Polyacenes, composed of multiple linearly fused benzene rings, are an important class of polycyclic aromatic hydrocarbons. The unique electronic property stems from its zigzag-edged polyacene structure. The synthetic development of polyacene and evaluation of their electronic properties significantly contribute not only to proper molecular design of organic semiconducting materials but also to our understanding of the edge states of zigzag-type graphene nanoribbons. The first part is general introduction of polyacenes, showing pentacene as a benchmark compound for organic semiconducting materials. The second part outlines how to synthesize polyacene using “precursor method”. The third part focuses on the on-surface synthesis of polyacenes. Specifically, the bandgap and biradical character of polyacene are provided and discussed. The fourth part outlines the polyacene synthesis under anaerobic conditions such as an interior of a single crystal and a metal-organic framework. The final section presents a conclusion and perspective.

Cerium is the most abundant element among lanthanides in the earth's upper crust, and actually a waste product from the supply chain of rare earth elements. Development of value-added materials from earth-abundant cerium is therefore of long-standing interest for the purposes of sustainable chemistry. Recently, a range of progress regarding bright emission and photocatalytic reactions of cerium complexes has been made and this will be the main focus of this review. 4f–5d transition of Ce (III) ion is parity allowed in contrast with the forbidden f–f transition of other lanthanide ions. Recent advances in 4f–5d emitting Ce (III) complexes including our study of [Ce^III(SCN)_n] are reviewed. Both the +3 and +4 oxidation states of cerium are easily accessible. Photocatalytic C–C bond forming and C–H bond functionalization reactions exploiting the Ce (III) / Ce (IV) redox couple are also described.

This review summarizes molecular photofunctions based on molecular magnetism, i.e., spin angular momenta and orbital angular momenta. From the viewpoint of spin manipulations of photoexcited states, the development of fluorescent probes for detecting vitamin C is illustrated. Also, the proposal of molecular magneto-optical memory and the magneto-chiral dichroism of organic compounds are introduced, which have been achieved by the use of orbital angular momenta of aromatic conjugated systems. Thus, this review demonstrates that the photofunctions based on molecular magnetism can open up novel scientific fields and technologies.

Circularly polarized luminescence (CPL) is a phenomenon in which a chiral molecule emits light with a difference in intensity between right and left circularly polarized light. CPL allows the development of not only smarter photonic materials for advanced technologies, such as 3D displays but also provide bioimaging, hence CPL in the near-infrared (NIR) region is also an interesting research field. Highly efficient CPL requires strong luminescence properties and excellent anisotropy. However, CPL in the NIR region has been much less studied than in the visible light region, because luminescence in the NIR region is not strong due to thermal deactivation. The author and coworkers observed CPL in the visible light region by modifying the fluorescence properties of highly anisotropic helicenes. Furthermore, they synthesized dipyrromethene complexes that exhibit strong fluorescence in the NIR region. Based on these studies, they investigated molecular systems for CPL in the NIR region. The results are presented in this paper.

For the development of thermally activated delayed fluorescence (TADF) materials, the kinetic analysis is crucial to estimate the rate constants of each photophysical process. Until now, however, a wide variety of rate equations has been formulated with different assumptions. Since most of the rate equations are assuming non-radiative decay from singlet or triplet as zero, they cannot apply to low emissive materials. Also, the conventional estimation method for prompt and delayed emission efficiency should be corrected. In this report, we formulated the accurate kinetic rate equations to analyze the three-state photophysics. Further, we provided the accurate analysis method to evaluate the effective spin-orbit coupling strength from the temperature dependence of the rate constants. We believe that these advanced photophysical parameters provide the design rule for high performance TADF materials.

There is an intensive demand to develop technologies utilizing carbon dioxide (CO₂) as a carbon resource to realize a sustainable society. However, the thermodynamic stability of CO₂ stands as a formidable hurdle to the development. Although synthetic chemists have tried to develop reactions incorporating CO₂ into organic molecules, the success remains significantly limited. Here we describe our findings on photoinduced carboxylation of C–H bonds with CO₂. The discovery includes the development of new reactions incorporating CO₂ into (i) a benzylic C–H bond of o-alkylphenyl ketones, (ii) an allylic C–H bond of simple alkenes, and (iii) an aliphatic C–H bond of alkanes.