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Imidazole-Centered Tripodal Chromophores: Synthesis, Optical Properties, and Two-Photon Absorption

Authors: Kulhánek Jiří | Bureš Filip | Burešová Zuzana | Fakis Mihalis | Klikar Milan

Year: 2025

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
eng	Imidazole-Centered Tripodal Chromophores: Synthesis, Optical Properties, and Two-Photon Absorption	Linear (D–π–A), quadrupolar ((D–π)₂–A/(A–π)₂–D), and tripodal ((D–π)₃–A/(A–π)₃–D) push–pull chromophores continue to attract attention due to their unique properties, predominantly governed by the extent of intramolecular charge transfer (ICT) from the donor (D) to the acceptor (A). Tripodal push–pull chromophores with a D–(π–A)₃ arrangement were synthesized using 1-methyl-2,4,5-triphenyl-1H-imidazole as a central electron donor. Their thermal, electrochemical, photophysical, and nonlinear optical properties were thoroughly investigated and supported by quantum-chemical calculations. Knoevenagel reactions enabled incorporation of various peripheral electron acceptors such as malonic/acetic acid derivatives, indan-1,3-dione, and rhodamine (Figure 1). All phenyl rings attached to the central imidazole core exhibited a varying degree of twisting depending on the nature of the appended peripheral substituents. While imidazole undergoes reversible one-electron oxidation, the peripheral acceptors are reduced irreversibly in a multi-electron process. This behavior is reflected in variation of the LUMO energy levels, whereas the HOMO remained relatively constant throughout the series. DFT calculations revealed centrifugal charge transfer from the central imidazole to all C2, C4, and C5 branches occupied by the LUMO and LUMO+1. The HOMO–LUMO gap is tunable within the range of 2.56 to 2.31 eV, while the longest-wavelength absorption and emission maxima were found within a broad range of 393 to 612 nm. Although the absorption spectra were solvent-independent, the emission strongly depend on the solvent polarity and the electron-withdrawing strength of the peripheral acceptors. The investigated chromophores exhibited relatively strong and tunable two-photon absorption, with δ₂PA values ranging from 286 to 521 GM.	push–pull chromophores; Knoevenagel reaction; two-photon absorption