Synthesis, structure, and contrasting chiroptical properties of large trianglimine macrocycles

Abstract

We have synthesized a number of large trianglimine macrocycles (3a-3f) using our methodology of (3+3) cyclocondensation of (R,R)-trans-1,2-diaminocyclohexane (1) with rigid aromatic dialdehydes (2a-2f), having benzene, biphenyl, terphenyl, styrene, or divinylbenzene spacers. The structures of these chiral macrocycles have been analyzed using computational methods as well as CD spectroscopy. Whereas trianglimines 3a-3d gave uniformly negative exciton Cotton effects, as expected, styrene- and divinylbenzene-based trianglimines 3e and 3f gave opposite-sign exciton Cotton effects. Their contrasting CD behavior was traced by computational methods to subtle differences in the relative orientation of the electric dipole transition moments in the chromophores of the trianglimines. The presence of low-intensity long-wavelength electronic transitions having large rotational strengths in the electronic spectra of 3e and 3f can be accounted for by the symmetry properties of the trichromophoric macrocycles.