Sheryl A. Tucker

Intrinsic Fluorescence of Carboxylate-Terminated Polyamido Amine Dendrimers

The “intrinsic” fluorescence of carboxylate-terminated polyamido amine (PAMAM-CT) dendrimers is studied by two fluorescence techniques—excitation-emission matrices (EEMs) and lifetimes. The EEMs show similar spectral profiles for all dendrimer generations (a broad peak with an excitation and emission maximum of 380 and 440 nm, respectively) and an overall increase in relative fluorescence emission with increasing generation. Three distinct, fairly discrete lifetimes are also recovered. The shortest lifetime (0.2–0.4 ns) is a background signal from the solvent. The two longer lifetimes (1.3–2.5 and 4.2–7.1 ns) are attributed to the dendrimer. There is a general shift to longer lifetimes in τ2 and τ3, with increasing generation (Gn). Both lifetimes nearly double in magnitude, going from G2.5 to G7.5, which is indicative of a specific fluorescent component being in a more protected or constrained microenvironment. These results imply that the dendrimer becomes densely packed with increasing generation. The weak, but detectable, fluorescence is most likely due to an n → π transition from the amido groups throughout the dendritic structure. Even though the exact nature of PAMAM-CT fluorescence is not fully understood, it is clear that this property shows the unique aspects of the architecture of these dendrimers and can be utilized in their characterization.

Spectroscopic Properties of Polycyclic Aromatic Hydrocarbons: Effect of Solvent Polarity on the Fluorescence Emission Behavior of Select Fluoranthene, Fluorenochrysene, Indenochrysene, and Indenopyrene Derivatives

Fluorescence emission behavior is reported for benz[def]indeno-[1,2,3hi]chrysene, fluoreno[2,3,4,9defg]chrysene, benz[def]indeno-[l,2,3qr]chrysene, dibenzo[a,e]fluoranthene, indeno[1,2,3cd]pyrene, naphtho[1,2b]fluoranthene, benzo[b]fluoranthene, fluoranthene, benzo-[ghi]fluoranthene, naphtho[2,1a]fluoranthene, naphtho[2,3b]fiuoranthene, benzo[k]fluoranthene, and benzo[j]fluoranthene dissolved in organic nonelectrolyte solvents of varying polarity. Results of these measurements are used to classify the various solutes as either probe or nonprobe molecules, depending upon whether measured emission intensity ratios vary systematically with solvent polarity. Also discussed are primary and secondary inner-filtering artifacts associated with selective quenching agents used to help identify/analyze polycyclic aromatic hydrocarbons (PAHs) in unknown mixtures. Inner-filtering artifacts are illustrated by examining fluorescence emission intensities of 13 “nonalternant” PAHs at different nitromethane concentrations and solution absorbances.

Fluorescence Emission Properties of Polycyclic Aromatic Compounds in Review

Abstract Fluorescence emission behavior of polycyclic aromatic hydrocarbons (PAHs), polycyclic aromatic nitrogen heterocycles (PANHs), polycyclic aromatic sulfur heterocycles (PASHs) and benzofluoranthenes dissolved in organic solvents of varying polarity is reviewed. Measured fluorescence properties are used to divide aromatic solutes into two categories, probe and nonprobe molecules, depending upon whether the molecules emission intensity ratios vary systematically with solvent polarity. Seventeen polycyclic aromatic hydrocarbon solute probes are identified and possible probe character versus molecular structure correlations are examined. Also discussed are instrumental and chemical artifacts associated with accurate determination of fluorescence emission intensities.

Spectroscopic Investigation of Fluorescence Quenching Agents: Effect of Nitromethane on the Fluorescence Emission Behavior of Select Cyclopenta-PAH, Aceanthrylene, and Fluorene Derivatives

Nitromethane is examined as a selective fluorescence quenching agent for “alternant” alkyl-substituted polycyclic aromatic hydrocarbons (PAHs). Fluorescence emission behavior is reported for 11H-benz[bc]aceanthrylene, 4H-cyclopenta[def]phenanthrene, 4H-cyclopenta[def]chrysene, 13H-dibenzo[a,g]fluorene, 13H-dibenzo[a,i]fluorene, 4H-benzo[b]cyclopenta[mno]chrysene, 4H-cyclopenta[pqr]picene, 7H-dibenzo[c,g]fluorene, 9H-benz(6,7)indeno[1,21]phenanthrene, 4H-benzo[b]cyclopenta[jkl]triphenylene, 13H-dibenz[bc,k]aceanthrylene, 13H-dibenz[bc,l]aceanthrylene, and 4H-benzo[def]cyclopenta[mno]chrysene dissolved in organic solvents of varying polarity and in acetonitrile or aqueous-acetonitrile solvent mixtures at various nitromethane concentrations. Results of these measurements show that nitromethane quenches fluorescence emission of the thirteen solutes studied, which is in complete agreement with what would be expected on the basis of the fact that all solutes are “alternant” polycyclic aromatic hydrocarbons.

Thermochemical investigations of hydrogen-bonded solutions: development of a predictive equation for the solubility of anthracene in binary hydrocarbon

Abstract Acree W.E., Jr., Zvaigzne A.I. and Tucker S.A., 1994. Thermochemical investigations of hydrogen-bonded solutions: development of a predictive equation for the solubility of anthracene in binary hydrocarbon + alcohol mixtures based upon Mobile Order theory. Fluid Phase Equilibria, 92: 233-253. Experimental solubilities are reported for anthracene dissolved in twelve binary solvent mixtures containing either 2-propanol or 1-octanol with n -hexane, n -heptane, n -octane, cyclohexane, methylcyclohexane and 2,2,4-trimethylpentane at 25.0°C. Results of these measurements, along with previously published solubility data for anthracene in binary 1-propanol+alkane and 1-butanol + alkane mixtures, are used to test the limitations and applications of expressions derived from Mobile Order theory. The best descriptive equation expresses the logarithm of the volume fraction solubility in binary mixtures as a simple volume fraction average of the corresponding logarithm solubilities in the two pure solvents, and contains additional terms to represent contributions from nonspecific physical interactions between dissimilar solvent components, from molecular size disparity, and from the reduction in mobile disorder caused by the self-association by hydrogen bonding of the alcohol solvent. The newly derived expression predicts the observed anthracene solubilities to within an overall average deviation of ca. 4.4% using a single value of K c = 5000 for the self-association equilibrium constant.

Polycyclic Aromatic Hydrocarbon Solute Probes. Part VI: Effect of Dissolved Oxygen and Halogenated Solvents on the Emission Spectra of Select Probe Molecules

Fluorescence emission properties of pyrene, benzo[ghi]perylene, coronene, and ovalene dissolved in carbon tetrachloride, chloroform, and dichloromethane are reported. Measurements indicate that the emission intensities of select solutes are time dependent, and suggest that the polycyclic aromatic hydrocarbon molecule undergoes a photochemical reaction with the chlorinated solvent. The effect of dissolved oxygen on the experimental ratio of emission intensities is also reported.

Polycyclic Aromatic Hydrocarbon Solute Probes. Part VII: Evaluation of Additional Coronene Derivatives as Possible Solvent Polarity Probe Molecules

Fluorescence emission spectra are reported for dinaphtho[8,1,2abc; 2′,1′,8′klm]coronene, naphtho[8,1,2abc]coronene, naphth[2′,1′,8′,7′: 4,10,5]anthra[1,9,8abcd]coronene, dibenzo[bc,ef]coronene, benzo[1,2,3bc;4,5,6b′c′]dicoronene, anthra[2,3a]coronene, dinaphtho-[8,1,2abc;2′,1′,8′jkl]Coronene, and tetrabenzo[de,hi,mn,qr]naphthacene dissolved in n-hexadecane, butyl acetate, dichloromethane, and acetonitrile. Results of these measurements are used to screen PAHs for potential solvent polarity probe behavior. Of the eight PAHs studied, only naphtho[8,1,2abc]coronene, dinaphtho[8,1,2abc;2′,1′,8′klm]-coronene, and anthra[2,3a]coronene were classified as probe molecules. The fluorescence spectra of the first two PAHs show selective enhancement of the I band emission intensity in polar solvents. For anthra-[2,3a]coronene, the measured ratio of emission intensities of bands I and II decreased systematically with increasing solvent polarity.

Spectroscopic Properties of Polycyclic Aromatic Compounds

Abstract Fluorescence emission spectra have been measured for acenaphthylene, aceanthrylene, acephenanthrylene, benz[ e ]aceanthrylene, 3-methylbenz[ j ]aceanthrylene, 6-methylbenz[ j ]aceanthrylene, benzo[ def ]cyclopenta[ hi ]chrysene, cyclopenta[ cd ]pyrene (also called acepyrylene) and acenaphth[1,2 a ]acenaphthylene in organic nonelectrolyte solvents of varying polarity. Benz[ e ]aceanthrylene was found to exhibit probe character for many of the solvents considered; however, emission intensity ratios in benzene, toluene, p -xylene and o -xylene were too small compared against nonelectrolyte solvents of similar polarity. The effect of nitromethane as selective quenching agent was also examined. Results of these measurements show that nitromethane does quench the fluorescence emission of the nine solutes studied, which is contrary to what would be expected based upon the fact that all nine solutes are nonalternant polycyclic aromatic hydrocarbons.

Polycyclic Aromatic Hydrocarbons and Polycyclic Aromatic Sulfur Heterocycles: Examination of Molecular Structure- Fluorescence Probe Character Correlations

Fluorescence emission spectra are reported for 1,6-dithiapyrene, 3,10-dithiaperylene, 1,7-dithiaperylene, thianthrene, benz[4,10]anthra-[1,9,8abcd]coronene, and benzo[cd]chryseno [4,5,6,7fghijk] perylene dissolved in several nonelectrolyte solvents of varying polarity. Emission spectra of the four polycyclic aromatic sulfur heterocycles (PASHs) contained very little fine structure. Severe spectral distortion, along with significant band broadening, was often observed in the case of PASHs dissolved in polar solvents. Benz[4,10]anthra[1,9,8abcd]coronene showed some probe-like character as evidenced by selective emission intensity enhancement of band I in dimethyl sulfoxide as compared to n-hexadecane solvent. The ratio of emission intensities for benz[4,10]anthra-(1,9,8abcd]coronene, however, failed to vary systematically with solvent polarity. Results of these fluorescence measurements indicate that all six solutes are unsuitable for solvent polarity probes.

Spectroscopic Properties of Polycyclic Aromatic Compounds. Part IV: Effect of Solvent Polarity and Nitromethane on the Fluorescence Emission Behavior of Select Bipolycyclic Aromatic Hydrocarbons

Fluorescence emission behavior is reported for 1,1′-binaphthalene, 2,2′-binaphthalene, 9,9′-bianthracene, 9,9′-biphenanthrene, 1,1′-methylene-bisnaphthalene, and 1,1′,2,2′-tetrahydro-5,5′-biacenaphthylene dissolved in organic nonelectrolyte solvents of varying polarity, refractive index, and dielectric constant. Fluorescence measurements are used to classify the six bipolycyclic aromatic hydrocarbon (bi-PAH) solutes as either solvatochromic probe or nonprobe molecules, depending upon whether measured fluorescence properties vary with solvent nature. Of the bi-PAHs studied, only 9,9′-bianthracene exhibited probe character. Possible correlations between 9,9′-bianthracenes maximum intensity emission wavelength and select functions of solvent refractive index and dielectric constant were examined. Also reported is the effect that nitromethane has on bi-PAH fluorescence emission intensities.