Effect of molecular and electronic structure on the light harvesting properties of dye sensitizers

The systematic trends in structural and electronic properties of perylene diimide (PDI) derived dye molecules have been investigated by DFT calculations based on projector augmented wave (PAW) method including gradient corrected exchange-correlation effects. TDDFT calculations have been performed to study the visible absorbance activity of these complexes. The effect of different ligands and halogen atoms attached to PDI were studied to characterize the light harvesting properties. The atomic size and electronegativity of the halogen were observed to alter the relaxed molecular geometries which in turn influenced the electronic behavior of the dye molecules. Ground state molecular structure of isolated dye molecules studied in this work depends on both the halogen atom and the carboxylic acid groups. DFT calculations revealed that the carboxylic acid ligands did not play an important role in changing the HOMO-LUMO gap of the sensitizer. However, they serve as anchor between the PDI and substrate titania surface of the solar cell or photocatalyst. A commercially available dye-sensitizer, ruthenium bipyridine (RuBpy), was also studied for electronic and structural properties in order to make a comparison with PDI derivatives for light harvesting properties. Results of this work suggest that fluorinated, chlorinated, brominated, and iyodinated PDI compounds can be useful as sensitizers in solar cells and in artificial photosynthesis.Comment: Single pdf file, 14 pages with 7 figures and 4 table

Loss of KCNJ10 protein expression abolishes endocochlear potential and causes deafness in Pendred syndrome mouse model

BACKGROUND: Pendred syndrome, a common autosomal-recessive disorder characterized by congenital deafness and goiter, is caused by mutations of SLC26A4, which codes for pendrin. We investigated the relationship between pendrin and deafness using mice that have (Slc26a4(+/+)) or lack a complete Slc26a4 gene (Slc26a4(-/-)). METHODS: Expression of pendrin and other proteins was determined by confocal immunocytochemistry. Expression of mRNA was determined by quantitative RT-PCR. The endocochlear potential and the endolymphatic K(+ )concentration were measured with double-barreled microelectrodes. Currents generated by the stria marginal cells were recorded with a vibrating probe. Tissue masses were evaluated by morphometric distance measurements and pigmentation was quantified by densitometry. RESULTS: Pendrin was found in the cochlea in apical membranes of spiral prominence cells and spindle-shaped cells of stria vascularis, in outer sulcus and root cells. Endolymph volume in Slc26a4(-/- )mice was increased and tissue masses in areas normally occupied by type I and II fibrocytes were reduced. Slc26a4(-/- )mice lacked the endocochlear potential, which is generated across the basal cell barrier by the K(+ )channel KCNJ10 localized in intermediate cells. Stria vascularis was hyperpigmented, suggesting unalleviated free radical damage. The basal cell barrier appeared intact; intermediate cells and KCNJ10 mRNA were present but KCNJ10 protein was absent. Endolymphatic K(+ )concentrations were normal and membrane proteins necessary for K(+ )secretion were present, including the K(+ )channel KCNQ1 and KCNE1, Na(+)/2Cl(-)/K(+ )cotransporter SLC12A2 and the gap junction GJB2. CONCLUSIONS: These observations demonstrate that pendrin dysfunction leads to a loss of KCNJ10 protein expression and a loss of the endocochlear potential, which may be the direct cause of deafness in Pendred syndrome

Crystal engineering as a tool for directed radiationless energy transfer in layered {Λ-[Ru(bpy)₃] Δ-[Os(bpy)₃]} (PF₆)₄

New types of crystal structures with new physical properties such as energy harvesting can be engineered by exploiting the potentiality of chiral recognition. In the proposed strategy one takes advantage of the possibility that in true racemates one enantiomeric component in the crystal packing may be replaced by a different molecule of the same chirality and similar shape. This opens the path to a number of new properties. In the present investigation, we demonstrate that a system can be engineered, in which homochiral layers of Λ-[Ru(bpy)₃]²⁺ rigorously alternate with homochiral layers of Δ-[Os(bpy)₃]²⁺. This arrangement is realized in Λ-[Ru(bpy)₃]Δ-[Os(bpy)₃]}(PF₆)₄. Due to the deliberately introduced lower dimensionality, the new crystalline system exhibits fascinating properties, in particular with respect to an interplay of processes of interlayer and intralayer radiationless energy transfer. Interestingly, in this system it is possible to achieve a controlled accumulation of excitation energy on a single crystallographic Δ-[Os(bpy)₃]²⁺ site. Moreover, the excitation energy is absorbed in a wide range from the UV to the red side of the visible by both Λ-[Ru(bpy)₃]²⁺ and Δ-[Os(bpy)₃]²⁺ units, and one observes an intense red/infrared and highly resolved emission only of the low-energy Δ-[Os(bpy)₃]²⁺ site, irrespective of the excitation wavelength used. The crystal structure of this newly engineered compound is determined for both the room-temperature phase (P32, a = 10.7012(5) Å, c = 16.3490(10) Å) as well as for the low-temperature phase (P3, a = 18.4189(10) Å, c ) 16.2309(9) Å)