Reversible Photocapture of a [2]Rotaxane Harnessing a Barbiturate Template

• Published in: Journal of organic chemistry 2015-01, Vol.80 (2), p.988-996
• Main Authors: Tron, Arnaud, Thornton, Peter J, Lincheneau, Christophe, Desvergne, Jean-Pierre, Spencer, Neil, Tucker, James H. R, McClenaghan, Nathan D
• Format: Article
• Language: English
• Subjects: Anthracenes - chemistry; Magnetic Resonance Spectroscopy; Molecular Structure; Photochemical Processes; Rotaxanes - chemical synthesis; Rotaxanes - chemistry
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo502452t

Photoirradiation of a hydrogen-bonded molecular complex comprising acyclic components, namely, a stoppered thread (1) with a central barbiturate motif and an optimized doubly anthracene-terminated acyclic Hamilton-like receptor (2b), leads to an interlocked architecture, which was isolated and fully characterized. The sole isolated interlocked photoproduct (Φ = 0.06) is a [2]rotaxane, with the dimerized anthracenes assuming a head-to-tail geometry, as evidenced by NMR spectroscopy and consistent with molecular modeling (PM6). A different behavior was observed on irradiating homologous molecular complexes 1⊂2a, 1⊂2b, and 1⊂2c, where the spacers of 2a, 2b, and 2c incorporated 3, 6, and 9 methylene units, respectively. While no evidence of interlocked structure formation was observed following irradiation of 1⊂2a, a kinetically labile rotaxane was obtained on irradiating the complex 1⊂2c, and ring slippage was revealed. A more stable [2]rotaxane was formed on irradiating 1⊂2b, whose capture is found to be fully reversible upon heating, thereby resetting the system, with some fatigue (38%) after four irradiation–thermal reversion cycles.