Optical Humidity Sensing Using Transparent Hybrid Film Composed of Cationic Magnesium Porphyrin and Clay Mineral

Fluorescence enhancement of benzimidazolium derivative on clay nanosheets by surface-fixation induced emission (S-FIE)

The photophysical behaviors of benzimidazolium derivative [4-(1,3-dimethylbenzimidazol-3-imu-2-yl)-N, N-diphenylaniline (2-(4-(diphenylamino)phenyl)-1,3-dimethyl-1H-benzo[d]imidazol-3-ium)] (BID) in water, organic solvents and on synthetic saponite were investigated. The fluorescence quantum yield (Φf) of BID was 0.91 on the saponite surface under the optimal condition, while that in water was 0.010. Such fluorescence enhancement on the inorganic surface is called "surface-fixation induced emission (S-FIE)". This fluorescence enhancement ratio for BID is significantly high compared to that of conventional S-FIE active dyes. From the values of Φf and the excited lifetime, the non-radiative deactivation rate constant (knr) and radiative deactivation rate constant (kf) of BID on the saponite surface and in water were determined. Results showed that the factors for fluorescence enhancement were both the increase of kf and the decrease of knr on the saponite surface; especially, knr decreased by more than two orders due to the effect of nanosheets.

Structural Transformation of Azonia[5]helicene Photoproduct via Reaction Field Function of Layered Inorganic Material

In an attempt to generalize "on surface synthesis", which has unique potential in the area of organic synthesis, the focus was placed on layered silicates having a highly flat surface. The photoreaction of (±)-13-bromo-6a-azonia[5]helicene (AHHBr) and (±)-2-bromo-13-methyl-6a-azonia[5]helicene (AHBrMe) in solution and within the layers was examined. In the case of AHBrMe, the photoproduct was different from that in solution. 1H nuclear magnetic resonance (NMR), Fourier transform-infrared spectroscopy (FT-IR), and electrospray ionization-mass spectrometry (ESI-MS) measurements revealed that the photoproduct obtained within the layers was a benzo-perylene molecule with a completely flat lactone structure (AL). This study is the first example of the successful conversion of a chemical reaction path due to the steric effect of the flat surface of layered silicate.

Vapor-Induced Assembly of a Platinum(II) Complex Loaded on Layered Double Hydroxide Nanoparticles

Controlled self-assembly of PtII complexes is key to the development of optical and stimuli-responsive materials, but designing and precisely controlling them is still difficult owing to weak intermolecular interactions. Herein, we report the successful water-vapor-induced assembly of an anionic PtII complex [Pt(CN)2 (ppy)]- (Hppy=2-phenylpyridine) electrostatically loaded onto cationically charged layered double hydroxide (LDH) nanoparticles consisting of Mg2+ and Al3+ ions. When the PtII complexes were densely loaded onto the LDH nanoparticles, the assembly was maintained, even in dilute aqueous media. In the case of sparse loading, the PtII complexes were loaded discretely in the dry state; however, when water vapor was adsorbed, the increased mobility of the PtII complexes led to their assembly on the LDH nanoparticles. The presence of water vapor led to a drastic change in luminescence from green to orange.

One-step solvent-free synthesis of carbon dot-based layered composites exhibiting color-tunable photoluminescence

We here report a practical and green approach to the development of luminescent composites through in situ solvent-free formation of carbon dots on layered inorganic compounds. The composites exhibit higher solid-state photoluminescence than those prepared by mixing of synthesized carbon dots and layered clay minerals. Tuning of the emission color of the composites has also been achieved by the addition of small molecules into phloroglucinol as starting materials for carbonization. The carbon dots synthesized in clay compounds in the solvent-free conditions are well-dispersed to obtain homogeneous composites. Furthermore, we have demonstrated that highly luminescent carbon dots are formed by carbonization in the presence of layered inorganic compounds. The one-step solvent-free approach presented in this work may allow not only facile, economical, and sustainable production of nanostructured carbon dot-based composites but also improvement of their luminescence properties.

A practical and green approach to the development of color-tunable luminescent composites through in situ solvent-free synthesis of carbon dots on layered inorganic compounds is reported.

Adsorchromism: Molecular Nanoarchitectonics at 2D Nanosheets-Old Chemistry for Advanced Chromism

Chromism induced by changes in the electronic states of dye molecules due to surface adsorption is termed "adsorchromism" in this article. These changes of molecular electronic states are induced by protonation, aggregation, intramolecular structural changes, and other processes, depending on the surface environment. Intramolecular structural changes, such as co-planarization and decreased molecular motion are the most characteristic and interesting behavior of dye molecules at the surfaces, resulting in spectral shift and/or emission enhancement. In this review, adsorchromism at the surfaces of layered materials are summarized since their flexibility of interlayer distance, surface flatness, and transparency is suitable for a detailed observation. By understanding the relationship between adsorchromism and the electronic states of molecules on the surfaces, it will be possible to induce some desired functions which can be realized simply by adsorption, instead of complicated organic syntheses. Thus, adsorchromism has potential applications such as effective solar energy harvesting systems, or biological/chemical sensors to visualize environmental changes.

Photoluminescence Gas Sensing by Fluorescein-Dye Anions/1-Butanesulfonate/Layered Double Hydroxide Hybrid Materials under Humid Environment Conditions

In this study, we investigated the photoluminous spectroscopic behavior of hybrid powder incorporating both anionic fluorescein dye (AFD) and 1-butanesulfonate (C4S) with layered double hydroxide (LDH) in the presence of NH₃ or NO₂ gas under various relative humidity conditions. In the presence of NH₃ gas, drastic photoluminescence enhancement from the LDH/AFD/C4S hybrid was observed at relative humidity (RH) ≥ 40% when the NH₃ reached a certain concentration. Meanwhile, the LDH/AFD/C4S hybrid was exposed to NO₂ gas at various relative humidity conditions, and the following behavior was observed: At RH ≥ 60%, the photoluminescence (PL) intensity from the hybrid gradually decreased as NO₂ concentration increased. Therefore, the LDH/AFD/C4S hybrid investigated in this study is inferred to be suitable for optical NH₃/NO₂ sensor devices, which can be used in humid air.