MOLECULAR AND CRYSTAL STRUCTURES OF DONOR - ACCEPTOR SUBSTITUTED POLYENES INVOLVING 1,3-INDANDIONE AND DIBENZOCYCLOHEPTENEDIONE MOIETIES. Vladimir Khodorkovsky¹, Arkady Ellern, Ben-Gurion University of the Negev, Chemistry Dept., P.O.B. 653, Beer Sheva, Israel.

Donor-acceptor substituted polyenes present currently a subject of numerous investigations due to their nonlinear optical properties. The importance of specific structural features in such chromophores for efficient second harmonics generation has been established, in particular, within the frame of bond length alternation (BLA) approach.

Derivatives involving the electron accepting moiety of 1,3-indandione and its structural analogs are often photoconducting and possess moderate to strong nonlinear optical properties. Many derivatives are distinguished by their ability to form several polymorphic modifications. For instance, for 2-(p-dimethylaminobenzylidene)-1,3-indandione, yellow-orange in solutions, two red and one blue polymorphs are known.

Recently we have synthesized a series of 2-ylidene 1,3-indandione and dibenzocycloheptenedione derivatives and determined their crystal structures. The deep color in solid state apparently can not be explained by enhanced intermolecular interactions and no considerable difference in BLA patterns has been found. The results of our crystallographic and quantum mechanical calculations which can explain the tendency for polymorphism and deep color in solid state within this class of compounds will be presented.

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1. This work was supported by the Ministry of Science and Art, Israel.