Luminescent Cu(I) complexes have recently attracted considerable attention because of their interesting photophysical properties including high emission quantum yield and tunable emission color. Moreover, due to the low cost and abundance of Cu resource, these complexes show great potential for industrial application as alternative materials to the luminescent noble metal Ru(II), Ir(III), and Pt(II) complexes. However, the stability of Cu(I) complexes, especially in solution, is generally lower than that of noble metal complexes. Thus, the development of alternative techniques to the traditional solution reactions is strongly required for the preparation of thin-film light emitting devices based on Cu(I) luminophores. In this paper, mechanochemical synthesis of luminescent Cu(I) complexes is reviewed, because this technique is recently found to be applicable for the preparation of various Cu(I) luminescent materials.

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Photoacid generators, PAGs, are one of the most important industrial chemicals in electronics processing. They are practically used in photopattern formation with positive and negative photoresists, photo-curable resins, and printing technologies. Photodynamic therapy and other photo-stimulation for biological systems are also involved in the application fields of PAGs. In this article, the authors present an overview of progress in the development and photochemistry of PAGs. PAGs are categorized into two classes, the ionic and the non-ionic PAGs, the former has been developed in advance to the latter class and easily generates strong acids. Expansion of wavelength of photo-activation in both classes of PAGs is briefly discussed. Self-contained type PAGs have also been proposed and expanded for super-acid generation with highest photochemical quantum yields seen among non-ionic PAGs.

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α,ω-Diphenylpolyenes have long received considerable attention due to their interesting photophysical/chemical properties and are expected to be potential optical and photofunctional materials. Among them, 1,6-diphenyl-1,3,5-hexatriene (DPH) is known to be the shortest chromophore whose lowest singlet state has A_g symmetry, and its spectroscopic properties have been intensively studied in solution. In contrast, the solid-state properties of DPH are still almost unknown. We have systematically investigated the crystal structures and fluorescence properties of unsubstituted and ring-substituted DPHs to clarify the strong relationship between molecular arrangements and emission properties. In this review, we describe our recent study on halogenated (F, Cl, Br or I) DPHs. The experimental data can be interpreted in terms of strong excitonic interaction in the crystals due to the large transition dipole moments along the long molecular axis, as shown by quantum chemical calculations.

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Large acenes composed of linearly fused more than five benzene rings are simple polycyclic aromatic hydrocarbons. However, it is normally difficult to synthesize large acenes because of the low solubility and stability. To overcome these problems, we have developed “photochemical precursor method”. Here, we report the on-surface formation of heptacene and nonacene via photochemical precursor method on Au(111) to provide experimental insight into the chemical and electronic structure of large acenes. In addition, we also report the on-surface formation of heptacene organometallic complexes on Au(111) under ultrahigh vacuum conditions. Scanning tunneling microscopy and non-contact atomic force microscopy revealed the formation of Au-heptacene complexes via a selective two-step activation of α-diketone-type precursors. Finally, we applied copolymerization approach of using suitable linkers as additional reactants to the formation of fully conjugated polycyclic nanowires containing heptacene moieties.

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Great studies have been made in the past decade toward the development of solid-state emissive materials that exhibit mechanochromic luminescence (MCL), i.e., mechanical-stimuli-induced reversible color change of the solid-state emission. However, the generation of organic crystals with specific MCL behavior remains a challenging task due to the lack of the design principle of MCL-active crystals. Herein, a systematic study of indolylbenzothiadiazoles as self-recovering MCL-active organic crystals with different emission colors and recovery times is described. In addition, a series of phenanthroimidazolylbenzothiadiazoles exhibit more versatile MCL properties. Bathochromically or hypsochromically shifted bicolor MCL as well as tricolor MCL are observed due to the formation of different crystal structures. We also propose a novel strategy to achieve tricolor MCL, which is based on crystals of mixed two organic dyes. The underlying design principle obtained in these studies should accelerate the development of a wide variety of new MCL materials.

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Semiconducting small molecules that can self-organize into well-defined nanostructures have a great potential in organic electronics. Among various nanostructures, one-dimensional nanorods are reasonable entities as media for the quasi-one-dimensional charge carrier transport in optoelectronic devices. In this article we review hydrogen-bond-directed supramolecular organization of barbiturated oligothiophenes and the application of the resulting one-dimensional nanostructures to solution processable bulk heterojunction organic photovoltaic cells. An appropriate molecular design enabled us to utilize directional hydrogen bonding units as potent tool to organize π-conjugated molecules into one-dimensional nanostructures that are optoelectronically active in the device level.

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