Background-Free Fluorescence-Decay-Time Sensing and Imaging of pH with Highly Photostable Diazaoxotriangulenium Dyes

Abstract

Novel fluorescent diazaoxatriangulenium (DAOTA) pH indicators for lifetime-based self-referenced pH sensing are reported. The DAOTA dyes were decorated with phenolic-receptor groups inducing fluorescence quenching via a photoinduced-electron-transfer mechanism. Electron-withdrawing chlorine substituents ensure response in the most relevant pH range (apparent pK a ′ values of ∼5 and 7.5 for the p,p-dichlorophenol- and p-chlorophenol-substituted dyes, respectively). The dyes feature long fluorescence lifetimes (17–20 ns), high quantum yields (∼60%), and high photostabilities. Planar optodes are prepared upon immobilization of the dyes into polyurethane hydrogel D4. Apart from the response in the fluorescence intensity, the optodes show pH-dependent lifetime behavior, which makes them suitable for studying 2D pH distributions with the help of fluorescence-lifetime-imaging techniques. The lifetime response is particularly pronounced for the sensors with high dye concentrations (0.5–1 wt % with respect to the polymer) and is attributed to the efficient homo-FRET mechanism.

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

“…The optical and pH responsive properties are investigated with respect to position of the phenol hydroxy group and selection of fluorophore (ADOTA or DAOTA) to find the optimal triangulenium based pH probe and test our hypothesis about high on‐off ratios in long fluorescence lifetime dyes. Fabrication of actual fluorescent sensor devices (optodes) based on structurally related phenol substituted DAOTA derivatives have very recently been reported by us and by Borisov and co‐workers focusing on materials aspects and the sensor performance rather than fundamental structure‐property relations that are the focus here.…”

“…We tentatively assign this effect to dynamic quenching of the phenol forms by the PBS buffer system. Note that this is a similar, yet much smaller effect than the strong salt effects reported by Borisov and co‐workers for optodes based of chlorophenol substituted DAOTA derivatives embedded in various polymer matrices …”

Utilizing Selective Chlorination to Synthesize New Triangulenium Dyes with Redshifted Absorption and Emission

“…[4]-and [6]-helicenes of the DMQA + type have been extensively studied. A key feature is the characteristic redshifted absorption and emission compared to 3.…”

“…[1][2][3] High chemical and photochemical stability is key to their applications in both sensors and photocatalytic processes. [4][5][6][7][8][9] Uniquely long fluorescence lifetime of the azadioxa-and diazaoxa-triangulenium dyes (ADOTA + and DAOTA + ) (τfl 20 ns) enables elimination of auto fluorescence by time-gated imaging and widens the measuring range in polarization assays. [10][11][12][13] The long fluorescence lifetime and good quantum yields (60-80%) of the ADOTA + and DAOTA + triangulenium dyes make the scaffolds obvious targets for modifications aiming at tuning the optical properties.…”

Luminescence Lifetime Imaging of O₂ with a Frequency-Domain-Based Camera System

“…The method can be used to image samples which can be put in close contact to the optode, such as certain marine animals 42 , biofilms 6 and soils 31 just to name a few. We present a standalone setup using an objective, however, the camera can easily be coupled to a microscope for higher resolution chemical imaging 43 .…”