ma502306f_si_001.pdf (2.13 MB)
Naphthodithiophene Diimide (NDTI)-Based Semiconducting Copolymers: From Ambipolar to Unipolar n‑Type Polymers
journal contribution
posted on 2015-02-10, 00:00 authored by Masahiro Nakano, Itaru Osaka, Kazuo TakimiyaA series of naphthodithiophene diimid
(NDTI) based semiconducting
polymers with various comonomer units, i.e., thienylenevinylene (TV),
naphtho[1,2-b:5,6-b′]dithiophene
(NDT), vinylene (V), benzo[c][1,2,5]thiadiazole (BTz),
and naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole
(NTz), were synthesized by Stille coupling or copper iodide-assisted
Stille coupling using 2,7-dibromo-NDTI or 2,7-bis(trimethylstannyl)-NDTI,
respectively. Their HOMO and LUMO energy levels were estimated by
cyclic volttammetry and photoelectron spectroscopy. The HOMO energy
levels of the NDTI-based polymers were strongly affected by the electronic
nature of the comonomer units. In contrast, their LUMO energy levels
were almost identical, likely owing to their localized LUMOs on the
NDTI moiety. All the polymers showed air-stable electron transport
in the field-effect transistors (FETs), thanks to their low-lying
LUMO (∼−4.0 eV), as ambipolar (PNDTI-TV, -NDT, ∼0.082
cm2 V–1 s–1, μe = ∼0.029 cm2 V–1 s–1) or unipolar n-channel materials (PNDTI-V,
-BTz, PNDTI-NTz, μe = ∼0.21 cm2 V–1 s–1), depending on their HOMO energy levels. These
results indicate that the type of active carrier in the NDTI-based
polymers can be controlled by the nature of comonomer units. Moreover,
the two-dimensional grazing incidence X-ray diffraction (2D GIXD)
indicated that the polymers with linear backbone structures and large
space between the branched alkyl chains tend to afford well-organized
crystalline thin film with the edge-on orientation, consistent with
good transport characteristics in their FET devices.