the ΔE values between two sequential oxidation potentials are 0.30, 0.11, and 0.10 V for 1, 2, and 3, respectively. MVSs derived from these compounds are recognized as class II according to the Robin and Day classification. The decay parameter β, which describes the distance dependence of the squared electronic coupling in the three mixed-valence systems, was experimentally determined via Mulliken–Hush analysis of the intervalence charge transfer band (β = 0.37 Å–1) and theoretically assessed from charge-resonance contributions derived from DFT computations (β = 0.37 Å–1). These values are extraordinarily mild, indicating that the electronic interaction between redox centers in the longitudinal direction may be comparable to that in the transverse direction, if the MVS system is appropriately designed.

A new π‐stacked compound, 1,8‐bis(2′,5′‐dimethoxy‐4′‐methyl‐[1,1′‐biphenyl]‐4‐yl)naphthalene (1) has been synthesized and characterized as a precursor molecule of monocationic mixed‐valence system (MVS). Cyclic and differential pulse voltammograms reveal that the ΔE°ox value between two sequential oxidation potentials is 163 mV. The three‐dimensional geometries of 1, 1•+, and 12+ were obtained via using density functional theory (DFT) calculations with a range‐separated hybrid functional and dispersion corrections (LC‐wPBE‐D3). Two dimethoxytoluene redox centers were aligned in parallel with van der Waals interplanar distances (3.50–3.70 Å). The electronic coupling in this MVS was evaluated by two different approaches: (1) Mulliken–Hush analysis of intervalence charge transfer (IVCT) band obtained from the spectroelectrochemical method, and (2) partial charge distribution analysis of quinonoidal distortion of D•+/D centers obtained from theoretical DFT calculations. The H12 were 2055 and 1903 cm−1 by (1) and (2), respectively. This work suggests that the pure through‐space electronic coupling can be large when two aromatic redox centers are properly aligned.