Control of Molecular Structure in the Generation of Highly Luminescent Liquid Crystalline Perylenebisimide Derivatives:  Synthesis, Liquid Crystalline and Photophysical Properties

Abstract

We report here, for the first time, the role of the molecular design on the liquid crystalline and solid-state photoluminescent properties of soluble and thermally stable liquid crystalline perylenebisimide derivatives. A new series of perylenebisimides were designed and developed for this purpose by adopting the stoichiometry-control approach, and amine-, hydroxyl-, ester-, and amide-functionalized molecules were synthesized. Various types of spacers with different lengths (C(2) to C(12)), types (linear, cyclohexyl, and tricyclodecane), and end-capped by phenyl or tridodecyloxy gallic units were introduced in the perylenebisimide core. The molecules were completely characterized by NMR, FT-IR, SEC, and MALDI-TOF mass techniques. Thermal analysis revealed that the perylenebisimide derivatives were thermotropic liquid crystalline, and threadlike nematic phases were observed under a polarizing light microscope. The spacer length and the rigidity of the spacers play a major role in the liquid crystalline properties of the materials. In phenyl systems, the C(6) chain with ester- and the C(12) chain with amide-end-capped molecules showed a nematic phase, whereas the C(6) chain with an amide end cap and their cyclic and tricyclic counterparts did not show any LC property. The introduction of a tridodecyloxy gallic unit induced the LC property in C(12) and the cyclohexyl system; however, it failed to do so in the tricyclodecane molecule. The absorption properties of the molecules were almost unchanged by the structural variation; however, the emission quantum yield in solution and photoluminescent (PL) intensity in the solid state were significantly different. Though the gallic unit induced liquid crystallinity in the perylenebisimide core, the quantum yield and PL intensity are 4-5 times less compared to those of the simple phenyl-capped liquid crystalline system. Among the various types of spacers, the tricyclodecane induced strong molecular aggregates via pi-stacking, which in turn increased the rigidity of the entire perylenebisimide core, resulting in the absence of liquid crystallinity and low luminescence compared to their linear and cyclohexyl analogues. The molecular aggregates were very stable even at very dilute concentration and also at high temperatures. The aggregates disappeared immediately upon addition of trifluoroacetic acid, thus confirming the strong hydrogen bonding in the aggregated states. In a nutshell, the present report demonstrates the importance of molecular design for introducing liquid crystalline phases in perylenebisimides and also the development of novel highly luminescent n-type pi-conjugated material for application in optoelectronics.

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

“…This property is essential for solution processability, illustrating the need for n‐type polymers. Perylene bisimides (PBI) are a relevant class of n‐type semiconductors due to their relatively high electron affinity and strong visible‐light absorption, combined with good photochemical and thermal stability 9, 10. Due to strong π–π interaction of the perylene cores, electron mobilities of 0.1–1 cm 2 V −1 s −1 for low molecular weight PBIs and 1.2 × 10 −3 cm 2 V −1 s −1 for a solution processable PBI side‐chain homopolymer in organic field‐effect transistors were reported 11, 12.…”

Synthesis of Alternating Copolysiloxane with Terthiophene and Perylenediimide Derivative Pendants for Involatile WORM Memory Device

“…Additionally, the low HOMO energy of most PDI derivatives facilitate the hole transfer to the conjugated polymer after absorption of light by the PDI molecule and the excited state of the PDI can be transferred to the donor polymer depending on the driving force of the processes. Moreover, PDI derivatives also display excellent photochemical and thermal stability . Taking these distinctive natures of perylenebisimide into account, the incorporation of PDI into donor–acceptor polymers as an electron acceptor is confirmed to be effective stabilizing radical anion induced by charge transfer (CT) from donor to acceptor, resulting in nonvolatile memory characteristics with a stable CT state.…”

Novel Pentadecyl Phenol‐Tagged L‐Tryptophan Molecules: Synthesis, Self‐ Assembly and Liquid Crystalline Properties

“…Hence a balance between the rigid aromatic core and the flexible alkyl spacers are necessary for inducing liquid crystalline phases. The introduction of rigid amide linkages, flexible alkyl spacers, or aromatic core could affect this balance and hence the LC properties . In solvents such as tert‐butanol and benzyl alcohol, crystalline/LC behavior were observed, while methanol induces a spontaneous self‐assembly resulted in spherical morphology.…”