PHOTODIMER OF 9,10-DIMETHYLANTHRACENE AND TETRACENE - CRYSTAL AND MOLECULAR-STRUCTURE, PHOTOPHYSICS, AND PHOTOCHEMISTRY

The single-crystal X-ray analysis of the photodimer of 9.10-dimethylanthracene and tetracene is described. The dimer crystallizes in the monoclinic space group P21/c with four molecules per unit cell of dimensions a = 21.323 (8) Ȧ, b = 12.642 (4) Ȧ, c -8.587 (3) Ȧ, and β * 93.25 (2)°. The conventional K factor for the 2573 reflections of the terminal data set for which I/σ(l) <3.0 is 0.034. The bonds which are formed by the photodimerization [C(6)-C(26). 1.627 (2): C( 13)-C(37), 1.629 (2) A) are equal within experimental error. The molecular fluorescencc is quenched by a thermally activated process, identified as a transfer of electronic excitation energy from the naphthalene chromophore into the pair of benzene chromophores in the other part of the molccule, followed by immediate photodissociation. The product molecules appear in their electronically excited (exciplex) state. Rephotodimerization of the dissociated moleculesin the photodimer host crystal requires thermal activation. The polarization properties of the absorption and emission spectra of these dissociated molecules have been determined. © 1979, American Chemical Society. All rights reserved.