STRUCTURAL STUDY OF COMPOUNDS MODELING ELEMENTARY POLYMER UNITS .6. X-RAY STRUCTURAL AND QUANTUM-CHEMICAL INVESTIGATION OF THE CIS-ISOMERICAND TRANS-ISOMERIC MODELS OF THE POLYNAPHTHOYLENEBENZ-IMIDAZOLE ELEMENTARY UNITS

The X-ray structural investigation of the naphthoylenebis-(benzimidazo le) (1) cis- and trans- isomers as models for the cis and trans elemen tary units of the corresponding poly(naphthoylenebenzimidazoles) (PNBI ) was carried out. The correctness of the previous identification of t he isomers was confirmed, and exact geometrical parameters of the PNBI elementary units (required, in particular, for the calculation of the Kuhn segment of PNBI) were determined. Quantum-chemical semi-empirica l calculations of the ground and excited electronic states of the isom ers were carried out. Both experimental and theoretical data confirm a larger stability of the planar pi-conjugated structure of the trans-i somer in comparison with the cis-isomer in the ground as well as in th e excited electronic state. Crystals of the cis- and trans-isomers obt ained from trifluoroacetic acid solutions are the solvates of bis(trif luoroacetates) of diprotonated 1 with an extremely high content of the solvating trifluoroacetic acid. This peculiarity is favourable for mo delling the main characteristics of the interaction between PNBI and p rotonic polar solvent molecules, viz. preferred types of H-bonding and a possibility of interaction of the electronic lone pairs of the solv ent molecules with the pi-electronic systems of the elementary units o f PNBI by charge transfer complexes.