Ronald Castellano, University of Florida, USA, talks to NJC about his latest work exploring the role of stereoelectronic interactions in determining the supramolecular assembled structure of simple piperidones.

How did you get interested in this research project? 

We have always been interested in molecular self-assembly, in particular understanding and developing new relationships between structure and emergent physical, chemical, or materials properties. Driving this interest, of course, is the powerful role that supramolecular strategies play, in areas ranging from defining biological structure and function to optimizing the efficiency of organic electronic devices. Several years ago we initiated a research program to explore whether favorable stereoelectronic interactions within molecules could influence their self-assembly and macromolecular behavior. As vehicles for these studies we chose cyclic beta-aminoketones, synthetically accessible and stable building blocks with well-defined interactions between donor and acceptor orbitals. We have since drawn relationships, using these systems, between molecular structure, macromolecular behavior, and electronic properties. 

What is the most important result in the paper? 

That molecular-level structural perturbations that arise from or otherwise influence through-bond donor-acceptor interactions have measurable consequences on supramolecular structure. Stereoelectronic interactions are most frequently discussed at the molecular level where they influence ionization potentials, bond lengths and angles, conformation or reactive intermediate stability, reaction stereoselectivity, etc. The system studied here has allowed us to (a) draw connections between molecular (conformation and shape) and supramolecular (solid-state assembly) structures and (b) quantify the interactions of interest through extensive first-principles calculations. 

What are the implications of the results you present in this paper? 

This work shows that, while stereoelectronic interactions are weak, they are significant and probably under-utilized in efforts that seek to control how molecules organize. Moreover, the interactions are featured in molecules that have shapes and dipoles that are useful for the construction of novel donor-acceptor materials. 

Are there any particular challenges facing future research in this area? 

One challenge is to understand how stereoelectronic interactions can be used to influence self-assembly events in solution. Along the same lines, there is little known about the "cooperativity" or "tunability" of these forces. Even so, there are significant synthetic and design opportunities associated with exploiting through-bond donor-acceptor interactions in the context of optoelectronic devices or modulating materials properties.