Shyh Gang Su

The importance of vibrational motion and solvent diffusional motion in excited state intramolecular electron transfer reactions

Time resolved emission spectroscopy has been used to examine the dynamics of intramolecular charge transfer in dimethylaminobenzonitrile (DMABN) and diethylaminobenzonitrile (DEABN) in linear alcohol solutions as a function of temperature. For both DMABN and DEABN in methanol and DMABN in ethanol solutions, the population decay of the local excited (LE) state can be fit by a single exponential function. However, over the temperature range examined, 0 to −50 °C, the population decay of the local excited state in longer chain alcohol solutions (ethanol, propanol, butanol, pentanol, and hexanol) cannot be fit by a single exponential. The average survival probability of the LE state Q(t) is obtained by fitting the population decay to a multiexponential function. In all of the alcohol solvents studied, the average lifetime of Q(t) is faster than the solvent fluctuation rate gauged by the longitudinal relaxation time of the solvent τL(τDe∞/es) corresponding to the slow collective hydrogen bonding dynamics. Comp...

Intramolecular electron transfer and solvation

The intramolecular charge transfer reaction and solvation dynamics of 4,4’‐dimethylaminophenyl sulphone in alcohols are measured using picosecond time‐resolved emission spectroscopy. The results are compared to theoretical models that treat the solvent as a dielectric continuum. In alcohol solvents, the value for τ−1L (τL =τDe∞/es) using either n2 or emw for e∞ do not provide a good gauge for the intramolecular electron transfer rate. These results are discussed in terms of the importance of vibrational contributions to the reaction rates and the applicability of the parameter τL in gauging the solvent dynamics. In addition, the time‐resolved emission data clearly show that the charge transfer state is formed out of equilibrium with the surrounding solvent structure. The measured time scales for the ensuing solvent relaxation are significantly longer than the hydrodynamic continuum model prediction of τL. The discrepancy between the observed rates and those predicted by models based on a dielectric contin...

Synthesis and Characterization of Organic Dyes Containing Various Donors and Acceptors

New organic dyes comprising carbazole, iminodibenzyl, or phenothiazine moieties, respectively, as the electron donors, and cyanoacetic acid or acrylic acid moieties as the electron acceptors/anchoring groups were synthesized and characterized. The influence of heteroatoms on carbazole, iminodibenzyl and phenothiazine donors, and cyano-substitution on the acid acceptor is evidenced by spectral, electrochemical, photovoltaic experiments, and density functional theory calculations. The phenothiazine dyes show solar-energy-to-electricity conversion efficiency (η) of 3.46–5.53%, whereas carbazole and iminodibenzyl dyes show η of 2.43% and 3.49%, respectively.

Synthesis and characterization of three organic dyes with various donors and rhodanine ring acceptor for use in dye-sensitized solar cells

A series of new organic dyes comprising carbazole, iminodibenzyl, and phenothiazine moieties as the electron donors and rhodanine ring as the electron acceptor/anchoring groups were designed and developed for use in dye-sensitized solar cells. HOMO and LUMO energy level tuning was achieved by varying the carbazole, iminodibenzyls and phenothiazine donors. This was evidenced by spectral and electrochemical experiments and density functional theory calculations. Electrochemical studies indicated that the phenothiazine unit was much more effective in lowering the ionization potential than were the iminodibenzyl and carbazole units. The phenothiazine dye shows a solar-energy-to-electricity conversion efficiency (η) of 4.87%; the carbazole and iminodibenzyl dyes show η of 2.54% and 3.52%, respectively. These findings reveal that using carbazole, iminodibenzyl and phenothiazine donors as light-harvesting sensitizers are promising candidates for dye-sensitized solar cells.

Synthesis and characterization of protic ionic liquids containing cyclic amine cations and tetrafluoroborate anion

Several ionic liquids containing pyrrolidinium-, oxopyrrolidinium-, piperidinium-, morpholinium- and trialkylammonium-based cation are synthesized and their thermal property, refractive index, polarity, electrochemical property, and temperature dependency of dynamic viscosity, density and ionic conductivity are characterized. All tetrafluoroborate-based room temperature ionic liquids studied here have a high ionic conductivity (up to 31.4 mS cm−1). These ILs were successfully used as suitable electrolytes for the diffusion coefficient measurement of ferrocene. Absorbance solvatochromic probes Nile red is used to investigate the relative polarity of these ionic liquids and compared them with several organic solvents. The relation of fluidity to conductance is considered in terms of a Walden plot that is shown to provide a useful basis for organizing the applications of solvent media for “green” synthetic reactions.

Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes

Three new organic dyes comprising carbazole, iminodibenzyl and phenothiazine moieties, as electron donors and di-anchoring rhodanine rings as the electron acceptors, were synthesized and evaluated for use in dye-sensitized solar cells. A solar cell employing dye-containing phenothiazine as a hole-transporting unit and di-anchoring rhodanine rings as the electron acceptors exhibits a short circuit photocurrent density of 10.6 mA cm-2, an open-circuit voltage of 0.658 V and a fill factor of 0.7, corresponding to an overall conversion efficiency of 4.91% at standard AM 1.5 sunlight.

Picosecond Stokes shift studies of solvent friction: Experimental measurements of time-dependent band shape and integrated intensity

Abstract The dynamic Stokes shift of the emission from a charge transfer excited state is examined in ethanol solutions over the temperature range from − 10°C to −60°C. Measurements of the time-dependent band shape and integrated intensity suggest that there is strong coupling between the electronic structure of the probe molecule and the time-dependent solvation. The time-dependent integrated intensity exhibits a biexponential decay in which the fast component is equivalent to solvation times determined from the Stokes shift correlation function, C(t). This data reflects the time-dependent contribution of the pure LE and TICT states to the excited electronic state as solvation occurs. In addition, over the temperature range studied, the time-dependent shape of the emission spectrum is found to depend solely on the motion along the solvent coordinate, suggesting that the initial decrease in integrated intensity is not the result of the presence of an inhomogeneous distribution of solvated molecules following photolysis.

Nonequilibrium and nonadiabatic effects on excited state electron transfer reactions in solution

Abstract Picosecond emission spectroscopy is used to examine the intramolecular charge transfer reaction of N,N-dimethylaminophenyl sulphone in alcohol solution. The effects of nonequilibrium distributions on the reaction surface as well as nonadiabatic effects arising from the time scale of the reactive process and solvent diffusion are discussed. The implications of these data on the motion along the reaction potential energy surface are described.

Efficient 1H-NMR quantitation and investigation of N-Acetyl-D-glucosamine (GlcNAc) and N,N'-diacetylchitobiose (GlcNAc)2 from chitin

A quantitative determination method of N-acetyl-d-glucosamine (GlcNAc) and N,N′-diacetylchitobiose (GlcNAc)2 is proposed using a proton nuclear magnetic resonance experiment. N-acetyl groups of GlcNAc and (GlcNAc)2 are chosen as target signals, and the deconvolution technique is used to determine the concentration of the corresponding compound. Compared to the HPLC method, 1H-NMR spectroscopy is simple and fast. The method can be used for the analysis of chitin hydrolyzed products with real-time analysis, and for quantifying the content of products using internal standards without calibration curves. This method can be used to quickly evaluate chitinase activity. The temperature dependence of 1H-NMR spectra (VT-NMR) is studied to monitor the chemical shift variation of acetyl peak. The acetyl groups of products are involved in intramolecular H-bonding with the OH group on anomeric sites. The rotation of the acetyl group is closely related to the intramolecular hydrogen bonding pattern, as suggested by the theoretical data (molecular modeling).

Impact of polyethyleneglycol addition on diffusion coefficients in binary ionic liquid electrolytes composed of dicationic ionic liquid and polyethyleneglycol

We conduct a comparative study of conductivity and diffusion coefficient of two dicationic ionic liquids (3,3′‐(octane‐1,8‐diyl)bis(1‐ethyl‐3‐imidazolium) bis(trifluoromethylsulfonyl)amide ([IMCI][TFSI], S1) and 3,3′‐(2,2′‐(ethane‐1,2‐diylbis(oxy))bis(ethane‐2,1‐diyl))bis(1‐ethyl‐3‐imidazolium) bis(trifluoromethylsulfonyl)amide ([IMOI][TFSI], S2)) at various temperatures. The diffusion coefficients of cation and anion in ionic liquids are determined by using pulse gradient spin‐echo nuclear magnetic resonance method. S2 shows lower viscosity, higher conductivity, and higher diffusion coefficient than those of S1. Moreover, the influence of polyethyleneglycol (PEG200, Mw = 200) addition in PEG200/IL binary solutions is investigated. PEG200/S1 binary solutions show lower viscosity, higher conductivity, and higher diffusion coefficient than those of neat S1. The experimental molar conductivity (Λ) of neat IL and PEG200/IL binary solutions is lower than that of the calculated molar conductivity (ΛNMR) from pulse gradient spin‐echo nuclear magnetic resonance method at various temperatures, indicating that not all the diffusion species belong to the ionic conduction. In other words, NMR diffusion measurements comprise charged and paired (without charge) ions. Copyright