Scattering is one of the most important techniques for the research of structural chemistry. Scattering is classified into three categories; elastic, inelastic, and quasi-elastic. Quesi-elastic scattering is a technique to measure the fluctuation of the target as the energy broadening of scattered waves. Quesi-elastic light scattering, which is called dynamic light scattering, is used for the estimation of the diffusion constant of the polymer and colloidal particles in solution. A drawback of dynamic light scattering is the lack of molecular selectivity since the scattered light used for dynamic light scattering is Rayleigh scattering. This account describes how to achieve molecular-selective dynamic light scattering. The basic idea is the use of inelastic (Raman) scattering instead of elastic (Rayleigh) scattering. It is derived that the fluctuation of the scattered light intensity is not observed from Raman scattering and phase-matching coherent Anti-Stokes Raman scattering (CARS) but from phase-mismatching CARS, which is named as dynamic Raman scattering. A proof-of-principle experiment of dynamic Raman scattering is also introduced.

Ligand-protected metal nanoclusters are easily obtained by simply mixing reagents in a solution and have relatively high stability due to their protection by organic ligands. Furthermore, their geometrical structures can be revealed by single-crystal X-ray diffraction analysis. Recently, it has been reported that the size-specific electronic/geometric structures of these metal nanoclusters can be utilized in many applications as highly active and selective catalysts. In this study, we deepened our understanding of the interaction between the metal core and the organic ligands protecting the metal nanoclusters, as well as the desorption behavior of the ligands under calcination conditions, which is important for the use of the metal nanoclusters as heterogeneous catalysts. Furthermore, based on this understanding, we showed that metal nanocluster-loaded catalysts with appropriate pretreatment exhibit higher activity as electrochemical/photoelectrochemical catalysts compared to conventional catalysts. These findings are expected to make a significant contribution toward further catalytic applications using metal nanoclusters with more diverse metal species, number of constituent atoms, and geometric structures, as well as their assemblies.

Accurate quantum chemical methods are reliable due to their rigorous treatment of the wavefunction. However, it is known that optimizing molecular geometries using these methods is not straightforward, owing to the lack of analytic derivatives of the computed energy. This account briefly describes the analytic derivative theory of variational and non-variational methods as well as the multiconfiguration and multireference methods. For non-variational methods, we utilize the Z-vector or Lagrangian methods to avoid explicitly computing derivatives of wavefunction parameters. The developed method is applied to determining minimum energy structures on adiabatic potential energy surfaces and crossings between them (conical intersections). The selected examples demonstrate that the developed methods are useful for accurately describing (photo)chemical properties.

Electronic excited states play a central role in photo-energy and photo-material conversion processes such as photosynthesis, photovoltaics and photocatalysis. Although molecules inherently possess diverse excited states at a higher energy level, such excited states are rapidly deactivated into the lowest excited state via ultrafast internal conversion. Thus, electronic excited states we can utilize for creation of novel photoresponses and photofunctions are limited to be the lowest excited state in a given spin multiplicity, as advocated as Kasha's rule. However, recent studies have reported exceptional reaction behavior in higher excited states not only for classical examples such as porphyrin and azulene but also for emergent molecular systems playing a key role in materials science and biology. In this context, excited states lying at the higher energy level are one of frontier left in molecular science. In this article, we introduce recent advances in our studies on photochemical reactions such as isomerization, ionization, and electron transfer in the higher excited state revealed by multiple excitation spectroscopy. In addition, we describe exciton diffusion dynamics in molecular aggregates which involve more diverse electronic states and show more elaborate photophysical properties and functions than single-molecule level.

Ion mobility-mass spectrometry (IM-MS), which combines ion mobility spectrometry with mass spectrometry, has become one of the standard analytical methods by obtaining structural information as collision cross sections. This method was applied to gas-phase atomic cluster ions and supramolecular ions in addition to simple organic molecules by the authors for the past two decades. After noting the principles of this method, details were shown for the experimental apparatuses and analytical processes. As a result of the studies, three topics were presented: (1) Structures and adsorption reactions of transition metal oxide cluster cations, (2) structures and isomerization reaction of the complexes between crown ethers with guest ions, and (3) intramolecular proton transfer reactions of organic molecules induced by a collision with a single molecule.

I introduce the Red Moon (RM) approach based on an efficient and systematic new RM method for dealing with complex reaction (CR) systems that exhibit chemical phenomena typical of molecular aggregation states. First, the theoretical background of the RM approach is presented, which was developed due to the need to perform "atomistic" molecular simulations of large-scale and long-term phenomena such as (i) complex chemical reactions, (ii) stereospecificity, and (iii) aggregation structures. I also mention its critical characteristics, touching on the assumption of landscape similarity. The RM approach uses molecular dynamics (MD) for molecular motions (translation, rotation, and vibration) that frequently occur on short time scales, and Monte Carlo (MC) for rare events, such as chemical reactions that rarely occur on that time scale. The MC method is then used to test and determine if the trial is feasible under the transition rate, which is evaluated by the potential energy difference before and after the trial of the rare event and its chemical kinetic probability (Metropolis method). Next, typical applications of the RM method in two main research areas, (i) polymerization and (ii) storage batteries (rechargeable and secondary batteries), will be reviewed along with various examples of our successful studies. Finally, I conclude that the RM approach using the RM methodology should be an efficient new-generation approach as one of the promising computational molecular technologies (CMT). I believe that the RM approach will play an essential role in investigating various specificities of CR systems in molecular aggregation states at multi-level resolution.