Artificial molecular switches and machines that enable the directional movements of molecular components by external stimuli have undergone rapid advances over the past several decades. Particularly, overcrowded alkene-based artificial molecular motors are highly attractive from the viewpoint of chirality switching during rotational steps. However, the integration of these molecular switches into solid-state devices is still challenging. Herein, we present an example of a solid-state spin-filtering device that can switch the spin polarization direction by light irradiation or thermal treatment. This device utilizes the chirality inversion of molecular motors as a light-driven reconfigurable spin filter owing to the chiral-induced spin selectivity effect. Through this device, we found that the flexibility at the molecular scale is essential for the electrodes in solid-state devices using molecular machines. The present results are beneficial to the development of solid-state functionalities emerging from nanosized motions of molecular switches.

An experimental and theoretical study has been carried out to elucidate the nonradiative decay (NRD) and trans(E) → cis(Z) isomerization from the S1 (1ππ*) state of structural isomers of hydroxy methylcinnamate (HMC); ortho-, meta- and para-HMC (o-, m- and p-HMC). A low temperature matrix-isolation Fourier Transform Infrared (FTIR) spectroscopic study revealed that all the HMCs are cis-isomerized upon UV irradiation. A variety of laser spectroscopic methods have been utilized for jet-cooled gas phase molecules to investigate the vibronic structure and lifetimes of the S1 state, and to detect the transient state appearing in the NRD process. In p-HMC, the zero-point level of the S1 state decays as quickly as 9 ps. A transient electronic state reported by Tan et al. (Faraday Discuss. 2013, 163, 321-340) was reinvestigated by nanosecond UV-tunable deep UV pump-probe spectroscopy and was assigned to the T1 state. For m- and o-HMC, the lifetime at the zero-point energy level of S1 is 10 ns and 6 ns, respectively, but it becomes substantially shorter at an excess energy higher than 1000 cm-1 and 600 cm-1, respectively, indicating the onset of NRD. Different from p-HMC, no transient state (T1) was observed in m- nor o-HMC. These experimental results are interpreted with the aid of TDDFT calculations by considering the excited-state reaction pathways and the radiative/nonradiative rate constants. It is concluded that in p-HMC, the trans → cis isomerization proceeds via a [trans-S1 → 1nπ* → T1 → cis-S0] scheme. On the other hand, in o- and m-HMC, the isomerization proceeds via a [trans-S1 → twisting along the C[double bond, length as m-dash]C double bond by 90° on S1 → cis-S0] scheme. The calculated barrier height along the twisting coordinate agrees well with the observed onset of the NRD channel for both o- and m-HMC.

The electronic states and photochemistry including nonradiative decay (NRD) and trans(E) → cis(Z) isomerization of methylcinnamate (MC) and its hydrogen-bonded complex with methanol have been investigated under jet-cooled conditions.

The design of functional molecules is regarded as searching for molecules with desired functionalities in chemical space populated by candidate molecules. Considering the geometric stability of molecules during the search process is crucial for designing realistic molecules. Here, we propose a method for designing functional molecules by exploring chemical space while explicitly accounting for geometric stability based on computational quantum alchemy. The proposed design method allows the simultaneous prediction of functional molecule in the equilibrium structure and its target desired property in an inverse design fashion without preparing the molecular geometries and performing brute-force screening. The applicability of the design method is proven by obtaining molecules with the desired atomization and electronic energies in various chemical spaces: (BF, CO), (CH4, NH3), 18 BN-doped benzene derivatives, and 3.1 × 105 BN-doped phenanthrene derivatives.