Deprotonation Dynamics and Stokes Shift of Pyranine (HPTS)

Abstract

The short and intermediate time scale dynamics of the photoacid pyranine (1-hydroxy-3,6,8-pyrenetrisulfonic acid, commonly referred to as HPTS) are studied with visible pump-probe spectroscopy in various solvents to elucidate the nature of its proton-transfer kinetics in water. The observed time dependences of HPTS are compared with those of the methoxy derivative, MPTS. A global fitting procedure is employed to model both the spectral shift (Stokes shift) caused by solvent reorganization and deprotonation of pyranine in water. Three distinct time-dependent features can be clearly identified. They are the Stokes shift (1 ps in H 2 O and 1.5 ps in D 2 O), followed by the deprotonation processes, which gives rise to a biexponential decay of the protonated species with time constants (in H 2 O) of 3 and 88 ps. By the use of a model previously discussed in the literature, the biexponential process can be interpreted as an initial deprotonation step followed by the longer time scale process which separates the resulting ion pair. The results presented here are consistent with some of the previous reports but unambiguously identify and quantitatively measure the Stokes shift as a separate and distinct phenomenon from the deprotonation process, in contrast to other reports that have suggested that all short time (a few picoseconds) dynamics are merely a Stokes shift.

Influence of Ions on Aqueous Acid–Base Reactions

“…The response of the electronic absorption band has two contributions in the wavelength range 410 nm to 620 nm, which can be attributed to a linear combination of protonated (HPTS*) and deprotonated (PTS* À ) spectra, both of which have contributions from transient absorption and stimulated emission. The spectra agree well with the spectra reported by Spry et al [16] The timescales measured in the visible spectrum correspond well with the infrared counterpart.…”

“…[40] In this scheme, we can prepare unreactive acid-base pairs in solution and use an optical trigger to promote the HPTS molecule to an electronically excited state, thereby initiating the proton transfer reaction. HPTS has been used previously to study the dynamics of acid dissociation [9][10][11][12][14][15][16] and acid-base reactions. [17][18][19][20][21][22][23][24][25][26][27][28] The excited state of HPTS, HPTS*, deprotonates (proton transfer to solvent) with a time constant of 90 ps in H 2 O and 220 ps in D 2 O in the absence of a base.…”

Kinetics of intercalation of fluorescent probes in magnesium–aluminium layered double hydroxide within a multiscale reaction–diffusion framework

“…The electronic supplementary material, figure S13, shows the fluorescence excitation and emission spectra of the HPTS dyes during the precipitation of the LDH. The negatively charged sulfonate groups in addition to the high electron-donating ability of the hydroxyl oxygen produce a significant electrostatic interaction with the positively charged brucite-like sheets, which explains the observed blue shift [20,33]. The 27 Al SSNMR of the MgAlA LDH intercalated with HPTS reveals a peak at the δ = 72 ppm, in addition to the one present in the non-intercalated LDH (δ = 18 ppm), as shown in electronic supplementary material, figure S9.…”

“…RhB and HPTS are xanthene derivatives emitting in the red (550-650 nm) and the green (480-530 nm) regions of the visible spectrum, respectively. RhB is a three-dimensional cationic probe in an acidic medium and a neutral one (electronic supplementary material, figure S1) in a basic solution [19], while HPTS is a two-dimensional poly-anionic dye (electronic supplementary material, figure S2) having a pK a of approximately 7.3 [20]. The electronic absorption and emission spectra of these dyes, in addition to the lifetime values, are sensitive to their molecular environment [21][22][23]; thus, they are used in this paper to examine their conformation and dynamics upon intercalation in the MgAlA LDHs [24].…”

Effect of NaCl on ESPT‐Mediated FRET in a CTAC Micelle: A Femtosecond and FCS Study

“…[9][10] Ultrafast excited-state proton transfer (ESPT) has been studied in protein [human serum albumin (HSA)], [11] silicon mesoporous materials, [12] bis(2-ethylhexyl) sodium sulfosuccinate (AOT) microemulsion, [13] Nafion membrane, [14,15] and macrocyclic hosts. [16,17] Huppert and co-workers carried out a molecular dynamics (MD) simulation on ESPT of 8-hydroxypyranine-1,3,6-trisulfonate (HPTS) in a cyclodextrin cavity.…”