Electronic tuning effects via cyano substitution of a fused tetrathiafulvalene–benzothiadiazole dyad for ambipolar transport properties

Tuning Crystal Ordering, Electronic Structure, and Morphology in Organic Semiconductors: Tetrathiafulvalenes as a Model Case

“…The OFET mobility measured in nitrogen atmosphere was around 10 −2 cm 2 V −1 s −1 for holes and 10 −4 cm 2 V −1 s −1 for electrons, but in air the devices only showed p‐channel transport. Similar results showing ambipolar transport were obtained for the dyad formed by a 4,8‐dicyano substituted benzothiazole fused to a TTF (CN‐BTD‐TTF): μ h ≈ μ e ≈ 10 −5 cm 2 V −1 s −1 ) . Further, largely extended π‐conjugated electron deficient moieties that have been proved to behave as efficient n‐channel semiconductors such as perylenediimide (PDI) and naphtalenediimide (NDI), have also been fused to TTFs (Figure b) .…”

Tunable Lifetimes of Intramolecular Charge-Separated States in Molecular Donor–Acceptor Dyads

“…Figure shows OA spectra of the investigated samples in toluene, acetone, and DMF, ordered according to increasing permanent electric dipole and dielectric constant (Table and ref ). All samples show a clear band in the visible range that undergoes a blue shift moving through the series R = CN, Br, and H. With an extinction coefficient of around 10 –4 M –1 cm –1 and an oscillator strength of around 0.1, this band has been assigned to an optically allowed transition to the lowest singlet excited state showing an intramolecular charge-transfer character from the TTF to the BTD moiety. − , …”

“…Tetrathiafulvalene (TTF) − as an electron donor and benzothiadiazole (BTD) ,, as an electron acceptor are frequently incorporated into D–A systems for various applications in (opto)­electronic devices. They can be covalently fused to form single planar π-conjugated molecules, leading to an energetically low-lying intramolecular charge-transfer (ICT) transition from the highest-occupied molecular orbital (HOMO) localized on the donor fragment to the lowest-unoccupied molecular orbital (LUMO) on the acceptor part. − The resultant HOMO–LUMO band gap can be fine-tuned by the substitution at the 4- and 8-positions of the BTD unit (Chart ). A large red shift of the ICT absorption band has been attributed to a significant lowering of the energy of the LUMO levels due to the strong electron-withdrawing effect of Br and CN substituents compared to that of the unsubstituted TTF-BTD­(H) 2 .…”

“…A large red shift of the ICT absorption band has been attributed to a significant lowering of the energy of the LUMO levels due to the strong electron-withdrawing effect of Br and CN substituents compared to that of the unsubstituted TTF-BTD­(H) 2 . Consequently, TTF-BTD­(Br) 2 behaves as a p-type semiconductor whereas TTF-BTD­(CN) 2 behaves as an ambipolar semiconductor . This great tunability in so many physical properties, when compared with other π-conjugated systems and coordination complexes, motivates the application of such fused D–A systems in the field of molecular electronics or nonlinear optics. ,,− The study of their electronic tunability and charge-transfer characteristics is thus extremely valuable, and we recently carried out a study with Stark spectroscopy to elucidate the intimate link between the structural parameters and electronic features of the ground and excited states, such as polarizability and permanent dipoles .…”

Gold-linked strings of donor–acceptor dyads: on-surface formation and mutual orientation

“…4 Different approaches have been explored to provide specificity and directionality in molecular self-assembly via weak non-covalent interactions such as hydrogen bonding, 12,13 electrostatic interactions, [14][15][16][17] and metal-ligand coordination. [18][19][20][21] We synthesize a precursor by annulation of an electron donor and an electron acceptor, 3,22,23 leading to an intrinsic dipole moment of B5 Debye 23 along the molecular axis that is expected to steer the relative alignment of adjacent monomers. The low-energy configuration of dipoles would suggest an antiparallel head-to-tail ordering of monomers.…”