Despite tremendous progress in optoelectronic devices using lead perovskite (CH3NH3(+)PbI3(-)), there has been a paucity of mechanistic information on how photoactive micron-sized crystals of lead perovskite grow from a mixture of a layered crystal of lead(II) iodide and methylammonium iodide mediated by a polar solvent, DMSO or DMF. We report here that the whole process of the lead perovskite synthesis consists of a series of equilibria driven by reversible solvent participation involving a polymeric strip of plumbate(II) oligomer as a key intermediate. A significant finding includes quick decomposition of perovskite crystal upon exposure to DMSO or DMF at room temperature, where the solvent molecules act as a base to remove acidic ammonium iodide from the perovskite crystal. This observation accounts for the difficulty in controlling perovskite solar cell fabrication. Overall, the polar solvent is indispensible first to degrade a 2-D sheet of crystals of lead(II) iodide into 1-D fibrous intermediates and then to promote Oswald ripening of perovskite crystals. The detailed chemical information provided here will help to rationalize the photovoltaic device studies that have so far remained empirical and to open a new venue to a developing field of microscale lead perovskite devices, as illustrated by fabrication of photovoltaic devices and photodetectors.

Fundamental understanding of how crystals of organic molecules nucleate on a surface remains limited because of the difficulty of probing rare events at the molecular scale. Here we show that single-molecule templates on the surface of carbon nanohorns can nucleate the crystallization of two organic compounds from a supersaturated solution by mediating the formation of disordered and mobile molecular nanoclusters on the templates. Single-molecule real-time transmission electron microscopy indicates that each nanocluster consists of a maximum of approximately 15 molecules, that there are fewer nanoclusters than crystals in solution, and that in the absence of templates physisorption, but not crystal formation, occurs. Our findings suggest that template-induced heterogeneous nucleation mechanistically resembles two-step homogeneous nucleation.

COMMUNICATIONThis journal is COMMUNICATION This journal is Table 1. Details of the photovoltaic performance of the solar cells using different HTLs, and the conductivity and HOMO level of different HTL films. a P3HT dissolved in 1 ml of chlorobenzene, b Li-TFSI dissolved in 6.8 µl of acetonitrile, c 10.2 µl D-TBP was added to the P3HT:Li-TFSI mixture solution, d The HOMO level was estimated from photoelectron yield spectroscopy analysis. A table of contents entryA 99.5% void-free perovskite layer with doped-P3HT hole-transporting layer showed highest PCE among the P3HT based hybrid solar cells.

Crystallization is the process of atoms or molecules forming an organized solid via nucleation and growth. Being intrinsically stochastic, the research at an atomistic level has been a huge experimental challenge. We report herein in situ detection of a crystal nucleus forming during nucleation/growth of a NaCl nanocrystal, as video recorded in the interior of a vibrating conical carbon nanotube at 20−40 ms frame −1 with localization precision of <0.1 nm. We saw NaCl units assembled to form a cluster fluctuating between featureless and semiordered states, which suddenly formed a crystal. Subsequent crystal growth at 298 K and shrinkage at 473 K took place also in a stochastic manner. Productive contributions of the graphitic surface and its mechanical vibration have been experimentally indicated.

Twenty potassium complexes of penta-[(4-substituted)phenyl][60]fullerene anions were synthesized and examined for their ability to form bilayer vesicles in water. The 4-substituents include alkyl groups ranging from methyl to icosanyl groups and perfluoromethyl, perfluorobutyl, and perfluorooctyl groups. The overall structure of the amphiphiles can be described as a nonpolar/polar/nonpolar (n-p-n') motif as opposed to the usual polar/nonpolar motif of lipid amphiphiles. Despite the hydrophobicity of the fullerene moiety (n-part) and alkyl/perfluoroalkyl chains (n'-part), all compounds except for the one with perfluoromethyl groups were soluble in water because of the centrally located fullerene cyclopentadienide (p-part) and spontaneously formed a vesicle of 25- to 60-nm diameter with a narrow unimodal size distribution. The vesicles are stable upon heating to 90 °C or standing over one year in air, as well as on a solid substrate in air or in vacuum, maintaining their spherical form. The vesicle membrane consists of an interdigitated bilayer of the amphiphile molecules, in which the fullerene n-part is inside and the n'-side is exposed to water. These vesicles, in particular the one bearing icosanyl chains, exhibit the smallest water permeability coefficient ever found for a self-assembled membrane in water.

Chemical reactions in solution almost always take place via a series of minute intermediates that are often in rapid equilibrium with each other, and hence hardly characterizable at the level of atomistic molecular structures. We found that single-molecule atomic-resolution real-time electron microscopic (SMART-EM) video imaging provides a unique methodology for capturing and analyzing the minute reaction intermediates, as illustrated here for single prenucleation clusters (PNCs) in the reaction mixture of metal–organic frameworks (MOFs). Specifically, we found two different types of PNCs are involved in the formation of MOF-2 and MOF-5 from a mixture of zinc nitrate and benzene dicarboxylates at 95 °C and 120 °C, respectively. SMART-EM identified a small amount of 1-nm-sized cube and cube-like PNCs in the MOF-5 synthesis, but not in the MOF-2 synthesis. In the latter, we instead found only linear and square PNCs, suggesting that the MOF-2/-5 bifurcation takes place at the PNC stage.

Modern transition state theory states that the statistical behavior of a chemical reaction is the sum of individual chemical events that occur randomly. Statistical analysis of each event for individual molecules in a three-dimensional space however is practically impossible. We report here that kinetics and mechanisms of chemical reactions can be investigated by using a one-dimensional system where reaction events can be observed in situ and counted one by one using variable-temperature (VT) atomic-resolution transmission electron microscopy (TEM). We thereby provide direct proof that the ensemble behavior of random events conforms to the Rice-Ramsperger-Kassel-Marcus theory, as illustrated for [2 + 2] cycloaddition of C molecules in carbon nanotubes (CNTs). This method gives kinetic and structural information for different types of reactions occurring simultaneously in the microscopic view field, suggesting that the VT-TEM opens a new dimension of chemical kinetics research on molecules and their assemblies in their excited and ionized states. The study carried out at 393-493 K showed that pristine CNT primarily acts as a singlet sensitizer of the cycloaddition reaction that takes place with an activation energy of 33.5 ± 6.8 kJ/mol. On the other hand, CNT suffers electron damage of the conjugated system at 103-203 K and promotes a reactive radical cation path that takes place with an activation energy of only 1.9 ± 0.7 kJ/mol. The pre-exponential factor of the Arrhenius plot gave us further mechanistic insights.

One-dimensional (1D) coordination polymers (CPs) experiences limitations in exfoliation into individual strands, which hamper their utility as functional 1D nanomaterials. Here we synthesize chiral 1D-CPs that feature the bis(dipyrrinato)zinc(II) complex motif. They can be exfoliated into single strands upon sonication in organic media, retaining lengths of up to 3.19 μm (ca. 2600 monomer units). Their chiroptical structure allows the exfoliated wires to show circularly polarized luminescence at an intensity 5.9 times that of reference monomer complexes.