Firmly attached: The short‐circuit photocurrent density and conversion yields of solar cells based on pyridine‐containing donor–acceptor π‐conjugated (D‐π‐A) dyes (see scheme) are greater than those for conventional D‐π‐A dye sensitizers that bear a carboxy group as the electron‐withdrawing anchoring group. The dyes are attached to the surface by coordinate bonding with the Lewis acid sites of TiO2.

Molecular oxygen species formed on the surface of partially reduced TiO 2 (rutile) nanoparticles have been studied by in situ electron spin resonance (ESR) and diffuse-reflectance spectroscopies. ESR signals due to O 2 -(g z ) 2.020) and Ti 3+ appeared upon visible-light illumination at 77 K and vanished by raising the temperature in the dark. The numbers of O 2 and Ti 3+ radicals formed by sub-band-gap illumination were equal, suggesting a reversible electron transfer between peroxo O 2 2species and the adjacent Ti 4+ ion at an oxygen vacancy site on the TiO 2 surface:The ESR intensity was saturated by a prolonged illumination and a surface coverage of O 2 molecules adsorbed at the oxygen vacancy site was evaluated as 1.3 × 10 13 sites cm -2 . The spectral response for the generation rate of O 2 exhibited a broad peak at around 480 nm, in agreement with the absorption band observed by the diffuse-reflectance measurements. It was concluded that F-type color centers generated in subsurface layers of TiO 2 absorb the visible light to induce indirectly the electron-transfer reaction from O 2 2to Ti 4+ at the surface oxygen vacancy site.

High-resolution EPR spectra of CH 3 , 13 CH 3 , and even CH 2 D radicals with their natural abundances have been observed in Ar matrix in the temperature range 4.2-40 K. This was achieved by X-ray radiolysis of Ar matrix containing 0.2 mol % CH 4 . The high-resolution EPR spectra of CD 3 and CHD 2 radicals were also obtained under similar conditions using CD 4 and CH 2 D 2 instead of CH 4 , respectively. At the lower temperatures, the EPR line shapes of these radicals are dominated by hyperfine (hf) patterns with anomalous intensity, attributed to quantum effects. The application of the Pauli principle in combination with D 3 point-group symmetry results in interesting exclusion of EPR transitions for both the R-proton-and the R-deuteron-rotor spectra. In contrast to the -proton methyls > • C-CH 3 , the hf coupling is anisotropic and no rotation-hindering barrier is present here. The "E" lines of the corresponding isotropic -proton methyl rotor Benetis, N. P. Chem. Phys. 1998, 226, 151] 1 are absent from their regular positions. The deuteron rotor is giving a peculiar spectrum at the lowest experimental temperature, i.e., an extremely strong central singlet superimposed on a much weaker fast motional spectrum. The quantum effects are attributed to spin-rotation coupling through the anisotropic part of the hf interaction and exchange symmetry of at least two identical fermions or bosons of the studied radicals. The experimental findings are consistent with a three-dimensional, free quantum-rotor motional model.