Periodicity of molecular clusters based on symmetry-adapted orbital model

The periodic table has always contributed to the discovery of a number of elements. Is there no such principle for larger-scale substances than atoms? Many stable substances such as clusters have been predicted based on the jellium model, which usually assumes that their structures are approximately spherical. The jellium model is effective to explain subglobular clusters such as icosahedral clusters. To broaden the scope of this model, we propose the symmetry-adapted orbital model, which explicitly takes into account the level splittings of the electronic orbitals due to lower structural symmetries. This refinement indicates the possibility of an abundance of stable clusters with various shapes that obey a certain periodicity. Many existing substances are also governed by the same rule. Consequently, all substances with the same symmetry can be unified into a periodic framework in analogy to the periodic table of elements, which will act as a useful compass to find missing substances

Photochemical Properties of Mono‑, Tri‑, and Penta-Cationic Antimony(V) Metalloporphyrin Derivatives on a Clay Layer Surface

Three types of mono-, tri-, and penta-cationic antimony­(V) porphyrin derivatives (Sb^VPors) were synthesized, and their photochemical properties on the anionic clay were systematically investigated. Sb^VPor derivatives are dihydroxo­(5,10,15,20-tetraphenylporphyrinato)­antimony­(V) chloride ([Sb^V(TPP)­(OH)₂]⁺Cl^–), dihydroxo­[5,10-diphenyl-15,20-di­(<i>N</i>-methyl-pyridinium-4-yl)­porphyrinato]­antimony­(V) trichloride ([Sb^V(DMPyP)­(OH)₂]³⁺3Cl^–), and dihydroxo­[5,10,15,20-tetrakis­(<i>N</i>-methyl-pyridinium-4-yl)­porphyrinato]­antimony­(V) pentachloride ([Sb^V(TMPyP)­(OH)₂]⁵⁺5Cl^–). The photochemical behaviors of three cationic Sb^VPors with and without clay were examined in aqueous solution. For all Sb^VPor, aggregation behaviors were not observed in the clay complexes even at high density adsorption conditions. The transition probabilities and fluorescence quantum yields of Sb^VPor showed a tendency to be increased by the complex formation with clay. The less cationic Sb^VPor/clay complex showed the larger fluorescence quantum yield. The more cationic Sb^VPor/clay complex showed the longer fluorescence lifetime. These effects of complex formation with clay on the photochemical properties of Sb^VPors were discussed using the molecular potential energy curves of the porphyrin ground state and excited state. It is concluded that two types of effects work in the Sb^VPor/clay system: effect i (structure resembling effect) is that the most stable structure becomes relatively similar between the ground and excited states, mainly by hydrophobic interactions between the porphyrin molecule and the clay surface, and effect ii (structure fixing effect) is that sharpened potential energy curves of clay complexes can lead to the increase of activation energy for the internal conversion from excited state to a high vibration level of ground state, mainly by electrostatic interactions between cationic porphyrin and anionic clay. Like this, the unique effects of the clay surface on the photochemical behavior of dyes were observed and the mechanisms were rationally discussed

Controlled Synthesis of Au25 Superatom Using a Dendrimer Template

Superatoms are promising materials for their potential in elemental substitution and as new building blocks. Thus far, various synthesis methods of thiol-protected Au clusters including an Au25 superatom have been investigated. However, previously reported methods were mainly depending on the thermodynamic stability of the aimed clusters. In this report, a synthesis method for thiol-protected Au clusters using a dendrimers template is proposed. In this method, the number of Au atoms was controlled by the stepwise complexation feature of a phenylazomethine dendrimer. Therefore, synthesis speed was increased compared with the case without the dendrimer template. Hybridization for the Au25 superatoms was also achieved using the complexation control of metals

Unique Photochemical Properties of <i>p</i>‑Substituted Cationic Triphenylbenzene Derivatives on a Clay Layer Surface

Two types of novel tricationic 1,3,5-triphenylbenzene (TPB) derivatives were synthesized. The TPB derivatives are 1,3,5-tris­(<i>N</i>,<i>N</i>,<i>N</i>-trimethylanilinium-4-yl)­benzene (TMAB) and 1,3,5-tris­[(<i>N</i>-pyridinium)­aniline-4-yl]­benzene (TPAB). The photochemical behaviors of both cationic TPBs with and without clay were examined in aqueous solution. For both TPBs, the aggregation behavior was not observed in the clay complexes even at saturated adsorption conditions. Interestingly, the fluorescence intensity of TPAB was extremely increased by the complex formation with clay compared to that without clay in a bulk aqueous solution, although the increase of fluorescence was not observed for TMAB. Time-resolved fluorescence measurement revealed that the increase of fluorescence turned out to be due to the suppression of the nonradiative deactivation process from its excited singlet state, because the molecular motion of TPAB should be restricted due to the strong fixation on the clay surface. TPAB exhibited a little self-fluorescence quenching behavior as the loadings increased, while TMAB exhibited obvious self-fluorescence quenching on the clay surface. The difference of adsorption strength of TPBs onto the clay surface is supposed to affect their photochemical properties such as the increase of fluorescence and the self-fluorescence quenching behavior in the excited singlet state. It was found that the pyridinium substituent as cationic sites is beneficial to construct efficient photochemical reaction systems using a clay complex without unexpected fluorescence quenching

Photophysical Properties and Adsorption Behaviors of Novel Tri-Cationic Boron(III) Subporphyrin on Anionic Clay Surface

Two types of +3-charged subporphyrin derivatives with <i>m</i>- and <i>p</i>-methylpyridinium as the <i>meso</i>-aryl substituents were designed and synthesized. Their photophysical properties with and without anionic saponite clay were investigated. These cationic subporphyrins were suitably designed for adsorption on the saponite nanosheet surface with their photoactivity. Absorption and emission spectra of these subporphyrin-saponite complexes exhibited strong bathochromic shifts due to the flattening of the molecules on the nanosheet. This behavior was observed as drastic visual changes in their luminescence colors. Additionally, aggregation behaviors were not observed in the saponite complexes even at high dye loading levels for both subporphyrins. Moreover, under such condition, their fluorescence properties on the saponite surface were not only maintained but also enhanced without unexpected deactivations despite the dye molecules are densely introduced on the solid surface. These findings are beneficial for applications of the dye–clay complexes to photofunctional materials such as strongly luminescent materials, highly sensitive clay sensors and artificial photosynthesis systems