Optical limiting in the visible range: molecular engineering around N4,N4′-bis(4-methoxyphenyl)-N4,N4′-diphenyl-4,4′-diaminobiphenyl

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Abstract
We describe the synthesis and nonlinear absorption properties of triarylamine derivatives. Six molecules were synthesised by using a double Ullmann coupling procedure. UV-Vis absorption spectra show the excellent transparency of these triarylamine derivatives in the visible range (λcut-off ≤ 420 nm). Nonlinear absorption measurements show a broadband nonlinear absorption range extending between 450–650 nm with an optimised efficiency for a planar conjugated system (fluorene, molecule 10) or a hindered donor group (molecule 12). These data were interpreted by means of a two step three-photon absorption scheme: a TPA process followed by an S1→Sn ESA step; the product of both spectra is qualitatively in good agreement with nonlinear absorption spectra, leading to different molecular engineering approaches for optimisation of these features in the visible range through TPA and/or ESA properties.