J-like Aggregation of Azobenzene-Linked Amphiphile, C₆AzoC₅N⁺Br^-, in Single Crystal

Abstract

The crystal structure of an azobenzene-linked, single-chain ammonium amphiphile (C₆-AzoC₅N⁺Br^-), C₂₇H₄₂N₃O₃Br, was determined by X-ray diffraction. The crystal is triclinic with the space group P1, Z=2, a=2.7446(9), b=0.8592(1), c=0.6112(1)nm, α=106.91(2), β=87.05(2), and γ=93.18(4)°. The structure was solved by the direct method and r efined by the block-diagonal least-squares method to the R-value of O.060 for 3535 reflections (sinθ/λ<0.56). In contrast to other azobenzene derivatives, azobenzene part of the C₆-AzoC₅N⁺Br^- molecule has very good planarity. tortion angles between the azo moiety and the benzene rings are within 2°. The zigzag planes of the spacer alkyl and the tail alkyl parts are linked to the azobenzene plane with small tortion angles, O.1 and 6.3°, respectively. this shapes the whole molecule a long thin plate. The crystal structure consists of regularly stacking bimolecular layers along the α-direction in which azobenzene chromophores aggregate in the J-like (head-to-tail) fashion between adjacent molecules. The detailed, molecular and crystal structure of C₆AzoC₅N⁺Br^- is very similar to that of the previously analyzed homologous compound, C₁₂AzoC₅N⁺Br^-.