Abstract
Covalently linked π-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties. Here, we present the one-pot synthesis of two intramolecularly π-stacked dimers and disclose how intramolecular stacking modes dictate photoswitching properties. The dimer, which features cofacially stacked chromophores and geometrically favours intramolecular photochemical [2 + 2] cycloadditions, displays a nearly irreversible photoswitching behaviour. By contrast, the dimer, bearing crosswise stacked chromophores, is geometrically unfavourable for the cycloaddition and exhibits a highly reversible photoswitching process, in which the homolysis and reformation of carbon−carbon single bonds are involved. Moreover, the chiral carbon centres of both dimers endow these photoswitches with chirality and the separated enantiomers exhibit tuneable chiroptical properties by photoswitching. This work reveals that intramolecular stacking modes significantly influence the photochemical properties of π-stacked dimers and offers a design strategy toward chiral photoswitchable materials.
Highlights
Linked π-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties
The elongated C−C single bonds are accompanied by the decreasing of bond dissociation energies[13] and the increasing of reactivity, for instance, via thermal- or photo-activated bond cleavage[14,15]
All new compounds were characterized by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS)
Summary
Linked π-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties. Benefited from the well-defined alignments of the two πmoieties, geometrically preferred reactions, such as photoinduced cycloadditions, can be achieved efficiently[7,8,9] Another important character of these dimers is their high intramolecular steric repulsion, which may lead to unusually long carbon–carbon single bonds (bond length greater than 1.6 Å)[10,11,12]. The elongated C−C single bonds are accompanied by the decreasing of bond dissociation energies[13] and the increasing of reactivity, for instance, via thermal- or photo-activated bond cleavage[14,15] These remarkable structural features and their accompanying potential photochemical reactivity make covalently linked dimers promising candidates for photo-responsive materials. Transferring the chirality into a photoswitch enables the reversible and precise control over chiral information
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