Highly photostable “super”-photoacids for ultrasensitive fluorescence spectroscopy

Abstract

The photoacid 8-hydroxypyren-1,3,6-trisulfonic acid (HPTS, pyranine) is a widely used model compound for the examination of excited state proton transfer (ESPT). We synthesized five "super"-photoacids with varying hydrophilicity and acidity on the basis of HPTS. By chemical modification of the three sulfonic acid substituents, the photoacidity is enhanced by up to more than five logarithmic units from pK*≈ 1.4 to ∼-3.9 for the most acidic compound. As a result, nearly quantitative ESPT in DMSO can be observed. The novel photoacids were characterized by steady-state and time-resolved fluorescence techniques showing distinctively red shifted spectra compared to HPTS while maintaining a high quantum yield near 90%. Photostability of the compounds was checked by fluorescence correlation spectroscopy (FCS) and was found to be adequately high for ultrasensitive fluorescence spectroscopy. The described photoacids present a valuable palette for a wide range of applications, especially when the properties of HPTS, i.e. highly charged, low photostability and only moderate excited state acidity, are limiting.

Exploring fast proton transfer events associated with lateral proton diffusion on the surface of membranes

“…A stronger photoacid is more likely to undergo ESPT. Our finding is in line with the works of Jung and coworkers (38,39), who observed an increase in the photoacid strength upon modifications of the HPTS sulfonic groups. C 12 -HPTS was tethered to the membrane (at a ratio of 1:100 probe/lipid; Materials and Methods), which was composed of the following lipids: 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-1′-rac-glycerol (POPG), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate (POPA), or 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP).…”

“…Synthesis of C 12 -HPTS Derivative. To a mixture of dodecanamine (0.5 mmol) and triethanolamine (0.5 mmol) in 10 mL of dichloromethane (0°C), 0.1 mmol of 8acetoxypyrene-1,3,6-trisulfonyl chloride (38) in 10 mL of dichloromethane was added dropwise. After warming to room temperature, the reaction mixture was stirred for another 48 h. The organic phase was washed with sodium bicarbonate and saturated sodium chloride solution before being dried over sodium sulfate.…”

Kinetic and spectroscopic responses of pH-sensitive nanoparticles: influence of the silica matrix

“…Faster uorescence uctuations, described by the second term in eqn (4), arise from the transient dark-state population. As no intensity-dependent dark-state population was noticed, which is in agreement with earlier experiments on this substance class, 64,68 the dark-state population exclusively results from the pH-dependent interconversion of the deprotonated dye (RO À form) and protonated dye (ROH form). The parameter k prot in eqn (4) describes the population of the dark-state ROH (protonation) and k deprot is the depopulation rate constant of the dark state (deprotonation).…”

“…62,63 The kinetics of ESPT, which can also be determined from the steady-state experiments, are a sensitive measurement tool for the maintenance of hydrogen-bonding networks. 64 Here, 4  was measured on an absolute PL quantum yield spectrometer (C11347, Hamamatsu) in the scan mode.…”

Spectroscopic Studies on the inclusion complex formation between 2,4-dihydroxyquinoline and cyclodextrin derivatives

“…Photoacids other than naphthol derivatives have been recently reported as highly photostable "super"-photoacids (Finkler 2014).…”