About Dendrimers: Structure, Physical Properties, and Applications

Perylene bisimide dyes as versatile building blocks for functional supramolecular architectures

Over the 100 years since its discovery, liquid crystals have been the intriguing subject for both academia and industries. The textbook of de Gennes The Physics of Liquid Crystals published in 1974 is still the bible for many LC researchers, but new subjects unmentioned in the book have also risen for these years. This chapter describes the story of the recent developments and the future perspectives in physics of liquid crystals, especially focusing on the contributions by Japanese research groups for the last decade.

Physics of Liquid Crystals

J-aggregates are of significant interest for organic materials conceived by supramolecular approaches. Their discovery in the 1930s represents one of the most important milestones in dye chemistry as well as the germination of supramolecular chemistry. The intriguing optical properties of J-aggregates (in particular, very narrow red-shifted absorption bands with respect to those of the monomer and their ability to delocalize and migrate excitons) as well as their prospect for applications have motivated scientists to become involved in this field, and numerous contributions have been published. This Review provides an overview on the J-aggregates of a broad variety of dyes (including cyanines, porphyrins, phthalocyanines, and perylene bisimides) created by using supramolecular construction principles, and discusses their optical and photophysical properties as well as their potential applications. Thus, this Review is intended to be of interest to the supramolecular, photochemistry, and materials science communities.

J-aggregates: from serendipitous discovery to supramolecular engineering of functional dye materials.

In the 21st century, soft materials will become more important as functional materials because of their dynamic nature. Although soft materials are not as highly durable as hard materials, such as metals, ceramics, and engineering plastics, they can respond well to stimuli and the environment. The introduction of order into soft materials induces new dynamic functions. Liquid crystals are ordered soft materials consisting of self-organized molecules and can potentially be used as new functional materials for electron, ion, or molecular transporting, sensory, catalytic, optical, and bio-active materials. For this functionalization, unconventional materials design is required. Herein, we describe new approaches to the functionalization of liquid crystals and show how the design of liquid crystals formed by supramolecular assembly and nano-segregation leads to the formation of a variety of new self-organized functional materials.

Functional liquid-crystalline assemblies: self-organized soft materials.

Banana-Shaped Compounds—A New Field of Liquid Crystals

A series of perylene tetracarboxylic acid bisimides 3 a–e bearing 3,4,5-tridodecyloxyphenyl substituents on the imide N atoms and zero, two, or four phenoxy-type substituents in the bay positions of the perylene core were synthesized. From investigations of their spectroscopic properties and aggregation behavior in low-polarity solvents by absorption and fluorescence optical spectroscopy, not only were these compounds found to form fluorescent J-type aggregates, but also binding constants for aggregation could be derived which reflect the number and steric demand of the phenoxy substituents for bisimides 3 a–d. In the pristine state, 3 a–d form thermotropic hexagonal columnar mesophases which exist over a broad temperature range from below −30 °C to over 300 °C. For the tetraphenoxy-substituted compound 3 e, however, a layered crystalline structure was found. This difference in behavior can be explained by the concept of microphase segregation of the aromatic cores of the molecules and the alkyl chains at the periphery. The high stability and bright fluorescence of the mesophase of several of the compounds make them promising for applications as polarizers or components in (opto)electronic devices.

Fluorescent J‐type Aggregates and Thermotropic Columnar Mesophases of Perylene Bisimide Dyes

In this paper we present selected members of 7 new series of bent-shaped five-ring resorcinol derivatives which are distinguished by substituents at the central core as well as at the outer rings. Depending on the kind and position of the substituents and depending on the length of the terminal chains not only have new mesophases (the CPA phase or three unidentified B2-like phases) been identified, but also interesting phase sequences have been observed (B2–N; B2–SmA; B2–SmA–SmC; B2–SmA–SmC–N).

Influence of lateral substituents on the mesophase behaviour of banana-shaped mesogens

Novel bent-core (banana-shaped) liquid crystals without Schiff-base units have been synthesized and investigated by polarized light optical microscopy, differential scanning calorimetry, X-ray scattering, and electrooptical investigations. These molecules are 4-(4-alkylbenzoyloxy)benzoates and 4-(4-alkoxybenzoyloxy)benzoates of resorcinol, 3,4‘-dihydroxybiphenyl, and 4,4‘ ‘-dihydroxy-1,1‘:3‘,1‘ ‘-terphenyl. Three different mesophases were found depending on the molecular structure and the length of the terminal alkyl chains:  a rectangular columnar phase, a highly ordered low-temperature mesophase, and an antiferroelectric switchable fluid smectic mesophase designated as SmCPA. The influence of the molecular structure on the occurrence of the SmCPA phase was investigated. The spontaneous polarization of these molecules is quite high (PS = 500−700 nC cm-2) and specially those molecules with long alkyl chains and short bent-core structures have low melting points and broad regions of this switchable mesopha...

Molecular Design of Nonchiral Bent-Core Liquid Crystals with Antiferroelectric Properties

Chirality and Macroscopic Polar Order in a Ferroelectric Smectic Liquid-Crystalline Phase Formed by Achiral Polyphilic Bent-Core Molecules This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.

Siegmar Diele

Papers

Banana-Shaped Compounds—A New Field of Liquid Crystals

Fluorescent J‐type Aggregates and Thermotropic Columnar Mesophases of Perylene Bisimide Dyes

Influence of lateral substituents on the mesophase behaviour of banana-shaped mesogens

Molecular Design of Nonchiral Bent-Core Liquid Crystals with Antiferroelectric Properties

Chirality and Macroscopic Polar Order in a Ferroelectric Smectic Liquid-Crystalline Phase Formed by Achiral Polyphilic Bent-Core Molecules This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.