Liquid‐Crystalline Perylene Diester Polymers with Tunable Charge‐Carrier Mobility

Abstract

New classes of liquid‐crystalline semiconductor polymers based on perylene diester benzimidazole and perylene diester imide mesogens are reported. Two highly soluble side‐chain polymers, poly(perylene diester benzimidazole acrylate) (PPDB) and poly(perylene diester imide acrylate) (PPDI) are synthesized by nitroxide‐mediated radical polymerization (NMRP). PPDB shows n‐type semiconductor performance with electron mobilities of 3.2 × 10−4 cm2 V−1 s−1 obtained in a diode configuration by fitting the space‐charge‐limited currents (SCLC) according to the Mott–Gurney equation. Interestingly, PPDI performs preferentially as a p‐type material with a hole mobility of 1.5 × 10−4 cm2 V−1 s−1, which is attributed to the less electron‐deficient perylene core of PPDI compared to PPDB. Optical properties are investigated by UV‐vis and fluorescence spectroscopy. The extended π‐conjugation system due to the benzimidazole unit of PPDB leads to a considerably broader absorption in the visible region compared to PPDI. HOMO and LUMO levels of the polymers are also determined by cyclic voltammetry; the resulting energy band‐gaps are 1.86 eV for PPDB and 2.16 eV for PPDI. Thermal behavior and liquid crystallinity are studied by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction measurements. The results indicate liquid‐crystalline order of the polymers over a broad temperature range. These thermal, electrical, and optical properties make the perylene side‐chain polymers attractive materials for organic photovoltaics.

Pendant perylene polymers with high electron mobility

“…Moreover, the polymers show different degrees of aggregation. The direct NMRP of acrylate monomers carrying similar perylene chromophores was studied and reported earlier . In the direct synthesis, we could not achieve as high molecular weights as those obtained here with the click chemistry route.…”

“…This can help in optimizing morphology and hence device performance. When compared with directly synthesized acrylate polymers carrying similar chromophores, the polymers here presented show a slightly different thermotropic behavior. The directly polymerized PPDEB shows a T m at 312 °C, whereas the clicked counterpart exhibits T m at 285 °C.…”

“…In this context, perylene bisimides (PBIs) and related molecules such as perylene diester benzimidazole (PDEB) and perylene diester imide (PDEI) with their favorable absorption properties in the visible wavelength regime are a promising class of semiconductor dyes. Besides PBI, PDEI, and PDEB have already been incorporated in side‐chain polymers . PDEB shows an enhanced absorption up to 700 nm and PDEI absorption is blue‐shifted when compared with PBI.…”

Self-assembly, optical and electrical properties of five membered O- or S-heterocyclic annulated perylene diimides

“…The heteroatom actually help firming up the stacking of the molecules through non-covalent interactions, and electrostatic attraction between the electron-rich atom O/S and electronpoor perylene core. PDIs are among the most insoluble organic pigments and their processing into nanostructures by selfassembly protocols in solution has so far only been accomplished for derivatives bearing long n-alkyl side chains or basing on large pscaffold contortion [18]. This study will be helpful for exploring feasible routes to acquire well defined organic nanostructures.…”

Scandium‐catalyzed synthesis of Si–H‐containing syndiotactic polystyrene and its functionalized polymer carrying pendant perylene bisimide units

“…The broad reflection at 2 θ = 25.53° in the wide angle regime depicts a moderate intracolumnar long‐range order with a π–π stacking distance of 3.48 Å . These results indicate the organization and regular packing of PBI units in s PS‐PBI at liquid crystalline phase, which would be important to the potential application in devices such as field‐effect transistors, electroluminescent displays and photovoltaic cells as a charge‐transport materials …”