Influence of electron-withdrawing groups in two-photon absorption of imidazopyridines derivatives

• Published in: Dyes and pigments Vol. 198; p. 109972
• Main Authors: Pelosi, André Gasparotto, Zucolotto Cocca, Leandro Henrique, Abegão, Luis M.G., Sciuti, Lucas Fiocco, Piguel, Sandrine, De Boni, Leonardo, Mendonça, Cleber R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2022; Elsevier
• Subjects: Chemical Sciences; Electron-withdrawing groups; imidazo[4,5-b]pyridines; SOS model; Two-photon absorption; Ultrafast transient absorption; Electron-withdrawing groups; SOS model; Two-photon absorption; imidazo[4,5-b]pyridines; Ultrafast transient absorption
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/j.dyepig.2021.109972

This work investigates the influence of different electron-withdrawing groups (Cl, Br, fluorobenzonitrile), on the two-photon absorption cross-section of six imidazo[4,5-b]pyridine derivatives. The two-photon absorption cross-section spectra were obtained by ultra-fast Z-scan technique from 470 nm up to 700 nm. The Sum-Over-States approach was applied to model the two-photon absorption spectra, using a three-level energy system. Photophysical properties, such as transition dipole moment, the difference of permanent dipole moments, and anisotropy coefficient were determined through the analysis of one-photon absorption spectra, solvatochromism, and fluorescence anisotropy, respectively. Besides, the excited state absorption spectra were measured through ultra-fast transient absorption, allowing the excited state lifetime and spectral position determination. Two-photon absorption cross-sections of about 160 GM were observed when two electron-withdrawing groups are linked to the imidazo[4,5-b]pyridine core, elucidating a path to achieve high optical nonlinearities in imidazopyridine derivatives. Furthermore, a increase in the two-photon cross-section was observed when chloride is linked at the C-6 position (90 GM) instead of the C-5 position (50 GM), which is related to the proximity of a higher excited state. •Evidence of contribution of excited states on two-photon absorption of imidazo[4,5-b]pyridines.•Study of the two-photon absorption spectrum in analog bases.•High two-photon absorption cross section (160 GM) of imidazo[4,5-b]pyridines with two electron-withdrawing groups.•Two-photon absorption modeled by using sum-over-states apporach.•Ultrafast transient absorption of imidazo[4,5-b]pyridines revealing an excited state at 560 nm.