The large multiprotein complex, photosystem I (PSI), which is at the heart of light-dependent reactions in photosynthesis, is integrated as the active component in a solid-state organic photovoltaic cell. These experiments demonstrate that photoactive megadalton protein complexes are compatible with solution processing of organic-semiconductor materials and operate in a dry non-natural environment that is very different from the biological membrane.

Biological functions frequently require protein–protein interactions that involve secondary and tertiary structural perturbation. Here we study protein–protein dissociation and reassociation dynamics in insulin, a model system for protein oligomerization. Insulin dimer dissociation into monomers was induced by a nanosecond temperature-jump (T-jump) of ~8 °C in aqueous solution, and the resulting protein and solvent dynamics were tracked by time-resolved X-ray solution scattering (TRXSS) on time scales of 10 ns to 100 ms. The protein scattering signals revealed the formation of five distinguishable transient species during the association process that deviate from simple two-state kinetics. Our results show that the combination of T-jump pump coupled to TRXSS probe allows for direct tracking of structural dynamics in nonphotoactive proteins.

Photoexcited molecular trajectories on potential energy surfaces (PESs) prior to thermalization are intimately connected to the photochemical reaction outcome. The excited-state trajectories of a diplatinum complex featuring photo-activated metal-metal σ-bond formation and associated PtÀ Pt stretching motions were detected in real time using femtosecond wide-angle Xray solution scattering. The observed motions correspond well with coherent vibrational wavepacket motions detected by femtosecond optical transient absorption. Two key coordinates for intersystem crossing have been identified, the PtÀ Pt bond length and the orientation of the ligands coordinated with the platinum centers, along which the excited-state trajectories can be projected onto the calculated PESs of the excited states. This investigation has gleaned novel insight into electronic transitions occurring on the time scales of vibrational motions measured in real time, revealing ultrafast nonadiabatic or non-equilibrium processes along excited-state trajectories involving multiple excited-state PESs.

The structural dynamics of insulin hexamer dissociation were studied by the photoinduced temperature jump technique and monitored by time-resolved X-ray scattering. The process of hexamer dissociation was found to involve several transient intermediates, including an expanded hexamer and an unstable tetramer. Our findings provide insights into the mechanisms of protien-protein association.

Photosynthesis is Nature's major process for converting solar into chemical energy. One of the key players in this process is the multiprotein complex photosystem I (PSI) that through absorption of incident photons enables electron transfer, which makes this protein attractive for applications in bioinspired photoactive hybrid materials. However, the efficiency of PSI is still limited by its poor absorption in the green part of the solar spectrum. Inspired by the existence of natural phycobilisome light-harvesting antennae, we have widened the absorption spectrum of PSI by covalent attachment of synthetic dyes to the protein backbone. Steady-state and time-resolved photoluminescence reveal that energy transfer occurs from these dyes to PSI. It is shown by oxygen-consumption measurements that subsequent charge generation is substantially enhanced under broad and narrow band excitation. Ultimately, surface photovoltage (SPV) experiments prove the enhanced activity of dye-modified PSI even in the solid state.

The next generation of optoelectronic devices requires transparent conductive electrodes to be flexible, cheap, and compatible with large scale manufacturing processes. Indium Tin Oxide (ITO) electrodes are often used due to their superior transparency and conductance, however they are brittle, expensive and their fabrication requires vacuum conditions which restrict scale-up. One possible alternative to the traditional ITO electrode is the metal nanowire mesh (MNWM) electrode, which is transparent, conductive, flexible and easy to produce. In this work we present the preparation and characterization of a simple organic light emitting diode (OLED) device based on a transparent electrode made of ultrathin MNWM and a comparison to an ITO based device. We have found that MNWM electrodes offer a suitable alternative to ITO electrodes in OLED devices. We have also found that the failure rate for devices due to short circuits between the top and bottom electrodes was smaller in MNWM based devices compared to ITO based devices since the MNWM devices could be repaired to present normal OLED behavior by selectively burning the nanowires forming the short. The ability to ''heal'' organic devices presents an important advantage and also allows for future uses in applications such as roll to roll printing.

Direct tracking of protein structural dynamics during folding-unfolding processes is important for understanding the roles of hierarchic structural factors in the formation of functional proteins. Using cytochrome c (cyt c) as a platform, we investigated its structural dynamics during folding processes triggered by local environmental changes (i.e., pH or heme iron center oxidation/spin/ligation states) with time-resolved X-ray solution scattering measurements. Starting from partially unfolded cyt c, a sudden pH drop initiated by light excitation of a photoacid caused a structural contraction in microseconds, followed by active site restructuring and unfolding in milliseconds. In contrast, the reduction of iron in the heme via photoinduced electron transfer did not affect conformational stability at short timescales (<1 ms), despite active site coordination geometry changes. These results demonstrate how different environmental perturbations can change the nature of interaction between the active site and protein conformation, even within the same metalloprotein, which will subsequently affect the folding structural dynamics.

The nature of the photoexcited state of octabutoxy nickel(II) phthalocyanine (NiPcOBu ) with a 500 ps lifetime was investigated by X-ray transient absorption (XTA) spectroscopy. Previous optical, vibrational, and computational studies have suggested that this photoexcited state has a ligand-to-metal charge transfer (LMCT) nature. By using XTA, which provides unambiguous information on the local electronic and nuclear configuration around the Ni center, the nature of the excited state of NiPcOBu was reassessed. Using X-ray probe pulses from a synchrotron source, the ground- and excited-state X-ray absorption spectra of NiPcOBu were measured. Based on the results, we identified that the excited state exhibits spectral features that are characteristic of a Ni (3dz2 ,3dx2-y2 ) state rather than a LMCT state with a transiently reduced Ni center. This state resembles the (d,d) state of nickel(II) tetramesitylphorphyrin. The XTA features are rationalized based on the inherent cavity sizes of the macrocycles. These results may provide useful guidance for the design of photocatalysts in the future.