Enantiodifferentiating Photodimerization of a 2,6‐Disubstituted Anthracene Assisted by Supramolecular Double‐Helix Formation with Chiral Amines

Abstract

A novel 2,6‐anthrylene‐linked bis(m‐terphenylcarboxylic acid) strand (1) self‐associates into a racemic double‐helix. In the presence of chiral mono‐ and diamines, either a right‐ or left‐handed double‐helix was predominantly induced by chiral amines sandwiched between the carboxylic acid strands with accompanying stacking of the two prochiral anthracene linker units in an enantiotopic face‐selective way, as revealed by circular dichroism and NMR spectral analyses. The photoirradiation of the optically active double helices complexed with chiral amines proceeded in a diastereo‐ (anti or syn) and enantiodifferentiating way to afford the chiral anti‐photodimer with up to 98 % enantiomeric excess when (R)‐phenylethylamine was used as a chiral double‐helix inducer. The resulting optically active anti‐photodimer can recognize the chirality of amines and diastereoselectively complex with chiral amines.

Chiroptical Properties of Symmetric Double, Triple, and Multiple Helicenes

“…On the other hand, the dipole transition moments of the B-type transitions are orthogonal to z , leading to a polarization in the xy -plane. Such symmetry considerations are fully confirmed by the ab initio calculations with electronic correlations (Figure , bottom) and are useful in assigning the relevant transitions. The convergent behavior of the physicochemical and chiroptical properties of [ n ]­helicenes has already been described, , and essentially the same symmetry argument should be extendable to higher helicene homologues with some appropriate modifications.…”

“…A more detailed explanation and discussion of these assignments can be found in the literature. , The symmetry of these states has been confirmed experimentally by polarized excitation measurements ,− and by computational investigations at various levels of the theory. ,− Among several transitions in the CD spectrum, the lowest-energy S 0 –S 1 transition is of primary interest as this often relates to the CPL band, which generally corresponds to the opposite S 1 to S 0 transition. While the bands in the high energy region typically consist of multiple transitions, the lowest-energy S 0 –S 1 transition is readily assignable and is subjected to various theoretical investigations. ,− The state symmetry relevant to the fluorescence and CPL bands in [6]­helicene is that of the corresponding lowest-energy transition, i.e., the B symmetry. Note that the symmetry of the lowest-energy transition is known to be reversed between even- and odd-numbered helicenes .…”

Supramolecular-induced regiocontrol over the photochemical [4 + 4] cyclodimerization of NHC- or azole-substituted anthracenes

“…6–11 Although the photochemical [4 + 4] cycloaddition of anthracene derivatives is one of the well-studied subjects in photochemistry, 12–19 relatively few studies deal with the photodimerization of 2,6-difunctionalized anthracenes. 20 Generally, irradiation of 2,6-difunctionalized anthracene derivatives ( AD ) in solution leads to the formation of two [4 + 4] photodimerization products, the anti - dAD (mixture of enantiomers) and syn - dAD (achiral) photodimers (Fig. 1a).…”

Near perfect head-to-head selectivity on the supramolecular photocyclodimerisation of 2-anthracenecarboxylate with self-organised gemini surfactant bilayers

“…Ever since the first report in 1867, [1][2][3] the [4+4] photocyclodimerisation of anthracene and its derivatives has attracted much attention due to the unique structure and properties of the photocyclodimers obtained, and has been employed indeed as a key motif in energy storage and photoreversible devices. [4][5][6][7][8] However, controlling regioand enantioselectivities of the photocyclodimerisation of anthracene derivatives, such as 2-anthracenecarboxylate (AC) (Scheme 1), is a challenge, which has driven researchers to the use of supramolecular approach, 9,10 using cyclodextrins, [11][12][13][14] proteins, 15,16 molecular templates, [17][18][19][20][21] molecular cages, [20][21][22] twisted self-associated templates, 18 organogels, 23 and helical metal nanostructures 24 as hosts and templates. Most of the reported systems, however, require the multi-step synthesis of host/template, the modification of guest substrate and/or the irradiation in organic media at low temperature.…”