UV spectroscopic studies and charge transfer properties of azobenzene-containing cyclopentadienyliron complexes of arenes: A combined experimental and density functional theoretical study

This study investigates the UV–Vis absorption and fluorescence emission of newly synthesized (η6-4-(4-nitrophenylazo) phenoxyl benzene) (η5-cyclopentadienyl) iron hexafluorophosphate (Fc-azo). Quantum chemical calculations of the orbital energy, geometrical structure, absorption spectra, and first hyperpolarizability (β) values of the Fc-azo were carried out using density functional (DFT/B3LYP and TD-DFT) methods. Comparisons between hydroxyl azobenzene compound and Fc-azo were made. Results showed that the observed spectra were in good agreement with the calculated values. The positive solvatochromism of the UV–Vis absorption of Fc-azo upon the increase in solvent polarity from the experiment and the calculated HOMO and LUMO energies showed that charge transfer occurred within the molecule. Moreover, the change in electron distribution led to the improved β for Fc-azo.

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► Cyclopentadienyliron unit is a strong electron-withdrawing group.
► Fc-azo possesses positive solvatochromic character.
► Charge transfer occurs within the molecule and leds to the improved β.