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Through-space electronic coupling in highly compressed π-stacked organic mixed-valence systems: The role of charge type and redox-center orientation
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DOI：10.1002/bkcs.70121.png)
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Abstract
En 中文
A quantitative understanding of through-space electronic coupling in pi-stacked organic mixed-valence (MV) systems remains limited, particularly in regimes where severe geometric compression and conformational effects complicate conventional spectroscopic interpretations. Here, we present a combined experimental and theoretical investigation of highly compressed pi-stacked MV systems derived from the cation-radical 3(center dot) + and the anion-radical 4(center dot) -, which possess closely comparable centroid-to-centroid separations well within the sub-van der Waals contact regime. Electrochemical and spectroscopic measurements, together with DFT and TD-DFT analyses, reveal that the lowest-energy optical transitions observed for these systems do not arise from equivalent electronic states in the cationic and anionic manifolds. In particular, the anion-radical system exhibits a pronounced conformational dependence, in which the syn conformer displays fully delocalized electronic structure consistent with Robin-Day Class III behavior, whereas the anti conformer remains Class II. As a consequence, the experimentally observed strong low-energy absorption of 4(center dot) - is dominated by the syn conformer and reflects pi-pi* excitation rather than a conventional intervalence charge-transfer process. When analyzed within a consistent computational framework, the intrinsic electronic couplings of 3(center dot) + and 4(center dot) - converge to a coherent picture in which orientation-dependent effects, rather than charge-carrier polarity alone, govern the magnitude and character of through-space electronic coupling in the highly compressed regime.
Keywords:
pi-stack
electronic coupling
mixed-valence
orientation
through-space
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