title: Two-photon polarity probes built from octupolar fluorophores: synthesis, structure-properties relationships, and use in cellular imaging.
abstract: A series of octupolar fluorophores built from a triphenylamine (TPA) core connected to electron-withdrawing (EW) peripheral groups through conjugated spacers has been synthesized. Their photoluminescence, solvatochromism, and two-photon absorption (2PA) properties were systematically investigated to derive structure-property relationships. All derivatives exhibit two 2PA bands in the 700-1000 nm region: a first band at low energy correlated with a core-to-periphery intramolecular charge transfer that leads to an intense 1PA in the blue-visible range, and a second more intense band at higher energy due to an efficient coupling of the branches through the TPA core. Increasing the strength of the EW end groups or the length of the conjugated spacers and replacing triple-bond linkers with double bonds induces both enhancement and broadening of the 2PA responses, thereby leading to cross-sections up to 2100 GM at peak and higher than 1000 GM over the whole 700-900 nm range. All derivatives exhibit intense photoluminescence (PL) in low- to medium-polarity environments (with quantum yields in the 0.5-0.9 range) and display a strong positive solvatochromic behavior (with Lippert-Mataga specific shifts ranging from 15,000 to 27,500 cm(-1)), triple bonds, and phenyl moieties in the conjugated spacers, thereby leading to larger sensitivities than those of double bonds and thienyl moieties. More hydrophilic derivatives were also shown to be biocompatible, to retain their 2PA and PL properties in biological conditions, and finally to be suitable as polarity sensors for multiphoton cell imaging.
authors.affiliation: Chimie et Photonique Moléculaires, CNRS UMR 6510, Université de Rennes 1, Campus de Beaulieu, F-35042 Rennes Cedex (France).
authors.forename: Céline
authors.initials: C
authors.lastname: Le Droumaguet
authors.forename: Aude
authors.initials: A
authors.lastname: Sourdon
authors.forename: Emilie
authors.initials: E
authors.lastname: Genin
authors.forename: Olivier
authors.initials: O
authors.lastname: Mongin
authors.forename: Mireille
authors.initials: M
authors.lastname: Blanchard-Desce
mesh_terms: D000814:Aniline Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D057809:HEK293 Cells; D006801:Humans; D008856:Microscopy, Fluorescence; D015394:Molecular Structure; D017785:Photons; D013329:Structure-Activity Relationship
chemical_list: D000814:Aniline Compounds; D005456:Fluorescent Dyes
keywords: absorption; bioimaging; chromophores; fluorescence; solvatochromism