Bridged-Imidazole Dimer Exhibiting Three-State Negative Photochromism with a Single Photochromic Unit

Abstract

Photochromic molecules that can exhibit multiple states of photochromism in a single photochromic unit are considered more attractive than traditional bistable photochromic molecules because they can offer more versatility and control in photoresponsive systems. We have synthesized a negative photochromic 1-(1-naphthyl)pyrenyl-bridged imidazole dimer (NPy-ImD) that has three different isomers: a colorless isomer, 6MR, a blue-colored isomer, 5MR-B, and a red-colored isomer, 5MR-R. NPy-ImD can interconvert between these isomers via a short-lived transient biradical, BR, upon photoirradiation. 5MR-R is the most stable isomer, and the energy levels of 6MR, 5MR-B, and BR are relatively close to each other. The colored isomers 5MR-R and 5MR-B are photochemically isomerized to 6MR via the short-lived BR upon irradiation with blue light and red light, respectively. The absorption bands of 5MR-R and 5MR-B are well separated by more than 150 nm, with a small overlap, which means they can be selectively excited with different light sources, visible light for 5MR-R and NIR light for 5MR-B. The colorless isomer 6MR is formed from the short-lived BR through a kinetically controlled reaction. 6MR and 5MR-B can then be converted to the more stable isomer 5MR-R through a thermodynamically controlled reaction, which is facilitated by the thermally accessible intermediate, BR. Notably, 5MR-R photoisomerizes to 6MR when irradiated with CW-UV light, whereas it photoisomerizes to 5MR-B by a two-photon process when irradiated with nanosecond UV laser pulses.

Dual Emulsion Fabrication Approach to Core–Shell Microspheres for Polymer Laser Direct Writing

“…Most importantly, the pattern and text fabricated by LDW are resistant and durable and do not easily fade or blur. 7−9 When polymers are irradiated with a laser for a short period of time, their surfaces undergo carbonization, 10 foaming 11 or photochromism, 12,13 resulting in the formation of patterns in various colors. 14,15 However, it is difficult for polymers to absorb lasers of different wavelengths because of their inherent transparency.…”

“…When polymers are irradiated with a laser for a short period of time, their surfaces undergo carbonization, foaming or photochromism, , resulting in the formation of patterns in various colors. , However, it is difficult for polymers to absorb lasers of different wavelengths because of their inherent transparency . Conventionally, the main solution is to incorporate a laser absorber into the polymer matrix .…”

All-visible-light-driven stiff-stilbene photoswitches

“…Meanwhile, new scaffolds of photoswitches have emerged in recent years responding to visible light, such as indirubin, 34 (thio-)indigobased photoswitches developed by Dube, 32,35,36 imino indolinone, 37 and imidazole-dimer-based photoswitches. [38][39][40] Stiff-stilbenes, 41 a prominent class of photoswitches derived from stilbene that feature a fused ve-membered ring, have shown distinct advantages in various research areas, such as supramolecular assemblies, [42][43][44][45][46][47] molecular force probes, [48][49][50] photoresponsive receptors, 51-54 ligands, 55 and light emitting materials, 56 owing to their large geometric change, robust switching behavior, and excellent bi-thermostability (P-type). These alkenes are also the basis of light-driven rotary molecular motors.…”

“…Meanwhile, new scaffolds of photoswitches have emerged in recent years responding to visible light, such as indirubin, 34 (thio-)indigo-based photoswitches developed by Dube, 32,35,36 imino indolinone, 37 and imidazole-dimer-based photoswitches. 38–40…”

A Cu 2+ triggered reversible photochromic system: the structure photochromic response relationship study and potential applications

“…Therefore, salicylaldehyde or 2-pyridine carboxaldehyde derivatives which have an ortho-coordination site were employed for coupling with rhodamine B hydrazide to construct photochromic system in most of the follow-up studies [19][20][21][22][23][24][25][26]. Although great progress has been made in the development of photochromic materials [27][28][29], the structure photochromic response relationship (SPRR) of RhBHH-based photochromic materials are still blurry. In addition, due to the strong chelation of the above RhBHH derivatives, no photochromic phenomenon would be observed or too much bleaching time would be needed when Cu 2+ was used as the trigger [18].…”