Tuning the Semiconducting Behaviors of New Alternating Dithienyldiketopyrrolopyrrole–Azulene Conjugated Polymers by Varying the Linking Positions of Azulene

Three new conjugated polymers <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> with dithienyldiketopyrrolopyrrole (DPP) and azulene moieties were synthesized and characterized. The five-membered rings of azulene are connected with DPP in <b>DPPA1</b> and <b>DPPA2</b>, whereas the seven-membered ring of azulene is incorporated into the backbone of <b>DPPA3</b>. The LUMO energy of <b>DPPA3</b>, which was determined on the basis of the respective cyclic voltammograms and absorption spectra, is lower than those of <b>DPPA1</b> and <b>DPPA2</b>. OFETs were successfully fabricated with thin films of <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b>. Thin films of <b>DPPA1</b> and <b>DPPA2</b> exhibit p-type semiconducting properties with hole mobilities up to 0.97 cm² V^–1 s^–1, whereas typical ambipolar behavior is found for thin film of <b>DPPA3</b> with hole and electron mobilities reaching 0.062 cm² V^–1 s^–1 and 0.021 cm² V^–1 s^–1, respectively. The results reveal that semiconducting properties of <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> can be tuned by varying the linkage positions of azulene with DPP moieties. Furthermore, <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> were tested preliminarily as photovoltaic materials. The power conversion efficiency (PCE) reaches 2.04% for the blending thin film <b>DPPA1</b> with PC₇₁BM

Stereoelectronic Effect-Induced Conductance Switching in Aromatic Chain Single-Molecule Junctions

Biphenyl, as the elementary unit of organic functional materials, has been widely used in electronic and optoelectronic devices. However, over decades little has been fundamentally understood regarding how the intramolecular conformation of biphenyl dynamically affects its transport properties at the single-molecule level. Here, we establish the stereoelectronic effect of biphenyl on its electrical conductance based on the platform of graphene-molecule single-molecule junctions, where a specifically designed hexaphenyl aromatic chain molecule is covalently sandwiched between nanogapped graphene point contacts to create stable single-molecule junctions. Both theoretical and temperature-dependent experimental results consistently demonstrate that phenyl twisting in the aromatic chain molecule produces different microstates with different degrees of conjugation, thus leading to stochastic switching between high- and low-conductance states. These investigations offer new molecular design insights into building functional single-molecule electrical devices