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We have designed tripyridine-thiolato (4, 4 ′ , 4 ″ -tricarboxy-2, 2 ′ : 6 ′ , 2 ″ -terpyridine)ruthenium(II) [complex 1], a novel efficient sensitizing dye for dye sensitized TiO 2 solar cells, based on the DFT MO calculations with PBE0 functional. Complex 1 is a modified BD (black dye: trithiocyanato (4, 4 ′ , 4 ″ -tricarboxy-2, 2 ′ : 6 ′ , 2 ″ -terpyridine)ruthenium(II) complex) molecule where NCS ligands of BD are replaced by C 5 H 4 NS ligands. Molecular and electronic structures of complex 1 have been theoretically characterized. Complex 1 is expected to have the following two advantages over BD, in addition to the advantage of high electron transfer rate from the photoexcited dye to TiO 2 realized in BD: (1) higher electron transfer rate from redox systems to oxidized dyes; (2) higher absorption efficiency to solar spectrum. We propose complex 1 as a novel efficient sensitizing dye which provides the higher efficiency than does BD for dye sensitized solar cells.

One of the most efficient sensitizing dye called black dye for the dye-sensitized nanocrystalline TiO 2 solar cells have been investigated by the density functional theory study. The microscopic mechanism of electron injection into TiO 2 through the excited state(s) of the dye and electron acceptance from the redox system such as iodide by the oxidized dye molecule has been proposed. The excited electron, which is localized on the terpyridine ligand, can be efficiently injected into TiO 2 . The generated hole, which is localized on the S atom of NCS ligand, can be efficiently filled with the electron from the redox systems. These are the key reason why the sensitization of the black dye is remarkably efficient.

Polysilane oligomer radical anions with up to six Si atoms have been theoretically investigated as model molecules of high polymer polysilane radical anions by ab initio MO theory. According to the calculated results, the polysilane oligomer radical anions can exist as bound anions having a σ-type ground state with an unpaired electron occupying a Si−Si antibonding σ* orbital. They are stabilized with an increase in the Si−Si main chain length both in terms of the boundness of an unpaired electron and bonding strength. The π-type states, on the other hand, exist as excited states for these oligomer radical anions. The calculated results strongly suggest that polysilane radical anions with a π-type ground state are hardly generated regardless of their molecular size and geometry. The Si 3d orbital contributions in the ground and excited states of the polysilane radical anions, such as dπ−dπ conjugations, have also been investigated.

The hydroxylation mechanism of the H-terminated Si surface in aqueous solutions has been theoretically studied by a quantum chemical approach. OH − ion instead of H 2 O plays a dominant role in the surface hydroxylation, where two different reaction pathways exist. One of them is accompanied with the SiSi back bond cleavage. The high reactivity of the residual surface SiF bonds is also discussed.

The potential energy surface of the vinyl chloride radical anion, which is the simplest chlorine-containing hydrocarbon anion having a CC π system, has been studied by ab initio molecular orbital theory. The calculated results indicate that the initial 2 Π state is rapidly changed to the repulsive 2 Σ state by a CCl out-of-plane deformation during CCl dissociation. While no metastable 2 Π state is found on the potential energy surface, the same kind of planar metastable weak complex is found on the minimum energy path as in the case of the methyl chloride radical anion. The differences and similarities between the CCl dissociation minimum energy paths of the vinyl chloride and methyl chloride radical anions are also discussed.

Quantum chemical calculation is applied to investigate the reaction mechanism of sulfonyl acid generator and the transparency of the resist material. We have found that electron absorbed dimethylsulfone can be easily decomposed by relatively low energy (2.95Kcal/mol), reaching to the decomposed status of methyl radical and CH3SO2 (methyl sulfonyl anion). This was thought to bean initial step in the electron acid generation reaction of the sulfonyl compounds. The total molecular energy of dimethyl sulfone anion was found to be higher than that of the neutral dimethylsulfone. On the other hand, sulfone derivatives with electron-withdrawing groups, such as methyl sulfonyl acetonitrile, usually have higher energy (about 41kcal/mol) than those for their anion. This suggests that the electron withdrawing groups enhance the electron affinity of the sulfone compounds, which are also considered to increase the efficiency of acid generation. Additionally, another quantum chemical study was carried out in order to improve transparency of the aromatic species in resist for ArF excimer laser. Using configuration interaction (CI) methods of molecular orbital theory, the substituent effects of UV absorption in the aromatic compounds were investigated. As a result significant red sifts in λmax were observed in the conjugated romatic rings, which increases the transparency at 193nm wavelength region.

The reaction of trimethylaluminium (Al(CH 3 ) 3 , TMA) with H 2 has been investigated using ab initio molecular orbital calculations. It has been shown that the activation energy of the reaction, TMA + H 2 → AlH(CH 3 ) 2 + CH 4 , is about 1/2 of the dissociation energy of radical decomposition, TMA → Al(CH 3 ) 2 + CH 3 . This means that TMA decomposition under conditions where collisions between TMA and H 2 are sufficiently frequent is dominated by hydrogenolysis. This explains the experimental result that the decomposition temperature of TMA becomes lower with increasing H 2 pressure.

Disilane, silylgermane, and digermane radical anions have been studied by ab initio molecular orbital theory, using the unified level of basis set as prototypes of polymer anions with Si and Ge backbones. These prototype anions have the same kind of minimium geometry (C 2h or C 2h -like symmetry) with an unpaired electron occupying the Si-Si, Si-Ge, or Ge-Ge σ * antibonding orbital with a large Si or Ge s diffuse orbital contribution. Littke Si 3d or Ge 4d orbital participation is found for these anions

Substituent effects on the silane radical anion have been studied by ab initio molecular orbital theory. According to the calculated results, the second-row substituents tend to stabilize the silane anion more than do the first-row substituents. It has also been found that the stability of an unpaired electron is increased with an increase in the electron-withdrawing effect of the substituents, at least as far as the same-row substituents are concerned. The difference between the first- and second-row substituent effects can be qualitatively explained both by the orbital interaction based on perturbation theory and by the difference in the diffuseness of the atomic basis functions between the first- and second-row atoms

Disilane radical anion has been investigated as a prototype of polysilane anions by ab initio molecular orbital theory. Disilane in a D 3d structure is distorted to a C 2h structure by receiving an electron. In the C 2h minimum geometry, disilane anion has a 2 B u electronic structure with an unpaired electron occupying a Si-Si antibonding σ * orbital (b u ) with a large Si s diffuse orbital contribution. It is found to be a kinetically bound anion. No Si 3d orbital participation is found in this anion. These results suggest that more stable polysilane anions also have the same kind of molecular and electronic structures.

Quantum chemical calculation is applied to investigate the reaction mechanism of sulfonyl acid generator and the transparency of the resist material. We have found that electron absorbed dimethylsulfone can be easily decomposed by relatively low energy (2.95 Kcal/mol), reaching to the decomposed status of methyl radical and methyl sulfonyl anion. This was thought to be an initial step in the electron acid generation reaction of the sulfonyl compounds. The total molecular energy of dimethyl sulfone anion was found to be higher than that of the neutral dimethylsulfone. On the other hand, sulfone derivatives with electron-withdrawing groups, such as methyl sulfonyl acetonitrile, usually have higher energy (about 41 kcal/mol) than those for their anion. This suggests that the electron withdrawing groups enhance the electron affinity of the sulfone compounds, which are also considered to increase the efficiency of acid generation. Additionally, another quantum chemical study was carried out in order to improve transparency of the aromatic species in resist for ArF excimer laser. Using configuration interaction (CI) methods of molecular orbital theory, the substituent effects of UV absorption in the aromatic compounds were investigated. As a result, significant red sifts in Amax were observed in the conjugated aromatic rings, which increases the transparency at 193 nm wavelength region.

The correlation between the electronic structure and C—H bond scission efficiency upon exposure to ionizing radiation in relatively simple hydrocarbons has been studied by the extended Huckel and ab initio molecular orbital methods. GF(HOMO) values, which are derived from the overlap populations of the C—H bond in the HOMO [FHOMO(C—H) values], are found to be closely correlated with the experimental G(H2) values. This provides an expedient procedure for estimating C—H bond scission efficiency induced by ionizing radiation, without resorting to time-consuming and expensive theoretical models. Considering the reported experimental results in conjunction with the calculated results, this correlation can be explained mainly in terms of HOMO—SOMO bimolecular frontier-orbital interactions. The calculated results also indicate that C—H bond scission efficiency strongly depends upon the conformation of the C—C framework.