Alkylene-Chain Effect on Microwire Growth and Crystal Packing of π-Moieties

We developed a facile approach to modulate molecular arrangement through dimerizing of pi-moieties and tuning alkylene-bridge length. Dimers of fluoranthene-fused imide (DFAI-Cns) with various lengths of alkylene chains were synthesized by a Diels-Alder reaction followed by decarbonylation. DFAI-C3 and DFAI-C5 with odd-carbon alkylene chains display stronger one-dimensional growing tendency and better crystallinity than those with even-carbon alkylene chains. Microwires of dimers with odd-carbon alkylene chains were successfully obtained, and their molecular packing was analyzed by transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). Systematic investigation of their single crystal packing showed that alkylene chains with different lengths produced two kinds of molecular configurations. The V-shaped molecular configuration was observed from DFAI-C3 and DFAI-C5 with odd-carbon alkylene chains; however, the Z-shaped one was observed from DFAI-C4, DFAI-C6, and DFAI-C12 with even-carbon alkylene chains. Accordingly, we attributed the diverse microstructures and crystallinity of the dimers to their distinct molecular configurations in single crystals. In addition, a computational method was employed to demonstrate the weak intermolecular interactions in these dimers. Our investigation indicates that the introduction of bridging alkylene chains is an effective approach to modulate microwire growth and crystal packing of pi-systems in solid state.