Christopher E. Bunker

Photoinduced inter- and intra-molecular electron transfer reactions of [60]fullerene and a tertiary amine. Formation of the cycloadduct N-ethyl-trans-2′,5′-dimethylpyrrolidino[3′,4′:1,2][60]fullerene

The photoreduction of [60]fullerene by triethylamine results in the formation of a cycloadduct N-ethyl-trans-2′, 5′-dimethylpyrrolidino[3′,4′: 1,2][60]fullerene, which is probably due to sequential intermolecular and intramolecular processes and argues strongly for the presence of ion pairs as intermediates in a room temperature toluene solution.

A PHOTOPHYSICAL STUDY OF SOLVATOCHROMIC PROBE 6‐PROPIONYL‐Z(N,N‐DIMETHYLAMINO)NAPHTHALENE (PRODAN) IN SOLUTION

A photophysical study of 6‐propionyl‐2‐(N,N‐dimethylamino)naphthalene (PRODAN) in room‐temperature solutions under various conditions is reported. The results show no unusual photophysical properties, except for an extremely large solvatochromic shift of PRODAN fluorescence spectrum. The previously reported extra blue emission band for PRODAN in an aqueous solution is identified to be due entirely to trace water‐soluble impurities in the sample. The excited‐state dipole moment of PRODAN is determined based on solvatochromic results using a known twisted intramolecular charge transfer (TICT) molecule p‐(N,N‐diethylamino)ethylbenzoate (DEAEB) as a reference to probe specific solute‐solvent interactions. The possibility of TICT state formation in PRODAN is discussed, and a solvation equilibrium mechanism is proposed to account for the photophysical behavior of PRODAN.

Py scale in vapor phase and in supercritical carbon dioxide. Evidence in support of a three-density-region model for solvation in supercritical fluids

Abstract With a fluorescence study of pyrene, Py (I1/I3) values are determined in the vapor phase at 70/dgC and in supercritical CO2 at 45°C over a wide density range (pr from 0.025 to 1.9.). Noise-elimination for weak pyrene vapor-phase spectra is accomplished by the application of principal component analysis. A characteristic density dependence of Py scale becomes clear with the determination of Py values at low CO2 densities, which strongly supports a three-density-region solvation model for solvent effects in supercritical fluids.

Fullerene-based macromolecules from photochemical reactions of [60]fullerene and triethylamine

Abstract [60]fullerene-triethylamine macromolecules are obtained from photoinduced electron transfer-proton transfer reactions. The material is characterized by photon correlation spectroscopy of quasi-elastic light scattering, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, NMR and FT-IR techniques. The electronic absorption and emission properties of the material are studied. Because the macromolecules likely contain intramolecular redox pairs, the possibility of intramolecular exciplexes is examined and discussed.

Effects of photochemical reactions of pyrene in alcohol and aqueous solvent systems on spectroscopic analyses

Although pyrene is a popular fluorescent molecular probe in analytical and bioanalytical chemistry, its photostability is hardly understood. This paper reports a surprising finding that pyrene undergoes significant photochemical reactions in alcohol and aqueous solvents under the condition of exposing a sample solution to excitation irradiation in an emission spectrometer for a short period of time. The reactions yield at least two photoproducts, whose fluorescence spectra overlap severely with that of pyrene. Implications of pyrene photochemical reactions in alcohol and aqueous solvent systems to existing and future applications of pyrene as a fluorescent molecular probe are discussed.

Steady-state and time-resolved fluorescence spectroscopic probing of microstructures and properties of perfluorinated polyelectrolyte membranes

A systematic luminescence spectroscopic study of the microstructures and properties of Nafion®, the Dow Chemical films, and the newly synthesized sulfonimide ionomer membrane is reported. The strongly environment-sensitive luminescent probes 6-propionyl-2-(N,N-dimethylamino)naphthalene, 4-(N,N-dimethylamino)benzonitrile, pyrene, and ethidium bromide were used. The results suggest that the different perfluorinated ionomer membranes have generally similar properties with respect to the luminescent molecular probes and that the membrane structures consist of a substantial region that may be characterized as a heterogeneous mixture of water molecules and branches of the perfluorinated polymers. In addition, the effects of thermally stressing the ionomer membranes in an aqueous solution at temperatures up to 250°C on the properties of the membranes are evaluated and discussed.

Fluorescence spectroscopic probing of two distinctive microenvironments in perfluorinated ionomer membranes

Ethidium bromide was used as fluorescent molecular probe in the understanding of structural properties of Nafion, Dow Chemical, and sulfonimide ionomer membranes. The fluorescence lifetime results show that the probe is located in the interfacial region of the membrane structure, and that the interfacial region is inhomogeneous, consisting of two distinct subsections of different hydrophilicities. The ionomer membranes under consideration have similar structural properties with respect to the ethidium cation probing, despite the fact that their corresponding ionomers have different molecular structures. The fluorescence lifetime results also show that there are considerable mobilities throughout the interfacial region, which allow diffusional quenching processes. Finally, results of effects of hydrothermally stressing Nafion membrane at elevated temperatures on structural properties of the membrane are discussed.

Photoinduced intrapolymer electron transfer in the pendant [60]fullerene-aminopolymer

Abstract A strong dependence of observed fluorescence quantum yields of fullerene chromophores in the pendant [60]fullerene-poly(ethyleneimine) on solvent polarity is reported. The solvent polarity effects of the fluorescence properties of the polymer-bound [60]fullerene cages are likely due to intrapolymer electron transfer quenching by the secondary amine units in the polymer structure.

Applications of chemometric methods to spectroscopic studies of aggregate formation and twisted intramolecular charge transfer in the gas phase and in non-polar solvents

Abstract Principal component analysis—self-modelling and non-linear least-squares spectral resolution methods were applied to quantitative fluorescence studies of the aggregate formation and the twisted intramolecular charge transfer (TICT) state emission of p-(N,N-diethylamino)ethylbenzoate (DEAEB) in the gas phase and in low-density supercritical ethane. A broad Gaussian-like fluorescence band at approximately 400 nm was obtained and assigned to the emission of DEAEB microcrystals or microsolids. It is shown that the red-shifted band can essentially be eliminated by keeping the sample undisturbed for a period of time and by selecting appropriate excitation wavelengths. The results support the conclusion that even in the gas phase the contribution of DEAEB TICT state emission is still significant. It is also demonstrated that a quantitative characterization of the excited state equilibium between the locality excited and TICT states of DEAEB in non-polar solvents can be accomplished by application of a spectral resolution method.

Ground state charge transfer complex of [84]fullerene and N,N-diethylaniline

The formation of the [84]fullerene–N,N-diethylaniline ground state charge transfer complex at different N,N-diethylaniline concentrations and temperatures has been studied by absorption spectroscopy and by use of a chemometric method principal component analysis to determine the absorption spectrum of the complex and the thermodynamic parameters of the C84 monomer–complex equilibrium.