Tris(4?-Nitrobiphenyl)amine-An Octupolar Chromophore with High Two-Photon Absorption Cross-Section and Its Application for Uncaging of Calcium Ions in the Near-Infrared Region

Compounds with high two-photon absorption (2PA) performance in the near-infrared region have attracted great attention because of their application in the material and biological science. In this study, we have developed a simple and novel octupolar chromophore, tris(4 '-nitrobiphenyl)amine 1, with three nitro peripheral groups attached to a triphenylamine core via biphenyl linkers. A mono-branched analogue 2 has also been prepared to investigate the effects of octupolar and dipolar systems on photophysical and 2PA behaviors. Compound 1, despite having a much simpler structure than the previous three-branched scaffolds, exhibits comparable sigma 2 values, reaching 1330 GM at 730 nm and 900 GM at 820 nm in toluene. Combined with an outstanding sigma 2/MW ratio (2.2 GM g-1 mol) and a high fluorescence quantum yield (0.51), 1 displays potential as a promising two-photon (2P) probe for bioimaging. Subsequently, the ethylene glycol tetraacetic acid-substituted derivatives featuring octupolar (3 and 5) or dipolar (4 and 6) character have been synthesized and their one-photon (1P) and 2P photochemical reactions have been examined. Finally, 1P-and 2P-triggered uncaging of Ca2+ from these calcium chelators has been confirmed.

Automated summary

This study developed a simple and novel octupolar chromophore with potential as a two-photon probe for bioimaging. The compound exhibited comparable two-photon absorption performance to previous compounds. Additionally, ethylene glycol tetraacetic acid-substituted derivatives with octupolar or dipolar characteristics were synthesized and their ability to release calcium ions under one-photon and two-photon excitation was confirmed.