Photochromic cis-1,2-dithienylethene (DTE) compounds exhibit a reversible interconversion between the open and closed forms under alternating photoirradiation. DTEs could be potentially used for molecular photonic applications because the photochromism of DTEs has advantageous characteristics, such as fatigue resistance, short response time, and reversibility. In particular, the photochromism is thermally irreversible, enabling high fidelity recording of information based on a variety of signals, including fluorescence,[ 2] conductivity, and chiroptical responses. This thermal irreversibility is attributable to the huge groundstate thermodynamic barrier between the open and closed forms of DTEs; this barrier is due to the symmetry constraint as dictated by the Woodward-Hoffmann rule. For instance, the barrier height of cis-1,2-di(3-thienyl)ethene is as high as 46 kcalmol-1. The barrier height is significantly lower in the photoexcited state (i.e., ΔE*<ΔE0 in Figure 1a), thus enabling chromic interconversion. In this context, photochromism can be referred to a process in which photoexcitation provides an excited-state reaction path, thus allowing a smaller energy barrier.
- Electron transfer