Cover: Dynamics of laser‐induced alignment and surface grating formation of azobenzene polymer were examined in relation to the photoisomerization pathway of the excited states. Further details can be found in the Full Paper by M. J. Kim*, J. D. Lee, C. Chun, D. Y. Kim, S. Higuchi, and T. Nakayama on page 1753.

The atomic-layered semiconducting materials of transition metal dichalcogenides are considered effective light sources with both potential applications in thin and flexible optoelectronics and novel functionalities. In spite of the great interest in optoelectronic properties of two-dimensional transition metal dichalcogenides, the excitonic properties still need to be addressed, specifically in terms of the interlayer interactions. Here, we report the distinct behavior of the A and B excitons in the presence of interlayer interactions of layered MoS2 crystals. Micro-photoluminescence spectroscopic studies reveal that on the interlayer interactions in double layer MoS2 crystals, the emission quantum yield of the A exciton is drastically changed, whereas that of the B exciton remains nearly constant for both single and double layer MoS2 crystals. First-principles density functional theory calculations confirm that a significant charge redistribution occurs in the double layer MoS2 due to the interlayer interactions producing a local electric field at the interfacial region. Analogous to the quantum-confined Stark effect, we suggest that the distinct behavior of the A and B excitons can be explained by a simplified band-bending model.

The dynamic properties of photoinduced alignment and surface relief grating (SRG) formation as a function of excitation wavelength (λex = 454, 488, 514, 532, 568, and 647 nm) are examined using five azobenzene‐derivative polymers, whose absorption spectra are tuned by substituting different electron‐withdrawing groups (CF3, CN, CNCl, NO2, (CN)2). The dynamics sensitively depend on λex. The fastest rate of photoinduced alignment is observed when λex is between λmax of the trans π–π* transition and that of the cis n–π* transition. A model of trans–cis photoisomerization has been developed based on competition between photoexcitation and relaxation, in which the n–π* transition has a faster relaxation pathway than the π–π* transition. Under conditions of adequate absorbance of the trans form at λex, i.e., greater than ${1 \over 2}$Amax, the rate of SRG formation increases at longer λex.