Photoisomerization of azobenzene has been attracting a lot of researchers due to its excellent photoreactivity and various synthetic methods that enable various molecular design toward wide range of applications. Various type of photoswitching molecules have been proposed and intriguing phenomena have been reported in azobenzene-containing materials. This review commences with a brief description of recent progress of azobenzene-based materials that exhibit phenomena that can be visualized by eye (excluding color change) caused by photoisomerization. Successful examples such as bending crystals and polymer films, motion of objects, orientation of molecules, phase transitions, and aggregation-induced emission are described.

This review article summarizes the recent research on various stimuli-responsive circularly polarized luminescence (CPL) properties of π-electronic systems and related materials. Assembled structures of chiral π-conjugated polymers and molecules with emission properties showed tunable CPL resulting from the enhancement of chirality induction by aggregation in solutions and in the bulk states. As fascinating CPL-active species, pyrrole-based anion-responsive π-electronic systems, which have been prepared by the author, were found to exhibit CPL induced by anion binding, ion pairing, and formation of stacking structures.

By transient photoconductance under an external magnetic field (Magnetophotoconductance, MPC), we have investigated photocarrier dynamics in hexabenzocoronene (HBC) self-assemblies and [6, 6]-phenyl C₆₁ butyric acid methyl ester (PCBM) films. It was clarified that the lamination of electron acceptor layer on the surfaces of HBC nanotubular self-assemblies not only enhances the dissociation of exciton but also significantly reduces the recombination of geminate electron-hole pair in photocarrier generation. The time profiles of the MPC on e-h pair dynamics clarified the recombination ratio of the singlet and triplet e-h pairs with k_r^S : k_r^T = 1.0:0.8. The PCBM film also showed the MPC effect due to the recombination. In addition, a broad negative MPC effect, which was ascribed to the detrapping of carriers captured at trap site by collision with the triplet exciton, was detected by annealing the PCBM film at high temperatures.

We report directional far-infrared (> 30 µm) emission from the v = 0 level of the ns, np and nf (principal quantum number n > 9) Rydberg states of NO in the gas phase. The dominant emission process for the nf(v = 0) states is assigned as the nf → (n - 1)g transitions. The major emission process for the ns(v = 0) states is ascribed as the ns → (n - 1)p transition. In addition to these downward transitions, the excitation from ns to (n - 1)f located energetically above the ns states is identified. The possibility of optical transitions induced by black body radiation is briefly discussed.

Photomechanical effects observed for photochromic materials have been attracted a great deal of attention from both viewpoints of fundamental sciences and practical applications. In due course of our studies of the creation of low molecular-mass photochromic materials that readily form amorphous glasses, namely photochromic amorphous molecular materials, we have investigated photomechanical effects regarding photoinduced mass transport using azobenzene-based photochromic amorphous molecular materials. Our recent results are described here including photoinduced surface relief grating formation of amorphous films, photomechanical bending motions of molecular fibers, photoinduced mass flow at surface level of films, and photoinduced movements of fragments of amorphous glasses.

A combination of biomolecular motor protein systems and artificial photoresponsive molecules is useful for the building of light-driven molecular machines. Kinesin is a motor protein, which converts adenosine triphosphate (ATP) hydrolysis energy into mechanical work and unidirectionally moves along the microtubule rail protein. It must be beneficial to regulate artificially and utilize such a mechanical function of kinesin in in-vitro system as nano-devices. In fact, several researchers have tried to demonstrate the artificial regulation of kinesin motility with external stimuli so far, but almost all of them showed just one-time switching (i.e. irreversible response). We herein review our recent trials toward the photo-chemical and reversible control of the kinesin motility with a complete ON/OFF switching manner based on the photoisomerization of azobenzenes.