Dye‐sensitized solar cells (DSSCs) based on organic dyes adsorbed on nanocrystalline TiO2 electrodes have received considerable attention because of their high incident solar light‐to‐electricity conversion efficiency and low cost of production. A number of organic dyes have so far been developed, and the relationship between their chemical structures and the photovoltaic performances of DSSCs based on the dyes has been examined. To create high‐performance DSSCs, it is important to develop effective organic dye sensitizers, which should be optimized for the chemical structures to possess good light‐harvesting features, to provide good electron communication between the dyes and a TiO2 electrode, and to control the molecular arrangements on the TiO2 electrode. The aim of this microreview is to highlight the design and synthesis of organic dyes for DSSCs based on recent work of organic chemists. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The authors have noticed an error in the structure of compound PS-1 in Scheme 1 of their Review. The corrected version of PS-1 is presented below. The authors apologize for this error and for any inconvenience caused.

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.

Dithienogermole-containing π-conjugated polymers were prepared by the Stille coupling reactions of distannyldithienogermole and dibromoarenes. The polymers exhibit optical properties similar to those of the previously reported silicon analogues and are usable as the active materials for bulk heterojunction-type organic photovoltaic cells as blends with PC70BM.

A new-type of donor-acceptor π-conjugated (D-π-A) fluorescent dyes NI3-NI8 with a pyridine ring as electron-withdrawing-injecting anchoring group have been developed and their photovoltaic performances in dye-sensitized solar cells (DSSCs) are investigated. The short-circuit photocurrent densities and solar energy-to-electricity conversion yields of DSSCs based on NI3-NI8 are greater than those for the conventional D-π-A dye sensitizers NI1 and NI2 with a carboxyl group as the electron-withdrawing anchoring group. The IR spectra of NI3-NI8 adsorbed on TiO(2) indicate the formation of coordinate bonds between the pyridine ring of dyes NI3-NI8 and the Lewis acid sites (exposed Ti(n+) cations) of the TiO(2) surface. This work demonstrates that the pyridine rings of D-π-A dye sensitizers that form a coordinate bond with the Lewis acid site of a TiO(2) surface are promising candidates as not only electron-withdrawing anchoring group but also electron-injecting group, rather than the carboxyl groups of the conventional D-π-A dye sensitizers that form an ester linkage with the Brønsted acid sites of the TiO(2) surface.

Mechanochromic organic molecules (MOMs) that exhibit a large difference of fluorescence wavelength between two states have important potential applications, but few such compounds are known. Here, we report a new MOM, cis-ABPX01(0), which shows switchable near-IR and blue fluorescence responses. Detailed spectrophotometric and single-crystal X-ray analyses revealed that the near-IR fluorescence is attributable to fluorescence from slip-stacked dimeric structures in crystals, while the blue fluorescence is attributable to fluorescence from the monomer. Switching between the two is achieved by dynamic structural interconversion between the two molecular packing arrangements in response to mechanical grinding and solvent vapor-fuming.

Anthracene-boronic acid ester as a new class of fluorescence PET sensors for detection of a trace amount of water in organic solvents has been designed and developed.