Thiophene-benzothiadiazole based donor-acceptor-donor (D-A-D) bolaamphiphiles, self-assembly and photophysical properties

Bolaamphiphilies with D-A-D type pi-conjugated rigid cores composed by thiophenes as donors (D) and benzothiadiazole (BTD) as central acceptor (A) have been synthesised. Their self-assemblies and photophysical properties were investigated by polarising optical microscope, differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. Such compounds can self-assemble into honeycomb cylinder mesophases with Col(hex) increment /p6mm and Col(squ)/p4mm lattices in their pure states as well as organogels with different morphologies in organic solvents. Their absorption spectra cover nearly the entire visible light range and their band gaps are relatively low. Tetrathiophene BTD based bolaamphilphiles (BT4/n) with higher D/A ratios than the bisthiophene BTD bolaamphilphiles (BT2/n) can self-assemble into more ordered nanostructures in both bulk states and solution. Both the absorption and emission peaks of BT4/n are strongly red shifted. The influence of the molecular conformation, the conjugated core length, as well as the D/A ratio on the self-assemble and photophysical characteristics of such D-A-D bolaamphiphiles are discussed.