Browsing by Author "Ambre, Ram"

Now showing 1 - 3 of 3

Effects of Porphyrinic meso-Substituents on the Photovoltaic Performance of Dye-Sensitized Solar Cells: Number and Position of p-Carboxyphenyl and Thienyl Groups on Zinc Porphyrins
(2012-06-07)
Ambre, Ram
;
Chen, Kwan-Bo
;
Yao, Ching-Fa
;
Luo, Liyang
;
Diau, Eric Wei-Guang
In order to understand the effects of meso-substituents of the zinc porphyrins on optical, electrochemical, and photovoltaic properties, a series of porphyrins with different combinations of thienyl (S) and p-carboxyphenyl (A) groups as the meso substituents have been systematically synthesized and studied. The properties of zinc complexes 3S1A, trans-2S2A, cis-2S2A, and 1S3A were fully investigated by absorption and emission spectra, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra, density functional theory (DFT) calculations, electrochemical, photophysical, and photovoltaic measurements. With the increasing number of meso-thienyl groups, slight red-shifts of Soret and Q bands were observed in both absorption and emission spectra. All of the absorption spectra of zinc porphyrins on TiO2 film show broadening and splitting of Soret bands because of excitonic coupling of porphyrins. ATR-FTIR spectra revealed likely modes to determine either a single arm (in 3S1A and trans-2S2A) or double arms (in 1S3A and cis-2S2A) attached on TiO2. Two factors of p-carboxyphenyl and thienyl groups affecting the devices performance-heavy atom effect and the amount of dye loading on TiO2-are concluded. Overall, the power conversion efficiencies (eta) of the devices exhibit the following order: 1S3A (3.0%) > cis-2S2A (2.5%) > trans-2S2A (1.8%) >> 3S1A (0.2%).
Nickel Carbodicarbene Catalyzes Kumada Cross-Coupling of Aryl Ethers with Grignard Reagents through C-O Bond Activation
(1970-01-01)
Ambre, Ram
;
Yang, Hsuan
;
Chen, Wen-Ching
;
Yap, Glenn P. A.
;
Jurca, Titel
The development of a cross-coupling reaction protocol between aryl ethers and Grignard reagents catalyzed by carbodicarbene (CDC) nickel complexes to afford biaryl compounds through C-O cleavage is reported. Aromatic substrates featuring a broad range of electron neutral, donating, or withdrawing groups are introduced at the desired position. The method has proven effective over a wide range of naphthyl methyl ethers, anisoles, and Grignard reagents. The robustness of the protocol is validated by performing multiple cleavage reactions, gram scale synthesis, and arylation of a dimethoxy esterdiol derivative.
Nickel-mediated cross-coupling via C-O activation assisted by organoaluminum
(1970-01-01)
Liu, Cheng-Yuan
;
Wititsuwannakul, Taveechai
;
Hsieh, Chu-Han
;
Tsai, Chung-Yu
;
Wang, Ting-Hsuan
We report the alkylation and arylation cross-coupling of aryl ethers based on C-O bond activation using a nickel catalyst and organoaluminum reagents. Ni(cod)(2) in combination with 1,2-bis(dicyclohexylphosphino)ethane ligand in toluene solution at 130 degrees C are the best conditions. The naphthyl ether or methoxy pyridine derivatives are suitable substrates for alkylation and arylation reaction with a wider scope of aluminum reagents in good yields. Computational analysis on the pyridine substrate is provided to help delineate the mechanistic pathway and demonstrate the important aspects of the cooperative interaction bimetallic catalysis. First, the coordination of AlMe3 to the O atom of pyridine is essential for C-O activation. Second, the beta-H transfer from methoxy to pyridine could be discouraged through the use of bidentate phosphine as a ligand. Finally, excess AlMe3 reagent is critical for facilitating a reductive elimination process.