No abstract

One important objective of molecular assembly research is to create highly complex functional chemical systems capable of responding, adapting, and evolving. Compared with living systems, the synthetic systems are still rather primitive and are far from realizing those features. Nature is by far the most important source of inspiration for designing and creating such systems. In this critical review, we summarize an alternative approach, inspired by catalysis, to examine and describe some molecular assembly processes. A new term, "catassembly," is suggested to refer to the increase in the rate and control of a molecular assembly process. This term combines the words "catalysis" and "assembly," and identifiably retains the Greek root "cat-" of catalysis. The corresponding verb is "catassemble" and the noun is "catassembler", referring to the "helper" species. Catassembly in molecular assembly is a concept that is analogous to catalysis in chemical synthesis. After using several examples to illustrate the characteristics of catassembly, we discuss future methodological and theoretical developments. We also emphasize the significance of the synergy between chemical synthesis and molecular assembly, especially for hierarchical assembly systems. Because most efforts in the field of molecular assembly have been devoted to the design and synthesis of molecular building blocks, we wish to stress the apparently missing yet critical link to complex chemical systems, i.e., the design and utilization of molecular catassemblers to facilitate the formation of functional molecular assemblies from building blocks with high efficiency and selectivity. This rational control and accelerated method will promote the systems chemistry approach, and may expand the spectrum of molecular assembly from basic science to applications.

One-dimensional channel materials as formed by some zeolites and mesoporous silicas are attractive hosts for the preparation and investigation of hierarchically organized inorganic-organic hybrid materials, presenting a successive ordering from the molecular up to the macroscopic scale. [1][2][3][4] We have been using zeolite L (ZL) as a host in most of our experiments. ZL crystals feature strictly parallel channels arranged in a hexagonal symmetry. The size and aspect ratio of the colorless crystallites can be tuned over a wide range. Their one-dimensional channels can be filled with suitable guests. Geometrical constraints imposed by the host structure lead to supramolecular organization of the guests in the channels. The supramolecular organization of dyes inside the ZL channels is the first stage of organization. It allows light harvesting within the volume of a dye-loaded ZL crystal and also allows radiationless energy transport to either the cylinder ends or to the center of the channel. One-dimensional excitation-energy transport has been observed in these guest-host materials.[5] The second stage of organization is the coupling of an external acceptor or donor stopcock fluorophore to the ends of the ZL channels, which can then trap or inject electronic excitation energy. The third stage of organization is achieved by interfacing the material to an external device through a stopcock intermediate. [1,3]

Two-dimensional (2D) circular shape nanostructures (e.g., "nano-coins") are ubiquitously present in thylakoids and grana within chloroplasts of plant cells in nature. The design and fabrication of 2D nano-coins with controlled sizes and thicknesses yet remain challenging tasks. Herein, we present a noncrystallization approach to achieve 2D nano-coins from assemblies of a set of zwitterionic giant surfactants. Distinguished from traditional crystallization approaches where the 2D nanostructures with specific crystallographic symmetries are fabricated, the noncrystallization assembly of giant surfactants results in 2D nano-coins that are derived from the separation of assembled 3D multiple lamellar cylindrical colloids with uniform diameters. The diameters and thicknesses of these nano-coins can be readily tailored by varying the molecular length of giant surfactants' tails. The formation of 2D nano-coins or 3D cylindrical colloid suprastructures is controlled by tuning the pH value of added selective solvents. This new strategy opens a door for controlling the shape, size, and size distribution of assembled nanostructures with different hierarchies.