Ming-Li Peng

Facile Preparation of 3,4-Diarylpyrroles and Hydrogen by a Platinum(II) Terpyridyl Complex

With visible-light irradiation of the platinum(II) terpyridyl complex 1 (lambda > 450 nm), an effective photocatalytic conversion from readily available 3,4-diaryl-2,5-dihydropyrroles (2a-2e) to 3,4-diarylpyrroles (3a-3e) and hydrogen (H(2)) is achieved with high efficiency and large catalytic turnover in a homogeneous solution.

Switch between charge transfer and local excited states in 4-aminophenyl-substituted Hantzsch 1,4-dihydropyridine induced by pH change and transition metal ions

The absorption and fluorescence spectra of a Hantzsch 1,4-dihydropyridine derivative bearing a N,N-dimethylaminophenyl group at 4-position (H(2)Py-PhN(CH(3))(2)) in aprotic solvents have been examined and compared to model compounds 4-phenyl- and 4-methyl-substituted Hantzsch 1,4-dihydropyridines (H(2)Py-Ph and H(2)Py-Me). While H(2)Py-Ph and H(2)Py-Me show fluorescence around 420 nm from the local excited state of the dihydropyridine chromophore, H(2)Py-PhN(CH(3))(2) exhibits fluorescence around 520 nm from the intramolecular charge transfer (ICT) state involving the aniline and dihydropyridine groups as donor and acceptor, respectively. Upon addition of an acid to the solution of H(2)Py-PhN(CH(3))(2), the amino group in the aniline is protonated. Thus, the photoinduced intramolecular charge transfer is prevented, and only the fluorescence from the local excited state of the dihydropyridine chromophore can be detected. These changes in the fluorescence behavior are fully reversible: subsequent addition of a base to the acidic solution leads to the recovery of the ICT fluorescence and the quenching of the local fluorescence. Transition metal ions also can switch the fluorescence of H(2)Py-PhN(CH(3))(2). Evidence for the interaction between transition metal ions and the amino group in the dimethylaniline have been provided by absorption and emission spectrum as well as NMR studies.

A comparative study on photosensitized oxidation of trans-2-vinylthiophenes with trans-3-vinylthiophenes

The photosensitized oxidation of trans-2-styrylthiophenes (trans-2-ST), trans-3-styrylthiophenes (trans-3-ST) and trans-1,2-di(2-thienyl)ethylene (trans-2-TE) were investigated using the sensitizers tetraphenylporphyrin (TPP) in a non-polar solvent and 9,10-dicyanoanthracene (DCA) in a polar solvent. The oxidation pathway is dependent on the position of the vinyl substituent in the thiophene ring. While trans-2-ST and trans-2-TE only undergo photooxidation via the singlet oxygen pathway to yield [4+2] and [2+2] products, the photosensitized oxidation of trans-3-ST proceeds exclusively via the superoxide anion pathway to produce the thiophenecarboxaldehyde and benzaldehydes. All of the above substrates may undergo auto-photooxidation via a charge-transfer complex of the substrate and oxygen.