Ferrocene donor linked to pyridine/pyridinium acceptor via a systematically enlarged π-linker

Nine chromophores with ferrocene donor and pyridine/pyridinium acceptors have been prepared and further investigated. The performed X-ray analysis showed partially polarized and geometrically oblate pyridine unit. An extension of the π-system and N-quaternization were revealed as suitable tools for exclusive manipulation of the LUMO with the almost steady HOMO. Whereas the electrochemical HOMO–LUMO gap can be tuned from 3.01 to 1.49 eV, the high- and low-energy absorption bands were found within the range of 280–402/456–547 nm. The pyridinium chromophores showed distinct negative solvatochromism. A thorough DFT analysis has been performed; it turned out that ferrocene donor is capable of two principal D–A interactions, whose employment depends on the appended electron-withdrawing moiety.


4-Iodophenylferrocene 18
4-Iodophenylferrocene was synthesized via modification literature procedure. 2 4-Iodoaniline (2.19 g, 10.0 mmol) was dissolved in a mixture of water (25 ml) and concentrated hydrochloric acid (3 ml). The resulting solution was cooled to 0 °C whereupon a solution of sodium nitrite (760 mg, 11.0 mmol) in water (50 ml) was added dropwise through a dropping funnel at a rate to keep the temperature below 5 °C. Subsequently, the reaction mixture was stirred for additional 30 min at 0 °C. A solution of ferrocene (1.86 g, 10.0 mmol) in toluene (100 ml) containing acetonitrile (3 ml) was added via a dropping funnel over a period of 15 min. After removal of the cooling bath, the reaction mixture was stirred for 12 h at 25 °C. The mixture was diluted with water (300 ml) and extracted with EtAc (3 × 100 ml). The combined organic layers were dried (Na2SO4) and the solvent was evaporated in vacuo. The crude product was purified by column chromatography (SiO2, hexane).

General method
The electrochemical behaviour of target chromophores were investigated in acetonitrile containing 0.1 M Bu4NPF6 in a three electrode cell by cyclic voltammetry (CV). The working electrode was glassy carbon disk (1 mm in diameter). As the reference and auxiliary electrodes were used leak-less Ag/AgCl electrode (SSCE) containing filling electrolyte (3.4 M KCl) and titanium rod with a thick coating of platinum, respectively. All peak potentials are given vs.

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The following localization of the frontier molecular orbitals were gained in the program OPChem. 4 Figure S20. The HOMO (red) and the LUMO (blue) localizations in chromophore 1a.
S20 Figure S25. The HOMO (red) and the LUMO (blue) localizations in chromophore 6a. Figure S26. The HOMO (red) and the LUMO (blue) localizations in chromophore 7a. Figure S27. The HOMO (red) and the LUMO (blue) localizations in chromophore 8a. Figure S28. The HOMO (red) and the LUMO (blue) localizations in chromophore 9a. Figure S29. The HOMO (red) and the LUMO (blue) localizations in chromophore 1b (the Ianion has been omitted for clarity). Figure S30. The HOMO (red) and the LUMO (blue) localizations in chromophore 2b (the Ianion has been omitted for clarity).

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S23 Figure S31. The HOMO (red) and the LUMO (blue) localizations in chromophore 3b (the Ianion has been omitted for clarity). Figure S32. The HOMO (red) and the LUMO (blue) localizations in chromophore 4b (the Ianion has been omitted for clarity).
S24 Figure S33. The HOMO (red) and the LUMO (blue) localizations in chromophore 5b (the Ianion has been omitted for clarity). Figure S34. The HOMO (red) and the LUMO (blue) localizations in chromophore 6b (the Ianion has been omitted for clarity).
S25 Figure S35. The HOMO (red) and the LUMO (blue) localizations in chromophore 7b (the Ianion has been omitted for clarity). Figure S36. The HOMO (red) and the LUMO (blue) localizations in chromophore 8b (the Ianion has been omitted for clarity).
S26 Figure S37. The HOMO (red) and the LUMO (blue) localizations in chromophore 9b (the Ianion has been omitted for clarity).