Identification of an Overlooked Halogen‐Bond Synthon and Its Application in Designing Fluorescent Materials

Abstract

Research on new supramolecular synthons facilitates the progress of materials design. Herein, the ability of sp2 carbonyl oxygen atoms to act as halogen‐bond acceptors was established through cocrystallization. Four sets of carbonyl compounds, including aldehydes, ketones, esters, and amides, were selected as halogen‐bond acceptors. In the absence of strong hydrogen bonds, 14 out of 16 combinations of halogen‐bond donors and acceptors could form cocrystals, whereby the supramolecular synthon C=O⋅⋅⋅X acts as the main interaction. Further, the geometric parameters of the C=O⋅⋅⋅X interaction were statistically revealed on the basis of the crystallographic database. The bifurcated interaction mode that has been observed in other halogen‐bond synthons rarely occurs in the case of C=O⋅⋅⋅X. The robustness of C=O⋅⋅⋅X makes its application in crystal engineering possible and opens up new opportunities in designing multicomponent fluorescent materials, as indicated by multicolor emission of cocrystals D through C=O⋅⋅⋅X interactions.

One-Pot Route to X-perfluoroarenes (X = Br, I) Based on FeIII-Assisted C–F Functionalization and Utilization of These Arenes as Building Blocks for Crystal Engineering Involving Halogen Bonding

“…Until now, the most common synthons for these purposes were based on linear XB/XB-bifunctional species (X = Br, I) such as two-center dihalides X 2 , − di-X-perfluoroarenes, ,− XCCX, − or bent XB/XB synthons such as haloalkanes. − Cocrystallization of all these XB/XB-donating building blocks with appropriate bifunctional XB/XB acceptors in many reported instances leads to well-organized supramolecular networks. Apart from their application in crystal engineering, mono- and di-X-perfluoroarenes (X = Br, I) have been used in the modulation of photophysical − properties, stabilization of explosives, gels, micelles, nanowire preparation, and so on.…”

Recent Developments in Polymeric Assemblies and Functional Materials by Halogen Bonding

“…Co‐assembly of luminescent π‐scaffolds with appropriate halogen bonding partners offers an opportunity to regulate their fluorescence color to a great extent. For example, fluorescent properties of a napthalane derivative with an aldehyde functionality could be drastically changed from blue to yellow by co‐crystallization with DITFB , which was attributed to the C−I⋅⋅⋅O=C halogen bonded co‐assembly [91] . In recent years, halogen bonding has emerged as a successful tool for designing metal‐free self‐assembled organic materials for efficient room temperature phosphorescence (RTP) [92] .…”

Conservation of the Hydrogen-Bonded Pyridone Homosynthon in Halogen-Bonded Cocrystals

“…The carbonyl oxygen has also been demonstrated to be a viable halogen bond (XB) acceptor, albeit weaker and less reliable than sp 2 nitrogen. − The question therefore arises whether a combination of pyridone and appropriate halogen bond donors would lead to structures in which the pyridone homosynthon is retained (Scheme d) or the introduction of a halogen bond donor would disrupt the pyridone homosynthon, possibly even stabilizing the hydroxypyridine tautomer via an X···N­(sp 2 ) halogen bond.…”