Fluorescence pH Probes Based on Photoinduced Electron Transfer Quenching of Long Fluorescence Lifetime Triangulenium Dyes

Abstract

Azaoxatriangulenium dyes with long fluorescence lifetimes offer advantages in fluorescence lifetime imaging (FLIM), time‐gated detection and polarization assays. However, the long excited state lifetimes are also expected to increase sensitivity to photoinduced electron transfer (PET) quenching, potentially increasing the on‐off ratio of PET probes. We report the synthesis and investigation of the optical properties of azaoxatriangulenium salts substituted with phenol substituents for pH sensing. Two series of pH probes with the phenol hydroxy group placed in the ortho, meta, or para positions to azadioxatriangulenium (ADOTA) and diazaoxatriangulenium (DAOTA) chromophores are investigated. All the phenol‐substituted dyes possess pH‐responsive fluorescence signals in the biologically relevant pH window (pH 6–9) due to efficient intramolecular PET from the phenolate form of the pendant arm. While the PET mechanism is partly suppressed in the phenol form of the ADOTA derivatives, it is completely suppressed in the DAOTA derivatives. The long excited state lifetimes of the triangulenium dyes ensure efficient PET quenching leading to very high on‐off ratios of the pH probes. The study clearly demonstrates effects of the position of the phenol/phenolate group relative to the chromophore on both PET quenching rates and pKa values.

Evaluation of Ebselen-azadioxatriangulenium as redox-sensitive fluorescent intracellular probe and as indicator within a planar redox optode

“…In summary, we have shown that triangulenium-based dyes can be converted to redox probes by linking them to a redox sensitive motif. High photostability, long decay times and high yield synthesis are some of the arguments to further investigate triangulenium based indicators for sensor development [41,[50][51][52] as well as imaging purposes.…”

Covalent and non-covalent coupling of a Au102 nanocluster with a fluorophore: energy transfer, quenching and intracellular pH sensing

“…The PET induced quenching is observed in the presence of electron donor molecules, or by intramolecular electron transfer from electron rich functional groups, such as phenols or morpholines. 32,33 In the present case the electron transfer mechanism is most likely not the dominant quenching mechanism. Instead, the fluorescence quenching is more likely dominated by the energy transfer due to the strong spectral overlap between the KU fluorescence spectrum and the cluster absorption (Fig 1c).…”

Incorporating fluorescent nanomaterials in organically modified sol–gel materials – creating single composite optical pH sensors

“…The triangulenium based pH-sensitive DAOTA dyes, 13,69 and the sol-gel synthesis of the sensor material is reported in our previous work. 3,18,43 Previous work reports on sensors with dyes that have a triethoxysilane group in their structure, which covalently bind the dye to the silicate network of the ORMOSIL.…”