A series of four ullazine-donor based donor-π bridge-acceptor (D-π-A) dyes have been synthesized and compared to a prior ullazine donor-acceptor (D-A) dye as well as a triphenylamine donor with an identical π-bridge and acceptor. The D-π-A ullazine series demonstrates an unusually uniform-in-intensity panchromatic UV/Vis absorption spectrum throughout the visible region. This is in part due to the introduction of strong high-energy bands through incorporation of the ullazine building block as shown by computational analysis. The dyes were characterized on TiO films and in DSC devices. Performances of 5.6 % power conversion efficiency were obtained with IPCE onsets reaching 800 nm.

Hydrogenase enzymes produce H 2 gas, which can be a potential source of alternative energy. Inspired by the [NiFe] hydrogenases, we report the construction of a de novo-designed artificial hydrogenase (ArH). The ArH is a dimeric coiled coil where two cysteine (Cys) residues are introduced at tandem a/d positions of a heptad to create a tetrathiolato Ni binding site. Spectroscopic studies show that Ni binding significantly stabilizes the peptide producing electronic transitions characteristic of Ni-thiolate proteins. The ArH produces H 2 photocatalytically, demonstrating a bell-shaped pH-dependence on activity. Fluorescence lifetimes and transient absorption spectroscopic studies are undertaken to elucidate the nature of pHdependence, and to monitor the reaction kinetics of the photochemical processes. pH titrations are employed to determine the role of protonated Cys on reactivity. Through combining these results, a fine balance is found between solution acidity and the electron transfer steps. This balance is critical to maximize the production of Ni I -peptide and protonation of the Ni II À H À intermediate (NiÀ R) by a Cys (pK a � 6.4) to produce H 2 .

Metal-free bis-cyclopentadithiophene-based molecular sensitizers with varying halogens (Cl, Br, and I) installed at a terminal position in conjugation with the dye frontier molecular orbital π-system are studied in combination with two cobalt redox shuttles (RSs): with and without a nonmetal-coordinated nitrogen atom (pyrazine or pyridine) accessible to the halide-decorated dyes. This systematic study employs UV−vis absorption, cyclic voltammetry, density functional theory calculations, and nanosecond transient absorption spectroscopy to probe the influence of possible halogen-bonding between the dyes and the pyrazine-based RS on electron-transfer reactions and effects on dye-sensitized solar cell performances. The results of this study imply a possible halogen-bonding event occurring between the halogenated dyes and the halogen binding RS with substantial effects on electrontransfer reaction rates.

Irradiation at 460 nm of [Mo 3 (μ 3 -S)(μ 2 -S 2 ) 3 (S 2 CNR 2 ) 3 ]I ([2a]I, R = Me; [2b]I, R = Et; [2c]I, R = i Bu; [2d]I, R = CH 2 C 6 H 5 ) in a mixed aqueous−polar organic medium with [Ru(bipy) 3 ] 2+ as photosensitizer and Et 3 N as electron donor leads to H 2 evolution. Maximum activity (300 turnovers, 3 h) is found with R = i Bu in 1:9 H 2 O:MeCN; diminished activity is attributed to deterioration of [Ru(bipy) 3 ] 2+ . Monitoring of the photolysis mixture by mass spectrometry suggests transformation of [Mo 3 (μ 3 -S)(μ 2 -S 2 ) 3 (S 2 CNR 2 ) 3 ] + to [Mo 3 (μ 3 -S)(μ 2 -S) 3 (S 2 CNR 2 ) 3 ] + via extrusion of sulfur on a time scale of minutes without accumulation of the intermediate [Mo 3 S 6 (S 2 CNR 2 ) 3 ] + or [Mo 3 S 5 (S 2 CNR 2 ) 3 ] + species. Deliberate preparation of [Mo 3 S 4 (S 2 CNEt 2 ) 3 ] + ([3] + ) and treatment with Et 2 NCS 2 1− yields [Mo 3 S 4 (S 2 CNEt 2 ) 4 ] ( 4), where the fourth dithiocarbamate ligand bridges one edge of the Mo 3 triangle. Photolysis of 4 leads to H 2 evolution but at ∼25% the level observed for [Mo 3 S 7 (S 2 CNEt 2 ) 3 ] + . Early time monitoring of the photolyses shows that [Mo 3 S 4 (S 2 CNEt 2 ) 4 ] evolves H 2 immediately and at constant rate, while [Mo 3 S 7 (S 2 CNEt 2 ) 3 ] + shows a distinctive incubation prior to a more rapid H 2 evolution rate. This observation implies the operation of catalysts of different identity in the two cases.

The thienopyrazine (TPz) building block allows for NIR photon absorption in dye-sensitized solar cells (DSCs) when used as a π-bridge. We synthesized and characterized 7 organic sensitizers employing thienopyrazine (TPz) as a π-bridge in a double donor, double acceptor organic dye design. Donor groups are varied based on electron donating strength and sterics at the donor-π bridge bond with the acceptor groups varied as either carboxylic acids or benzoic acids on the π-bridge. This dye design was found to be remarkably tunable with solution absorption onsets ranging from 750 to near 1000 nm. Interestingly, the solution absorption measurements do not accurately approximate the dye absorption on TiO films with up to a 250 nm blue-shift of the dye absorption onset on TiO. This shift in absorption and the effect on electron transfer properties is investigated via computational analysis, time-correlated single photon counting studies, and transient absorption spectroscopy. Structure-performance relationships were analyzed for the dyes in DSC devices with the highest performance observed at 17.6 mA/cm of photocurrent and 7.5% PCE for a cosensitized device with a panchromatic IPCE onset of 800 nm.