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An exceptionally large size cuboctahedral imine cage is obtained from small size organic molecules in a thermodynamically driven [8+12] cyclocondensation. This is a demonstration of the role of entropy of symmetry as a driving force in reversible reactions.

Trianglamines, macrocyclic heteraphanes, were readily synthesised through a [3+3] cyclocondensation of (R,R)-1,2-diaminocyclohexane with terephthalaldehyde, followed by NaBH4 reduction and N-alkylation. The macrocyclic ring shows a remarkable ability to change its conformation, as a consequence of rotation about the C-N bonds or nitrogen inversion due to protonation or N-alkylation, as revealed by circular dichroism spectra, computational modelling and X-ray diffraction analysis. The flexible natures of the trianglamine macrocycles allow ready accommodation of a variety of guest molecules to form crystalline inclusion complexes of highly diversified interpenetrating structures.

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The electronically excited states of the phthalimide chromophore have been studied by means of linear dichroism (LD) of samples partially oriented in poly(vinyl alcohol) films, magnetic circular dichroism (MCD), and circular dichroism (CD) spectroscopy. On the basis of the LD measurements, the low-energy tail (340−320 nm) of the first absorption band is assigned to an out-of-plane polarized n→π* transition (I). At higher energy, the electronic spectrum is resolved into contributions from five π→π* transitions:  II (300 nm, long-axis polarized), III (275 nm, short-axis polarized), IV (235 nm, short-axis polarized), V (220 nm, long-axis polarized), and VI (∼210 nm, short-axis polarized). The results from semiempirical (INDO/S-CI) and ab initio (CIS/6-31+G(d)) MO calculations compare well with the proposed assignments of the excited states. Degenerate exciton interaction between electric-dipole-allowed transitions of two phthalimide chromophores is observed in the electronic absorption spectra of the achiral bis-phthalimides 2a−c and in the CD spectrum of the chiral bis-phthalimide 3a. For the latter compound, the solid-state geometry has been determined by X-ray diffraction analysis. Good agreement between experimental and computed CD spectra confirms that the coupled-oscillator exciton model provides the basis for a reliable nonempirical method for the assignment of absolute configuration for this class of compounds. Nondegenerate exciton coupling between phthalimide and benzoate or phenyl chromophores is born out in the CD spectra of homochiral molecules 3c and 3d with the rigid cyclohexane skeleton. Finally, the exciton coupling method is used to make stereochemical assignments for the acyclic, conformationally flexible derivatives 4a−c and 5b.

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