Studies on Aromatic Trichromophore Systems Incorporating Anthracene Moieties. III. Crystal Structures of 2-(9-Anthryl)-1-(9-anthrylmethyl)ethyl 2-(9-Anthryl)ethyl Succinate (A₂A) and 2-(9-Anthryl)ethyl Acetate (AM) and Their Fluorescence in the Solid State

Abstract

The structures of 2-(9-anthryl)-1-(9-anthrylmethyl)ethyl 2-(9 anthryl )ethyl succinate (A2A) and 2-(9-anthryl)ethyl acetate (AM) have been determined by X-ray diffraction, and the molecular fluorescence of the crystals has been established. The A₂A crystal is triclinic while the AM crystal is monoclinic. A2A: Pī , a 18.514(5), b 11.802(3), c 10.836(3) Ǻ; α 99.63(2), β 85.75(2), γ 79.67(2)°, R 0.053 for 3547 observed reflections. AM: P2₁/c, a 12.566(2), b 12.991(2), c 8.805(2) Ǻ, β 97.84(1)°, R 0.040 for 1519 observed reflections. For the A₂A molecule as for the previously studied A₂PHEN and A₂SC (see Part II), the bisanthracene moiety and a large part of the ester chain show similar conformations. The crystal cohesion is due to numerous van der Waals interactions in both compounds and to π intermolecular overlap between the anthracene moieties of neighbouring molecules of AM. The fluorescence emission of the AM crystal is of excimer type and correlates with the intermolecular stacking of the anthracene rings. In contrast, the emission from the A₂A crystal was found to be very weak and with some similarity with the emission of the dilute solution. This is probably due to defects, not accounted for by the X-ray determination, permitting intramolecular interactions in the solid.