Conformational analysis of oligothiophenes and oligo(thienyl)furans by use of a combined molecular dynamics/NMR spectroscopic protocol

The conformational analysis of oligothiophenes and oligo(thienyl)furans by use of a combined molecular dynamics (MD)/NMR spectroscopic protocol is described. A series of MD simulations were performed for 2-(2'-thienyl)-3-hexylthiophene (2), 2,5-bis(3'-hexyl-2'-thienyl)thiophene (3), 2,5-bis(4'-hexyl-2'-thienyl)thiophene (4), 2,5-bis(3'-hexyl-2'-thienyl)furan (5), and 2,5-bis(4'-hexyl-2'-thienyl)furan (6) with a new MM2 torsional parameter set developed earlier for unsubstituted and methyl-substituted 2,2'-bithiophene and 2-(2'-thienyl)furan systems. Conformationally averaged structures were determined for each of these molecules. Theoretical NOE buildup curves were then calculated for these averaged structures using a full matrix relaxation treatment and were compared to those obtained experimentally. Excellent agreement between the calculated and experimental NOE buildup curves was generally observed, in particular for the 2,2'-bithiophene systems.