Excited State Intramolecular Proton Transfer Reaction of 4′-N,N-Diethylamino-3-hydroxyflavone and Solvation Dynamics in Room Temperature Ionic Liquids Studied by Optical Kerr Gate Fluorescence Measurement

Abstract

Fluorescence dynamics of 4'-N,N-diethylamino-3-hydroxyflavone (DEAHF) and its methoxy derivative (DEAMF) in various room temperature ionic liquids (RTILs) have been studied mainly by an optical Kerr gate method. DEAMF showed a single band fluorescence whose peak shifted with time by the solvation dynamics. The averaged solvation time determined by the fluorescence peak shift was proportional to the viscosity of the solvent except for tetradecyltrihexylphosphonium bis(trifluoromethanesulfonyl)amide. The solvation times were consistent with reported values determined with different probe molecules. DEAHF showed dual fluorescence due to the normal and tautomer forms produced by the excited state intramolecular proton transfer (ESIPT), and the relative intensities were dependent on the time and the solvent cation or anion species. By using the information of the fluorescence spectrum of DEAMF, the fluorescence spectrum of DEAHF at each delay time after the photoexcitation was decomposed into the normal and the tautomer fluorescence components, respectively. The normal component showed a very fast decay simulated by a biexponential function (2-3 and 20-30 ps) with an additional slower decay component. The tautomer component showed a rise with the time constants corresponding to the faster decay of the normal form with an additional instantaneous rise. The faster dynamics of the normal and tautomer population changes were assigned to the ESIPT process, while the slower decay of the fluorescence was attributed to the population decay from the excited state through the radiative and nonradiative processes. The average ESIPT time was much faster than the averaged solvation time of RTILs. Basically, the ESIPT kinetics in RTILs is similar to those in conventional liquid solvents like acetonitrile (Chou et al. J. Phys. Chem. A 2005, 109, 3777). The faster ESIPT is interpreted in terms of the activation barrierless process from the Franck-Condon state before the solvation of the normal state in the electronic excited state. With the advance of the solvation in the excited state, the normal form becomes relatively more stable than the tautomer form, which makes the ESIPT become an activation process.

Medium decoupling of dynamics at temperatures ∼100 K above glass-transition temperature: A case study with (acetamide + lithium bromide/nitrate) melts

“…123 At lower temperatures where heterogeneities are longer-lived than τ r , molecular aspects get prominence and a departure from the SED description ensues. Results obtained from experimental studies of reactive and non-reactive dynamics in ionic liquids, 52,124,125 and those from very recent measurements after isothermal introduction of ∼2 nm structural inhomogeneity in an otherwise homogeneous liquid 126 suggest that both the static and dynamic heterogeneities could contribute to the observed decoupling between solute rotation and viscosity in these melts. In the absence of LiNO 3 (f LiBr = 1.0) the extent of decoupling becomes even stronger as one finds p = 0.50 at this composition (see Fig.…”

Synthesis and Structure–Property Relationships of 2,2′‐Bis(benzo[b]phosphole) and 2,2′‐Benzo[b]phosphole–Benzo[b]heterole Hybrid π Systems

“…The output (780 nm, ≈120 fs FWHM) of the optical parametric amplifier (Spectra Physics, TOPAS) excited by an amplified Ti:sapphire laser system (Spectra Physics, Spitfire XP, 800 nm, ≈120 fs FWHM) was frequency‐doubled to 390 nm by a BBO crystal, and used as an excitation pulse (for the excitation of compound 8 , the excitation pulse of 360 nm was produced). The color sensitivity and the time‐zero of the streak images were corrected as previously reported 26. Dichloromethane, acetonitrile, and benzene (spectroscopic grade) were used as received.…”

Femtosecond broadband fluorescence upconversion spectroscopy: Spectral coverage versus efficiency

“…The more accurate and precise the observation of an instantaneous emission spectrum, the more forceful will be conclusions about the underlying couplings and processes. [1][2][3] In general, if transient fluorescence band shapes are to be used in a quantitative way, then their photometric accuracy must be ensured. As a corollary, transient spectra of the same sample, but from different laboratories, should be identical.…”