Recent research on π-conjugated polymers has been shifting towards their practical applications in flexible organic devices, which requires more focus on their mechanical compliance (i.e. low stiffness and high ductility). Here we present a series of alkyl-substituted indacenodithiophene (IDT)-based donor-acceptor π-conjugated polymers. In these polymers, the acceptor unit was varied to tune the backbone conformation and intramolecular charge transfer (ICT), revealed by density functional theory (DFT) calculations. The polymers were synthesized via economically efficient direct arylation polycondensation (DArP). Their mechanical properties and charge mobilities were studied and correlated to their optoelectronic and thermal properties and thin film microstructures, investigated by ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopies, differential scanning calorimetry (DSC), X-ray diffraction (XRD) measurements, respectively. It was surprising to note that one of the polymer (PIDTBPD) exhibited a zigzag backbone conformation and strong ICT, which led to a high intrinsic ductility of this polymer. It showed similar stiffness (elastic modulus (Ef) = ca. 330 MPa) but significantly greater ductility (crack-onset strain (CoS) = ca. 40%) compared to most donor-acceptor π-conjugated polymers (Ef &gt; 300 MPa and CoS &lt; 15%). Charge carrier mobility measured using organic field-effect transistors (OFETs) demonstrated a value of 2×10-3 cm2V-1s-1 with a current on/off ratio of 2.5×106. This study provided useful insight into the design of π-conjugated polymers with mechanical compliance for stretchable organic electronics.

Indacenodithiophene-based semiconducting polymers for stretchable organic electronics

254th National Meeting (2017)

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