Traditional CdSe-based colloidal quantum dots (cQDs) have interesting photoluminescence (PL) properties. Herein we highlight the advantages in both ensemble and single-nanocrystal PL of colloidal CsPbBr 3 nanocrystals (NCs) over the traditional cQDs.A ne nsemble of colloidal CsPbBr 3 NCs (11 nm) exhibits ca. 90 %P Lq uantum yield with narrow( FWHM = 86 meV) spectral width. Interestingly, the spectral width of as ingle-NC and an ensemble are almost identical, ruling out the problem of size-distribution in PL broadening. Eliminating this problem leads to an egligible influence of self-absorption and Fçrster resonance energy transfer,a long with batch-to-batch reproducibility of NCs exhibiting PL peaks within AE 1nm. Also,PLpeak positions do not alter with measurement temperature in the range of 25 to 100 8 8C. Importantly,C sPbBr 3 NCs exhibit suppressed PL blinking with ca. 90 %o ft he individual NCs remain mostly emissive (on-time > 85 %), without muchi nfluence of excitation power.The CsPbX 3 (X = Cl, Br,o rI )p erovskite was reported by Møller in 1958.[1] Mitzi and co-workers showed the interesting optoelectronic properties of organic-inorganic perovskite materials about twenty years ago. [2] In about the last six years,s olution-processed organic-inorganic hybrid perovskites,s uch as CH 3 NH 3 PbI 3 ,b ecame one of the most celebrated materials because they exhibit nearly 20 %s olarcell efficiency.[3] This success of bulk perovskite,a lso prompted af ew reports on colloidal nanocrystals (NCs) of MPbX 3 (M = CH 3 NH 3 and Cs;X = Cl, Br, and I), where intense photoluminescence (PL) has been the main property.[4] Herein, we establish that PL from CsPbBr 3 perovskite NCs is intrinsically different and advantageous,c ompared to that from traditional colloidal quantum dots (cQDs).State of the art, highly luminescent CdSe-based cQDs, particularly,c ore-shell NCs found applications in highdefinition displays because of the narrower full width at half maxima (FWHM) of their PL compared to that of organic dyes.[5] Kovalenko et al. [4b] reported early this year that CsPbX 3 (X = Cl, Br, and I) NCs exhibit around 90 %P L efficiency with narrow FWHM, which is superior to most CdSe-based NCs obtained even after surface modifications. Tr aditional CdSe based cQDs exhibit intense PL only when the size of NC (ca. 5nm) is comparable to the Bohr excitonic diameter, where strong quantum confinement of charge carriers enhances the transition probability.T his requirement of quantum confinement, however,r esults into spectral broadening from the size-distribution, and ah igh density of trap states because of the large surface to volume ratio. [6] Owing to the size-distribution problem where smaller sized NCs exhibit higher optical gap compared to larger sized ones,c hromaticity and quantum yield (QY) of PL changes with concentration of NCs because of both self-absorption and Fçrster resonance energy transfer (FRET).[7] Also,since the optical gap of such luminescent cQD is strongly dependent on the size of the NCs,reprodu...

doi: bioRxiv preprint their components rapidly with the surrounding medium (Hyman et al., 2014;. Most of the liquid condensates possess common characteristics, which include their formation mechanism as well as their physical properties. For instance, multivalent proteins or nucleic acids associate through weak intermolecular interactions and reach a solubility limit to form liquid condensates (Banani et al., 2017;. These condensates are highly mobile, spherical, but get deformed on physical contact, fuse and eventually relax back to their spherical shape (Brangwynne et al., 2009;Brangwynne et al., 2011;Molliex et al., 2015;Nott et al., 2015). Several proteins undergoing LLPS, however, contain intrinsically disordered regions (IDRs) that are closely associated with prion-like domains (PLDs) and low complexity domains (LCDs) (

The ability of proteins to locate specific sites or structures among a vast excess of nonspecific DNA is a fundamental theme in biology. Yet the basic principles that govern these mechanisms remain poorly understood. For example, mismatch repair proteins must scan millions of base pairs to find rare biosynthetic errors, and they then must probe the surrounding region to identify the strand discrimination signals necessary to distinguish the parental and daughter strands. To determine how these proteins might function we used single-molecule optical microscopy to answer the following question: how does the mismatch repair complex Msh2-Msh6 interrogate undamaged DNA? Here we show that Msh2-Msh6 slides along DNA via one-dimensional diffusion. These findings indicate that interactions between Msh2-Msh6 and DNA are dominated by lateral movement of the protein along the helical axis and have implications for how MutS family members travel along DNA at different stages of the repair reaction.

Traditional CdSe‐based colloidal quantum dots (cQDs) have interesting photoluminescence (PL) properties. Herein we highlight the advantages in both ensemble and single‐nanocrystal PL of colloidal CsPbBr3 nanocrystals (NCs) over the traditional cQDs. An ensemble of colloidal CsPbBr3 NCs (11 nm) exhibits ca. 90 % PL quantum yield with narrow (FWHM=86 meV) spectral width. Interestingly, the spectral width of a single‐NC and an ensemble are almost identical, ruling out the problem of size‐distribution in PL broadening. Eliminating this problem leads to a negligible influence of self‐absorption and Förster resonance energy transfer, along with batch‐to‐batch reproducibility of NCs exhibiting PL peaks within ±1 nm. Also, PL peak positions do not alter with measurement temperature in the range of 25 to 100 °C. Importantly, CsPbBr3 NCs exhibit suppressed PL blinking with ca. 90 % of the individual NCs remain mostly emissive (on‐time >85 %), without much influence of excitation power.

No abstract

Supramolecular block copolymerzation with optically or electronically complementary monomers provides an attractive bottomup approach for the non-covalent synthesis of nascent axial organic heterostructures, which promises to deliver useful applications in energy conversion, optoelectronics, and catalysis. However, the synthesis of supramolecular block copolymers (BCPs) constitutes a significant challenge due to the exchange dynamics of non-covalently bound monomers and hence requires fine microstructure control. Furthermore, temporal stability of the segmented microstructure is a prerequisite to explore the applications of functional supramolecular BCPs. Herein, we report the cooperative supramolecular block copolymerization of fluorescent monomers in solution under thermodynamic control for the synthesis of axial organic heterostructures with light-harvesting properties. The fluorescent nature of the core-substituted naphthalene diimide (cNDI) monomers enables a detailed spectroscopic probing during the supramolecular block copolymerization process to unravel a nucleation−growth mechanism, similar to that of chain copolymerization for covalent block copolymers. Structured illumination microscopy (SIM) imaging of BCP chains characterizes the segmented microstructure and also allows size distribution analysis to reveal the narrow polydispersity (polydispersity index (PDI) ≈ 1.1) for the individual block segments. Spectrally resolved fluorescence microscopy on single block copolymerized organic heterostructures shows energy migration and light-harvesting across the interfaces of linearly connected segments. Molecular dynamics and metadynamics simulations provide useful mechanistic insights into the free energy of interaction between the monomers as well as into monomer exchange mechanisms and dynamics, which have a crucial impact on determining the copolymer microstructure. Our comprehensive spectroscopic, microscopic, and computational analyses provide an unambiguous structural, dynamic, and functional characterization of the supramolecular BCPs. The strategy presented here is expected to pave the way for the synthesis of multi-component organic heterostructures for various functions.

Studies on diffusion dynamics of single molecules (SMs) have been useful in revealing inhomogeneity of polymer thin films near and above the glass-transition temperature (T(g)). However, despite several applications of polymer thin films where exposure to solvent (or vapor) is common, the effect of absorbed solvent molecules on local morphology and rigidity of polymer matrices is yet to be explored in detail. High-T(g) hydrophilic polymers such as poly(vinylpyrrolidone) (PVP) are used as pharmaceutical coatings for drug release in aqueous medium, as they readily absorb moisture, which results in effective lowering of the T(g) and thereby leads to plasticization. The effect of moisture absorption on swelling and softening of PVP thin films was investigated by visualizing the diffusion dynamics of rhodamine 6G (Rh6G) tracer molecules at various ambient relative humidities (RH). Wide-field epifluorescence microscopy, in conjunction with high-resolution SM tracking, was used to monitor the spatiotemporal evolution of individual tracers under varied moisture contents of the matrix. In the absence of atmospheric moisture, Rh6G molecules in dry PVP films are translationally inactive, suggestive of rigid local environments. Under low moisture contents (RH 30-50%), translational mobility remains arrested but rotational motion is augmented, indicating slight swelling of the polymer network which marks the onset of plasticization. The translational mobility of Rh6G was found to be triggered only at a threshold ambient RH, beyond which a large proportion of tracers exhibit extensive diffusion dynamics. Interestingly, SM tracking data at higher moisture contents of the film (RH ≥ 60%) reveal that the distributions of dynamic parameters (such as diffusivity) are remarkably broad, spanning several orders of magnitude. Furthermore, Rh6G molecules display a wide variety of translational motion even at a fixed ambient RH, clearly pointing out the extremely inhomogeneous environment of plasticized PVP network. Intriguingly, it is observed that a majority of tracers undergo anomalous subdiffusion even under high moisture contents of the matrix. Analyses of SM trajectories using velocity autocorrelation function reveal that subdiffusive behaviors of Rh6G are likely to originate from fractional Brownian motion, a signature of tracer dynamics in viscoelastic medium.

A propeller-shaped perylene diimide trimer was synthesized and a simple evaporation method was used for the self-organization of trimer molecules into fluorescent nanofibers. The sizes of these fibers-from 4 to 150 nm in diameter-were measured by atomic force microscopy and can be controlled by adjusting the concentration of the initial solution. The aspect ratios (length/height) are around 500. The plane of the trimer was determined by polarized scanning confocal microscopy to be perpendicular to the axis of the fibers, in agreement with molecular mechanics calculations. UV/vis and NMR spectroscopies were used to monitor concentration-dependent pi-pi stacking in solution. Single-fiber fluorescence imaging and spectroscopy were performed using a total internal reflection fluorescence microscope equipped with a digital color camera and imaging CCD spectrometer. Strongly red-shifted fluorescence from these fibers indicates a high degree of electronic delocalization, and breaking up this delocalization by photobleaching blue-shifts the emission toward that of an isolated noninteracting molecule. The delocalization along these nanofibers and the ability to study the electronic structure using fluorescence make them potentially useful in nanoscale devices, such as field effect transistors and photoconductors.