Hans-Dieter Becker

Adiabatic photochemical isomerization of cis-1-(9-anthryl)-2-phenylethylenes

Abstract The photochemical cis—trans isomerization of 1-(9-anthryl)-2-phenylethylenes (9-styrylanthracenes) has been studied by performing steady state and time-resolved fluorescence measurements. It has been found that singlet excited trans isomers are formed from their photoexcited cis precursors and this is explained in terms of an adiabatic photoreaction. Polar solvents and/or polar substituents on the styrylanthracene markedly enhance the adiabatic isomerization.

High-performance liquid chromatographic separation and detection of phenols using 2-(9-anthrylethyl) chloroformate as a fluorophoric derivatizing reagent

Abstract This paper describes the use of 2-(9-anthrylethyl) chloroformate (AEOC) as a sensitive and convenient pre-column, fluorophoric derivatizing reagent for the separation and detection of phenol (P), p-methylphenol (PMP), 3,4-dimethylphenol (DMP), and 4-tert.-butylphenol (BP) using reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection. Experiments were carried out to determine maximum fluorescence excitation and emission wavelengths, optimum derivatization pH, efficient gradient programming, calibration curves, minimum detection limits, and stabilities for AEOC-derivatized phenols. The method was applied to several industrial waste water samples from Central Pennsylvania. The minimum detection limits for injected phenol samples ranged from 7 to 10 nM, or 9, 10, 12 and 11 pg for P, PMP, DMP and BP, respectively. This corresponded to concetrations of phenols in the original waste water samples of 56 to 80 nM.

Dienophilic anthracenes: formation of novel triptycenes via thermal and photochemical intramolecular diels-alder reactions of dianthrylethanes

Abstract 1,2-Di(9-anthryl) ethanes, accessible by thermolysis of lepidopterenes, undergo thermal and photochemical intramolecular Diels-Alder reactions to give 1,2-dihydroanthracenes whose aromatization leads to novel derivatives of triptycene.

On the relationship between fluorescence and molecular geometry. Formation of a luminescent intramolecular anthracene-ethylene exciplex by electronic excitation of lepidopterene

Abstract Electronic excitation of the bridged benzenoid hydrocarbon lepidoptene (L) in the crystalline state and in solution gives rise to an anomalous luminescence which is attributed to the radiative deactivation of an intramolecular anthraceneethylene exciplex E*. The formation of E* and the regeneration of L are discussed in terms of a geometry-dependent reversible [4 + 2] cycloaddition. Relevant quantum yield data are presented in an energy level diagram.

Automated amino acid determination by high-performance liquid chromatography with 2-(9-anthryl)ethyl chloroformate as precolumn reagent

Abstract A fully automated HPLC method for the determination of amino acids in protein hydrolysates has been developed, using 2-(9-anthryl)ethyl chloroformate and precolumn derivatization. This UV sensitive reagent reacts rapidly with both primary and secondary amines at room temperature to form stable carbamate derivatives. The reaction conditions have been thoroughly investigated. A complete separation of protein hydrolysates is accomplished within 40 min. The results are compared to those of the well known 9-fluorenylmethyl chloroformate method. Detection limits for UV and fluorescence detection were found to be 0.5 pmol and 0.06 pmol, respectively.

Formation and photochemical rearrangement of carbon-oxygen-linked anthracenes

Abstract Alkyl esters of 9-anthrilic acid isomerize both thermally and photochemically by stereoselective Diels-Alder reaction, while treatment with base induces the shift of 9-anthryl from carbon to oxygen. Photoexcitation of carbon-oxygen-linked bichromophoric anthracenes results in a migratory 9-anthryloxy - 9-anthronyl rearrangement.

High-performance liquid chromatographic separation of biogenic polyamines using 2-(1-pyrenyl)ethyl chloroformate as a new fluorogenic derivatizing reagent

The application of a new fluorogenic pre-column derivatizing reagent, 2-(1-pyrenyl)ethyl chloroformate (PEOC), is reported for the separation and detection of biogenic polyamines using column liquid chromatography. The development of the method included the optimization of excitation and emission wavelengths, efficient gradient programming, derivatization temperature, time, and pH. Minimum detection limits, linear ranges, reproducibility, and recovery from analyzed samples were determined. The procedure was applied to hydrolyzed serum samples taken from healthy individuals and cancer patients. Separation of PEOC-derivatized polyamines from the serum hydrolysis by-products was successful and detection limits were more favorable than those previously reported for 9-fluorenyl-methyl chloroformate-derivatized polyamines.

Adiabatic photoreactions involving anthracenes. Intramolecular exciplex formation by photolytic cycloreversion

Abstract The adiabatic photolytic cycloreversion of substituted lepidopterenes L into their retro-Diels-Alder products of exciplex geometry E ∗ has been studied by emission spectroscopy. Evidence for excited-state isomerization of cycloreversion products is presented. Fast radiationless deactivation of L ∗ is observed in chlorolepidopterenes. For bichromophoric α-naphthylmethyl- and β-styryl-substituted lepidopterenes, intramolecular energy transfer from L ∗ to the substituent competes with adiabatic photolytic cycloreversion.

Photochemical dimerization modes of 1-acetylanthracene and methyl 1-anthracenecarboxylate

Abstract Irradiation of 1-acetylanthracene in dichloromethane at light wavelengths above 400 nm gives five dimers in a ratio of about 2:1:1:1:1. In addition to the four typical modes of dimerization leading to symmetrical dianthracenes of anti -head-to-tail, syn -head-to-tail, anti -head-to-head and syn -head-to-head structures, 1-acetylanthracene undergoes dissymmetrical head-to-tail 4 π +4 π cyclodimerization involving the 1,4 and 9′,10′ positions. Selective photoexcitation of 1-acetylanthracene in the presence of anthracene gives the mixed 9,10−9′,10′ and 1,4−9′,10′ 4 π +4 π cycloadducts in a ratio of about 3:1. The photochemical dimerization of methyl 1-anthracenecarboxylate proceeds in the same fashion as that of 1-acetylanthracene.

Intramolecular deactivation of photoexcited anthracenes by aromatic ketones

Abstract The excited state properties of anthracenes non-conjugatively linked to various types of aromatic ketone were investigated in non-polar solution by determination of the quantum yields of fluorescence and intersystem crossing. In a series of substituted bichromophoric ω-(9-anthryl)propiophenones, the degree of intramolecular fluorescence quenching by the ketone was found to be associated with an increase in the quantum yield of anthracene triplet state formation. Excitation of 4′-piperazinoacetophenone tethered to anthracene resulted in deactivation within the acetophenone chromophore, rather than singlet energy transfer to anthracene. For photoexcited anthracene linked to 2-amido-substituted fluorenone, intramolecular exothermic transfer of the singlet excitation energy to the fluorenone chromophore was found to proceed with high efficiency.