Acetylene-extended triarylamines for solution-processable p-channel OFETs

New acetylene-extended molecules were developed as a semiconducting layer for application in solution-processable organic field-effect transistors through coupling reactions using substituted triphenylamines as wings and diacetylene as spacer units. The influence of donor ability and spacer strength on the electrical properties was explored by developing different acetylene-extended triarylamines with D–π and D–π–π–D architectures and their structure–properties analysis. Their optical studies revealed narrow Stoke's shift and optical bandgap values, especially for highly electron-rich systems. Encouraging results supported by their electrochemical studies that revealed high HOMO energy levels ranging from –5.1 to –5.3 eV suggested a low energy barrier and good hole-transporting ability, hence, their applicability as p-channel OFETs. Furthermore, the extended conjugation in D–π–π–D based molecules relative to their corresponding D–π system caused enhanced molecular orbital overlap along the triphenylamine and facilitated good charge transport characteristics. Upon fabrication as the semiconducting channel in top-gate/bottom-contact OFET devices, the acetylene-extended D–π–π–D system showed good p-channel properties with hole mobilities up to 1.2 cm2/Vs and the highest on/off ratio of 107.