Oligothiophenes end-capped by nitriles. Preparation and crystal structures of alpha,omega-dicyanooligothiophenes NC(C4H2S)(n)CN (n=3-6)

by Barclay, Tosha Madeva; Cordes, A. Wallace; Mackinnon, Craig D.; Oakley, Richard T.; Reed, Robert W.

The synthesis of dicyanooligothiophenes NC(C4H2S)(n)CN (n = 3-6) is reported. For it = 3, 4, and 5 the dinitriles are generated by treatment of the corresponding dibromo compounds with copper(I) cyanide in quinoline. For n = 6 the preparation involves the Ni-catalyzed coupling of 5-bromo-2,2':5',2 ''-terthiophene-5 ''-carbonitrile. The structures of all four dicyano derivatives have been determined by X-ray crystallography. For n = 3, the space group is monoclinic C2/c, with a = 18.363(7), b = 11.8356(9), c = 30.666(4) Angstrom, beta = 102.15(2)degrees, V = 6515(3) Angstrom(3), Z = 20. For n = 4 the space group is triclinic P (1) over bar, a = 7.3254(9), b = 7.8658(6), c = 8.1813(8) Angstrom, alpha = 64.706(8), beta = 76.059(8), gamma = 76.692(8)degrees, V = 409.29(7) Angstrom(3), Z = 1. For n = 5 the space group is monoclinic C2/c, with a = 13.633(4), b = 11.706(5), c = 37.073(8) Angstrom, beta = 90.22(2)degrees, V = 5929(3) Angstrom(3), Z = 12. For n = 6, the space group is monoclinic P2(1)/a, with a = 13.8962(14), b = 5.9100(16), c = 14.0798(16) Angstrom, beta = 98.446(4)degrees, V = 1143.8(4) Angstrom(3), Z = 2. In all four structures the molecules are approximately planar, with all-trans thiophene rings. The oligomers are linked into ribbonlike arrays by intermolecular CN---H contacts. For n = 3, 4, and 5 these ribbons are stacked in approximately coplanar layers (pi-stacks). For n = 6 the ribbons are packed in a herringbone motif very similar to that observed in H(C4H2S)(6)H(alpha-6T). The UV-visible spectra of NC(C4H2S)(n)CN (n = 2-6) have been recorded, and shifts in the pi-pi* excitation energies of these compounds relative to those found in other alpha,omega-disubstituted oligothiophenes are interpreted in the light of MNDO calculations. Extended Huckel band structure calculations on NC(C4H2S)(n)CN (n = 4 and 6) indicate substantial intermolecular interactions; both structures have well-developed 2-dimensional electronic structures.

Journal
Chemistry of Materials
Volume
9
Issue
4
Year
1997
Start Page
981
ISBN/ISSN
1520-5002; 0897-4756
DOI
10.1021/cm960545l