Self-Organization, Optical, and Electrical Properties of α-Quinquethiophene-Dinucleotide Conjugates

Biodriven self-organization of α-quinquethiophene (t5): Cast films of 5′TA3′-t5 are electroactive, photoluminescent, and chiral. Their growth is not directed by intermolecular Watson–Crick hydrogen bonding between the A⋅⋅⋅T moieties of interacting molecules, but is governed by intra- and intermolecular thiophene–nucleobase stacking interactions. The synthesis and properties of 5′TA3′-t5 (8 a) and 5′CG3′-t5 (8 b) conjugates, in which the self-complementary dinucleotides TA and CG are covalently bound to the central ring of α-quinquethiophene (t5), are described. According to molecular mechanics calculations, the preferred conformation of both 8 a and 8 b is that with the dinucleotide folded over the planar t5 backbone, with the nucleobases facing t5 at stacking distance. The calculations show that the aggregation process of 8 a and 8 b is driven by a mix of nucleobase-thiophene interactions, hydrogen bonding between nucleobases (non Watson–Crick (W&C) in TA, and W&C in CG), van der Waals, and electrostatic interactions. While 8 b is scarcely soluble in any solvents, 8 a is soluble in water, indicating that the aggregates of the former are more stable than those of the latter. Microfluidic-induced self-assembly studies of 8 a showed the formation of lamellar, spherulitic, and dendritic supramolecular structures, depending on the concentration and solvent evaporation time. The self-assembled structures displayed micrometer dimensions in the xy plane of the substrate and nanometer dimensions in the z direction. Spatially resolved confocal microscopy and spectroscopy showed that the aggregates were characterized by intense fluorescence emission. Cast films of 8 a from water solutions showed chirality transfer from the dinucleotide to t5. The hole mobility of the cast films of 8 a was estimated using a two-electrode device under high vacuum and found to be up to two orders of magnitude greater than those previously measured for dinucleotide–quarterthiophene conjugates under the same experimental conditions.