A research group at Mahidol University in Thailand has found that tosyl groups, previously seen as standard synthetic tools, can direct the creation and properties of pillararenes. These are pillar-shaped macrocyclic molecules common in supramolecular chemistry. The results, released in the Journal of the American Chemical Society, indicate that the groups function as an internal code affecting how molecular parts organize before bonds form and allowing temperature-based switching with visible color shifts.
Simulations of molecular dynamics and fragment orbital calculations show how this common synthetic group acts as built-in guidance for assembly and supports reversible color changes triggered by heat.
The work from teams at Mahidol University, Suranaree University of Technology in Thailand, and the University of Tsukuba in Japan reveals that tosyl groups enable molecules to prearrange into pseudorotaxane forms through specific interactions before covalent bonding. This leads to a preferred single product among eight possible outcomes in macrocyclization without external templates.
The tosyl group thus operates as a directing element in supramolecular processes rather than a neutral handle. After ring formation, the count of tosyl units controls higher-order assembly, described as supramolecular valency. One unit gives separate rings, four lead to dimers, and five produce extended interlocked chains. Brominated versions without the same interactions yield only random mixtures.
Oxidation of the tetratosylated ring adds a benzoquinone unit for responsive behavior. The molecule acts as a thermal topology switch, alternating between an interpenetrated dimer at lower temperatures and a self-included monomer at higher ones, with a color change from red to yellow detectable by smartphone.
Dynamics simulations verified the mechanism at atomic level, with arm folding into the cavity above 60 degrees Celsius. Orbital calculations confirmed interaction energies increase with more tosyl groups. The findings suggest such energies could be calculated in advance to design assembly outcomes.
Overall, the study points to a change in molecular design by viewing substituents as programmable features encoding selectivity and function from the start.
Publication: Araya Ruengsuk et al, Beyond Passive Substituents: Tosyl-Directed Self-Templation Enables Selective Pillar[4 + 1]arene Formation and Topology Switching, Journal of the American Chemical Society (2026). DOI: 10.1021/jacs.6c03673
