Synthesis and Supramolecular Properties of Molecular Clips with Anthracene Sidewalls

Abstract

Novel molecular clips with anthracene sidewalls (1 a-c) were synthesized; they form stable host-guest complexes with a variety of electron-deficient aromatic and quinoid molecules. According to single-crystal structure analyses of clip 1 c and 1,2,4,5-tetracyanobenzene (TCNB) complex 14@1 b, the clips' anthracene sidewalls have to be compressed substantially during the complex formation to provide attractive pi-pi interactions between the aromatic guest molecule and the two anthracene sidewalls in the complex. The compression and expansion of aromatic sidewalls are calculated by molecular mechanics to be low-energy processes, so the energy required for compression of the anthracene sidewalls during complex formation is apparently overcompensated by the gain in energy resulting from the attractive pi-pi interactions. The finding that complexes of the clips 1 a-c are more stable than those of the corresponding clips 2 a-c can be explained in terms of the larger van der Waals contact surfaces of the anthracene sidewalls in 1 a-c (relative to the naphthalene sidewalls in 2 a-c). Color changes resulting from charge-transfer (CT) bands are observed in complex formation by 1 a-c: from colorless to red or purple with TCNB (14), and from yellow to green with 2,4,7-trinitro-9-fluorenone TNF (17). Independently, the host 1 b and guest 14 fluoresce from their respective excited singlet states, whilst in the complex 14@1 b the charge-transfer state quenches the higher-energy singlet states of the two components, and as a result luminescence is only observed from this new CT state. To the best of our knowledge, complex 14@1 b is the first example of CT luminescence from a host-guest complex. The binding constant determined for the formation of the TCNB complex 14@1 b from a UV/Vis titration experiment (Ka = 12 400 m(-1)) agrees well with the value (K(a) = 12 800 m(-1)) obtained by 1H NMR titration.

A Versatile Bis‐Porphyrin Tweezer Host for the Assembly of Noncovalent Photoactive Architectures: A Photophysical Characterization of the Tweezers and Their Association with Porphyrins and Other Guests

“…Though 1 is rather rigid, a larger aperture of the bite could be achieved by multiple small‐angle distortions in the structure of the bis‐porphyrin tweezers, which could be affordable with low‐energy costs. Recently, force‐field calculations have shown that compression and expansion of the side‐walls in a molecular clip with anthracene side‐walls are low‐energy processes 22. The energy necessary for the expansion can be compensated by the formation of new bonds in the host–guest complex.…”

The First Centrohexaindane Bearing Twelve Functional Groups at Its Outer Molecular Periphery and Related Lower Veratrole‐Derived Centropolyindanes

“…Due to the presence of the peripheral methoxy groups, the electrophilicity of the triketone should be markedly reduced as compared to the parent triptindanetrione, which was found to undergo threefold addition of nucleophiles, such as phenyllithium and methyl-and benzylmagnesium bromide. [5,23,28,31] In the present case, the addition of three veratryl residues to the triketone 15 was carried out by use of 4-veratrylmagnesium bromide, prepared from 4-bromoveratrole (16) ·+ at m/z = 774 and m/z = 912, respectively). Similarly rapid, and highly stereospecific, loss of water is known for other preoriented bridgehead-hydroxylated centropolyindanes and simpler cyclic alcohols.…”

Supramolecular Species Bearing Quaternary Azaaromatic Moieties

“…82 Complexes of clips (65) are weaker than those of clips (66), since 66 have larger van der Waals contact surfaces of the anthracene sidewalls as compared with naphthalene sidewalls of 65. 82 Complexes of clips (65) are weaker than those of clips (66), since 66 have larger van der Waals contact surfaces of the anthracene sidewalls as compared with naphthalene sidewalls of 65.…”