Synthesis and characterization of amino-capped oligothiophene-based hole-transport materials

A series of seven thiophene-based oligomers were prepared as hole transport materials. The DBATn series is composed of six oligothiophenes (n = 1-6) capped with two dibutylaminostyryl electron donating moieties. The band gaps for these compounds range from 2.47 to 2.19 eV. It was found that the bis(amino) substituents control the ionization potential, while the electron affinity and energy gap depend directly on the oligothiophene chain length. The bulk crystalline properties of these materials depend strongly on whether the number of thiophene rings in the bridge is even or odd. This results in the compounds that have an odd number of thiophene units in the bridge to exhibit depressed melting points with respect to the structures with an even number of rings. X-Ray structure determination was obtained from single crystals of DBAT1 and -2. Good solubility, thermal stability and film forming properties were found throughout the series of compounds. A seventh compound, DH2E4T, was also prepared. This molecule is comparable to alpha,omega-dihexylsexithiophene but with greater solubility and reduced optical band gap (2.32 eV).