Light-Gated Rotation in a Molecular Motor Functionalized with a Dithienylethene Switch

Abstract

A multiphotochromic hybrid system is presented in which a light-driven overcrowded alkene-based molecular rotary motor is connected to a dithienylethene photoswitch. Ring closing of the dithienylethene moiety, using an irradiation wavelength different from the wavelength applied to operate the molecular motor, results in inhibition of the rotary motion as is demonstrated by detailed ¹ H-NMR and UV/Vis experiments. For the first time, a light-gated molecular motor is thus obtained. Furthermore, the excitation wavelength of the molecular motor is red-shifted from the UV into the visible-light region upon attachment of the dithienylethene switch.

Keywords: alkenes; diarylethenes; molecular motors; molecular switches; photochromism.

Scheme 1

a) A full 360° rotary cycle of molecular motors 1 and 2 (note that the isomer generated after 180° rotation is identical to the starting isomer, but has a different viewpoint). b) Representation of light‐gated rotary motion through switching between the open and closed form of the appending DTE moiety.

Figure 1

¹H‐NMR spectra of 2 in CD₂Cl₂. i) Before irradiation; ii) PSS 455 nm; iii) PSS 312 nm; iv) sample from (iii) irradiated with 455 nm; v) sample from (ii) irradiated with 312 nm.

Scheme 2

Photochemical and thermal isomerization steps of hybrid 2.

Figure 2

UV/Vis spectra of hybrid 2 in CH₂Cl₂ (c=1.8×10⁻⁴  m). a) After irradiation with 455 nm (−9 °C) followed by 312 nm (−9 °C) and 528 nm (20 °C). b) After irradiation with 312 nm (20 °C) followed by 455 nm (−9 °C) and 528 nm (20 °C).