Formation of Cocrystal Nanorods by Solid-State Reaction of Tetracyanobenzene in 9-Methylanthracene Molecular Crystal Nanorods

Abstract

The reaction of single-component molecular crystal nanorods with a second species to form cocrystal nanorods is described. Single-component crystalline nanorods, composed of 9-methylanthracene (9-MA), are grown in a porous anodic aluminum oxide template. These templated rods are then exposed to a suspension of 1,2,4,5-tetracyanobenzene (TCNB) in water, which slowly diffuses into the 9-MA rods over the course of days. The two species form a 1:1 charge-transfer complex within the rods, which are transformed from crystalline 9-MA into cocrystalline 9-MA/TCNB. The cocrystal nanorods are characterized by electron microscopy, X-ray diffraction, and optical spectroscopy, confirming their highly crystalline structure and the formation of the charge-transfer complex. Attempts to grow cocrystal nanorods directly from a mixed solution were unsuccessful, as were attempts to recreate the single crystal-to-crystal reaction in macroscopic crystals. This work demonstrates how organic nanostructures can support structure-preserving chemical transformations that are impossible in larger crystals.

Micro‐/Nanostructured Multicomponent Molecular Materials: Design, Assembly, and Functionality

“…For example, the maximum positions of the excitation and emission spectra of pristine 9‐MA 1D nanorods are located at around 420 and 500 nm, respectively (Figure 13 a). 31 These values are consistent with those for the macro‐sized 9‐MA crystals, which excludes the possibility of any size and dimensional effects on the emissive properties. In contrast, for the nanococrystals of 9‐MA ⋅ TCNB, a new excitation peak appears at around 520 nm, and the fluorescence peak is shifted to 610 nm, which corresponds to a red‐emissive nanorod (Figure 13 b).…”

“…For example, Bardeen et al. have demonstrated that the reaction of single‐component 9‐methylanthracene (9‐MA) molecular crystal nanorods with a coformer (1,2,4,5‐tetracyanobenzene (TCNB)) in solution can afford new cocrystal nanorods 31. Firstly, 9‐MA nanorods were fabricated in a porous anodic aluminum oxide template.…”

“…b) Excitation and emission spectra of the 9‐MA ⋅ TCNB cocrystal nanorods. Inset: a single 200 nm diameter cocrystal nanorod excited with 365 nm (upper inset), and excited with 500 nm (lower inset) 31. Reproduced with permission from reference 31.…”

Fabrication of One‐Dimensional Organic Nanostructures Using Anodic Aluminum Oxide Templates

“…The charge-transfer nanorods were single crystals as confirmed by TEM and ED experiments. A similar diffusion experiment on microns-sized single crystal of 9-MA resulted in disintegration of that crystal and formation of the polycrystalline CT complex [65].…”

Thin films of a ferroelectric phenazine/chloranilic acid organic cocrystal

“…For example, the vapor pressures of the Phz and H 2 ca above the cocrystal, the individual vapor pressures of Phz and H 2 ca, and the phase diagram of the Phz-H 2 ca two-component system are not yet reported. This limitation has been overcome in the growth of other similar cocrystal compounds, for example using a solid-state reaction to convert single crystals of a single component to the phase [10]. Here we report a complementary approach that forms thin films of the desired phase using the fundamental concept that the fluxes of the two components need not be equal during growth.…”