Thermally Activated Photochromism: Realizing Temperature‐Gated Triphenylethylene Photochromic Materials

Abstract

Photochromic materials have drawn enormous attention for their potential applications in optical memory storage and photoswitchable molecular devices. Although great achievements for photochromic materials have been fulfilled, it is still a big challenge to realize gated photochromism for ready tunable photochromic properties. In previous studies, rare examples of gated photochromism are reported. Herein, three triarylethylene derivatives FTrPE‐oI, ClTrPE‐oI and BrTrPE‐oI with reversible thermally activated photochromic characteristics are designed and synthesized, whose crystalline powders show no photochromism until thermally activated treatments to relative temperature. Temperature acts as a gate to switch the photochromic properties by switching the aggregation state from crystalline to melted amorphous. With this progress, a broader structural realm becomes accessible for gated photochromic materials, which can now be synthetically tailored for advanced future applications, e.g., in research on gated molecular machines and switches, in studies of photoisomerization mechanisms, or in the generation of thermal tracing materials. To showcase the potential of these distinct thermally activated photochromic materials, their applications in encrypted thermal printing, thermal trace monitoring as well as multi‐level anticounterfeiting are demonstrated, in addition to a comprehensive photochemical study of all compounds.

Effect of cis/trans isomerization on the photochromic performances of triphenylethylene

“…The photochromic processes of TP , TP-F , TP-Cl and TP-Br in the solid state are obviously faster than those in solution. Rapid solid-state photochromism may be caused by two factors: one is that the intramolecular motion (rotation and vibration) of twisted structures in the solid state is limited, which makes it easier for cyclized isomers to stabilize; 36,37 the other is the limited penetration depth of light stimulation, and photochromism mainly occurs on the thin outer surface. 38 Similar to their solution state, the color change order under UV irradiation is still TP-Br ≈ TP-Cl > TP-F > TP .…”