Nonequilibrium processes occurring in functional materials can significantly impact device efficiencies and are often difficult to characterize due to the broad range of length and time scales involved. In particular, mixed halide hybrid perovskites are promising for optoelectronics, yet the halides reversibly phase separate when photo-excited, significantly altering device performance. By combining nanoscale imaging and multiscale modeling, we elucidate the mechanism underlying this phenomenon, demonstrating that local strain induced by photo-generated polarons promotes halide phase separation and leads to nucleation of light-stabilized iodide-rich clusters. This effect relies on the unique electromechanical properties of hybrid materials, characteristic of neither their organic nor inorganic constituents alone. Exploiting photo-induced phase separation and other nonequilibrium phenomena in hybrid materials, generally, could enable new opportunities for expanding the functional applications in sensing, photoswitching, optical memory, and energy storage.Photovoltaic and light-emitting devices typically operate under conditions far from equilibrium. As such, elucidating the response of functional materials to nonequilibrium driving forces is vital to understanding their fundamental properties and to determining their suitability for device applications. In particular, photo-induced dynamic processes are of major importance to the performance of hybrid perovskite-based devices.1-3 Hybrid perovskites are low-cost, solution processable materials that are promising for many device applications, including photovoltaics 4-9 and light-emitting diodes (LEDs). 10The high device efficiencies have been attributed to their high brightness, long charge carrier migration lengths, + 2 , FA), and X is either iodide, bromide, chloride, or iodide/bromide or bromide/chloride mixtures. By varying the halide ratios in hybrid perovskites, the bandgap can be tuned across the visible spectrum.1,14,15 Precise control of the bandgap presents promising opportunities for color tuning perovskite-based LEDs and lasers, and for incorporating hybrid perovskites in tandem solar cells. 9,16Light-induced effects, however, restrict the practical use of mixed halide hybrid perovskites.1,17,18 Photoluminescence (PL) and X-ray diffraction (XRD) measurements suggest that MAPb(I x Br 1−x ) 3 (0.1 < x < 0.8) undergoes reversible phase separation into iodide-rich and bromiderich regions when photo-excited.1 Such demixing is detrimental to photovoltaic performance, since it leads to charge carrier trapping in the iodide-rich regions. Determining the microscopic mechanism behind phase separation is essential for furthering approaches to mitigate adverse photo-induced effects in devices and should expand the range of their functional applications into areas such as optical memory storage and sensing.19,20 Unfortunately, the microscopic mechanism behind this effect has been elusive because of the multiple length and time scales involved in characterizing the ...

SUMMARY Multimeric, ring-shaped molecular motors rely on the coordinated action of their subunits to perform crucial biological functions. During these tasks, motors often change their operation in response to regulatory signals. Here, we investigate a viral packaging machine as it fills the capsid with DNA and encounters increasing internal pressure. We find that the motor rotates the DNA during packaging and that the rotation per basepair increases with filling. This change accompanies a reduction in the motor’s step size. We propose that these adjustments preserve motor coordination by allowing one subunit to make periodic, specific, and regulatory contacts with the DNA. At high filling, we also observe the down-regulation of the ATP-binding rate and the emergence of long-lived pauses, suggesting a throttling-down mechanism employed by the motor near the completion of packaging. This study illustrates how a biological motor adjusts its operation in response to changing conditions, while remaining highly coordinated.

SUMMARY Ring NTPases of the ASCE superfamily perform a variety of cellular functions. An important question about the operation of these molecular machines is how the ring subunits coordinate their chemical and mechanical transitions. Here, we present a comprehensive mechanochemical characterization of a homomeric ring ATPase—the bacteriophage φ29 packaging motor—a homopentamer that translocates double-stranded DNA in cycles composed of alternating dwells and bursts. We use high-resolution optical tweezers to determine the effect of nucleotide analogs on the cycle. We find that ATP hydrolysis occurs sequentially during the burst and that ADP release is interlaced with ATP binding during the dwell, revealing a high degree of coordination among ring subunits. Moreover, we show that the motor displays an unexpected division of labor: although all subunits of the homopentamer bind and hydrolyze ATP during each cycle, only four participate in translocation, whereas the remaining subunit plays an ATP-dependent regulatory role.

The bacteriophage ϕ29 generates large forces to compact its double-stranded DNA genome into a protein capsid by means of a portal motor complex. Several mechanical models for the generation of these high forces by the motor complex predict coupling of DNA translocation to rotation of the head-tail connector dodecamer. Putative connector rotation is investigated here by combining the methods of single-molecule force spectroscopy with polarization-sensitive single-molecule fluorescence. In our experiment, we observe motor function in several packaging complexes in parallel using video microscopy of bead position in a magnetic trap. At the same time, we follow the orientation of single fluorophores attached to the portal motor connector. From our data, we can exclude connector rotation with greater than 99% probability and therefore answer a long-standing mechanistic question.