Multistate Photochromism of 1‑Phenylnaphthalene-Bridged Imidazole Dimer That Has Three Colorless Isomers and Two Colored Isomers

A new type of the bridged imidazole dimer with a 1-phenylnaphthalene moiety that bridges two diphenylimidazole units at the 2- and 2′-positions was synthesized and the photochemical and thermochemical properties were investigated. This molecule shows unique multistate photochromism, in which the stable colorless 1,2′-isomers A and B photochemically isomerize to the colorless 2,2′-isomer through the short-lived biradical with a half-life of 180 ns at 25 °C. The 2,2′-isomer thermally returns to the 1,2′-isomers A and B through the colored isomer at elevated temperatures. The 1,2′-isomers A and B, the 2,2′-isomer, and the colored isomer were isolated, and their molecular structures were determined by X-ray crystallographic analysis. These isomers are stable at room temperature and can be almost fully converted to the 2,2′-isomer by light irradiation. This study serves the useful strategy for the molecular design of a new type of negative photochromic molecules applicable to switch molecular properties by visible light irradiation

Multistate Photochromism of 1‑Phenylnaphthalene-Bridged Imidazole Dimer That Has Three Colorless Isomers and Two Colored Isomers

A new type of the bridged imidazole dimer with a 1-phenylnaphthalene moiety that bridges two diphenylimidazole units at the 2- and 2′-positions was synthesized and the photochemical and thermochemical properties were investigated. This molecule shows unique multistate photochromism, in which the stable colorless 1,2′-isomers A and B photochemically isomerize to the colorless 2,2′-isomer through the short-lived biradical with a half-life of 180 ns at 25 °C. The 2,2′-isomer thermally returns to the 1,2′-isomers A and B through the colored isomer at elevated temperatures. The 1,2′-isomers A and B, the 2,2′-isomer, and the colored isomer were isolated, and their molecular structures were determined by X-ray crystallographic analysis. These isomers are stable at room temperature and can be almost fully converted to the 2,2′-isomer by light irradiation. This study serves the useful strategy for the molecular design of a new type of negative photochromic molecules applicable to switch molecular properties by visible light irradiation

Multistate Photochromism of 1‑Phenylnaphthalene-Bridged Imidazole Dimer That Has Three Colorless Isomers and Two Colored Isomers

A new type of the bridged imidazole dimer with a 1-phenylnaphthalene moiety that bridges two diphenylimidazole units at the 2- and 2′-positions was synthesized and the photochemical and thermochemical properties were investigated. This molecule shows unique multistate photochromism, in which the stable colorless 1,2′-isomers A and B photochemically isomerize to the colorless 2,2′-isomer through the short-lived biradical with a half-life of 180 ns at 25 °C. The 2,2′-isomer thermally returns to the 1,2′-isomers A and B through the colored isomer at elevated temperatures. The 1,2′-isomers A and B, the 2,2′-isomer, and the colored isomer were isolated, and their molecular structures were determined by X-ray crystallographic analysis. These isomers are stable at room temperature and can be almost fully converted to the 2,2′-isomer by light irradiation. This study serves the useful strategy for the molecular design of a new type of negative photochromic molecules applicable to switch molecular properties by visible light irradiation

Multistate Photochromism of 1‑Phenylnaphthalene-Bridged Imidazole Dimer That Has Three Colorless Isomers and Two Colored Isomers

A new type of the bridged imidazole dimer with a 1-phenylnaphthalene moiety that bridges two diphenylimidazole units at the 2- and 2′-positions was synthesized and the photochemical and thermochemical properties were investigated. This molecule shows unique multistate photochromism, in which the stable colorless 1,2′-isomers A and B photochemically isomerize to the colorless 2,2′-isomer through the short-lived biradical with a half-life of 180 ns at 25 °C. The 2,2′-isomer thermally returns to the 1,2′-isomers A and B through the colored isomer at elevated temperatures. The 1,2′-isomers A and B, the 2,2′-isomer, and the colored isomer were isolated, and their molecular structures were determined by X-ray crystallographic analysis. These isomers are stable at room temperature and can be almost fully converted to the 2,2′-isomer by light irradiation. This study serves the useful strategy for the molecular design of a new type of negative photochromic molecules applicable to switch molecular properties by visible light irradiation

Multistate Photochromism of 1‑Phenylnaphthalene-Bridged Imidazole Dimer That Has Three Colorless Isomers and Two Colored Isomers

A new type of the bridged imidazole dimer with a 1-phenylnaphthalene moiety that bridges two diphenylimidazole units at the 2- and 2′-positions was synthesized and the photochemical and thermochemical properties were investigated. This molecule shows unique multistate photochromism, in which the stable colorless 1,2′-isomers A and B photochemically isomerize to the colorless 2,2′-isomer through the short-lived biradical with a half-life of 180 ns at 25 °C. The 2,2′-isomer thermally returns to the 1,2′-isomers A and B through the colored isomer at elevated temperatures. The 1,2′-isomers A and B, the 2,2′-isomer, and the colored isomer were isolated, and their molecular structures were determined by X-ray crystallographic analysis. These isomers are stable at room temperature and can be almost fully converted to the 2,2′-isomer by light irradiation. This study serves the useful strategy for the molecular design of a new type of negative photochromic molecules applicable to switch molecular properties by visible light irradiation

Remarkable Acceleration for Back-Reaction of a Fast Photochromic Molecule

We demonstrate that photochromism based on light-driven reversible C−N single bond cleavage can enable rapid coloration upon UV light irradiation and successive fast thermal back-reaction within tens of microseconds at room temperature. According to Marcus theory, the thermal back-reaction would be accelerated with increasing Δ<i>G</i>⁰, which is closely linked to the decrease in Δ<i>G</i>^‡. We have considered that the Δ<i>G</i>⁰ of the thermal back-reaction could be enlarged by destabilizing the colored species and designed pseudogem-DPI-PI[2.2]PC, with a [2.2]paracyclophane moiety that couples diphenylimidazole and phenanthroimidazole groups. The present study demonstrates that controlling the stability of the biradical state is effective in accelerating the thermal back-reaction for the photochromic [2.2]paracyclophane-bridged imidazole dimer

Remarkable Acceleration for Back-Reaction of a Fast Photochromic Molecule

We demonstrate that photochromism based on light-driven reversible C−N single bond cleavage can enable rapid coloration upon UV light irradiation and successive fast thermal back-reaction within tens of microseconds at room temperature. According to Marcus theory, the thermal back-reaction would be accelerated with increasing Δ<i>G</i>⁰, which is closely linked to the decrease in Δ<i>G</i>^‡. We have considered that the Δ<i>G</i>⁰ of the thermal back-reaction could be enlarged by destabilizing the colored species and designed pseudogem-DPI-PI[2.2]PC, with a [2.2]paracyclophane moiety that couples diphenylimidazole and phenanthroimidazole groups. The present study demonstrates that controlling the stability of the biradical state is effective in accelerating the thermal back-reaction for the photochromic [2.2]paracyclophane-bridged imidazole dimer

Unusual Negative Photochromism via a Short-Lived Imidazolyl Radical of 1,1′-Binaphthyl-Bridged Imidazole Dimer

We have synthesized a new photochromic compound that exhibits unusual negative photo­chromism, in which the stable colored species photo­chemically converts into the metastable colorless species via a short-lived radical. This compound has a 1,1′-bi­naphthyl moiety bridging the two diphenyl­imid­azole units. Its photo­chemical properties were investigated by nanosecond laser flash photolysis. The colored species isomerizes to the colorless species upon exposure to visible light and thermally returns to the original colored species within 20 min at room temperature. Moreover, the photodecoloration reaction proceeds via a short-lived radical with a half-life of 9.4 μs in benzene at room temperature. Both the colored and colorless species show the photo­induced homolytic bond cleavage reaction of the C–N bond between the nitrogen atom of the imid­azole ring and the carbon atom of the 1-position of the 1,1′-bi­naphthyl moiety and that of the C–C bond between each of the carbon atoms of the 2-position of the imid­azole ring, respectively, followed by their formation by rapid radical coupling

Unusual Negative Photochromism via a Short-Lived Imidazolyl Radical of 1,1′-Binaphthyl-Bridged Imidazole Dimer

We have synthesized a new photochromic compound that exhibits unusual negative photo­chromism, in which the stable colored species photo­chemically converts into the metastable colorless species via a short-lived radical. This compound has a 1,1′-bi­naphthyl moiety bridging the two diphenyl­imid­azole units. Its photo­chemical properties were investigated by nanosecond laser flash photolysis. The colored species isomerizes to the colorless species upon exposure to visible light and thermally returns to the original colored species within 20 min at room temperature. Moreover, the photodecoloration reaction proceeds via a short-lived radical with a half-life of 9.4 μs in benzene at room temperature. Both the colored and colorless species show the photo­induced homolytic bond cleavage reaction of the C–N bond between the nitrogen atom of the imid­azole ring and the carbon atom of the 1-position of the 1,1′-bi­naphthyl moiety and that of the C–C bond between each of the carbon atoms of the 2-position of the imid­azole ring, respectively, followed by their formation by rapid radical coupling

Unusual Negative Photochromism via a Short-Lived Imidazolyl Radical of 1,1′-Binaphthyl-Bridged Imidazole Dimer

We have synthesized a new photochromic compound that exhibits unusual negative photo­chromism, in which the stable colored species photo­chemically converts into the metastable colorless species via a short-lived radical. This compound has a 1,1′-bi­naphthyl moiety bridging the two diphenyl­imid­azole units. Its photo­chemical properties were investigated by nanosecond laser flash photolysis. The colored species isomerizes to the colorless species upon exposure to visible light and thermally returns to the original colored species within 20 min at room temperature. Moreover, the photodecoloration reaction proceeds via a short-lived radical with a half-life of 9.4 μs in benzene at room temperature. Both the colored and colorless species show the photo­induced homolytic bond cleavage reaction of the C–N bond between the nitrogen atom of the imid­azole ring and the carbon atom of the 1-position of the 1,1′-bi­naphthyl moiety and that of the C–C bond between each of the carbon atoms of the 2-position of the imid­azole ring, respectively, followed by their formation by rapid radical coupling