A novel Pt(II)-diimine complex, [Pt(CN)2(H2dcphen)] (1; H2dcphen = 4,7-dicarboxy-1,10-phenanthroline), was synthesized and its vapochromic shape-memory behavior was evaluated. The as-synthesized amorphous purple solid, [Pt(CN)2(H2dcphen)]·2H2O (1P), exhibited vapochromic behavior in the presence of alcoholic vapors via a transformation to the red, crystalline, porous vaporadsorbed form, 1R ⊃ vapor. The obtained 1R ⊃ vapor complex released the adsorbed vapors upon heating without collapse of the porous structure. The vapor-free, porous 1R⊃ open could detect water or n-hexane vapor, although these vapors could not induce 1P to 1R ⊃ vapor transformation, and 1R ⊃ open could be easily converted to the initial 1P by manual grinding. These results indicate that 1 is a new shape-memory material that functions via formation and collapse of the porous framework with emission change upon vapor-adsorption and grinding; this enables it to exhibit vapor history and ON-OFF switching sensing functions.

A highly methanol-selective vapochromic response has been realized in a Ni -quinonoid complex, [Ni(HL ) ] (H L =4-methylamino-6-methyliminio-3-oxocyclohexa-1,4-dien-1-olate) which exhibits a reversible structural transformation including a coordination geometrical change between the square-planar and octahedral structure by the selective uptake of methanol vapor. This was accompanied by a remarkable color change between purple and orange, as well as temperature-robust spin-state switching in the solid state under ambient conditions. It is remarkable that the properties are derived by the fine structural modification of the quinonoid ligand such as methyl or ethyl analogues. Such a system has high potential for applications in memory devices as well as chemical sensors and smart responsive materials.

A highly methanol‐selective vapochromic response has been realized in a NiII‐quinonoid complex, [Ni(HLMe)2] (H2LMe=4‐methylamino‐6‐methyliminio‐3‐oxocyclohexa‐1,4‐dien‐1‐olate) which exhibits a reversible structural transformation including a coordination geometrical change between the square‐planar and octahedral structure by the selective uptake of methanol vapor. This was accompanied by a remarkable color change between purple and orange, as well as temperature‐robust spin‐state switching in the solid state under ambient conditions. It is remarkable that the properties are derived by the fine structural modification of the quinonoid ligand such as methyl or ethyl analogues. Such a system has high potential for applications in memory devices as well as chemical sensors and smart responsive materials.

We synthesized a carboxy-functionalized Pt(ii)–terpyridine complex that exhibits vapochromic behavior that is switchable via protonation/deprotonation of the carboxy group.

A luminescent Pt(ii) complex with potassium ions was successfully synthesized and its coordination-based vapochromic behavior was investigated.

The luminescent Cu­(I) coordination polymers [Cu2I2(m,m′-bpy)] n (CuI- m; m,m′-bpy = m,m′-bipyridine; m = 3, 4) were successfully synthesized by the solvent-free thermal reaction of the metal salt CuI with the organic linkers m,m′-bpy. Powder X-ray diffraction analysis revealed that CuI-3 was immediately formed when a mixture of CuI and 3,3′-bpy was ground in a mortar at room temperature (20 °C). In contrast, a temperature >120 °C was required to synthesize the CuI-4 isomer, probably because of the higher melting point of the 4,4′-bpy linker. Although excess bpy linker was necessary to afford the CuI- m in high yield, the quantitative synthesis, without any purification processes, was successfully achieved by simple heating at 140 °C, whereby the excess bpy linker was thermally removed by evaporation. Single crystal X-ray structural analysis indicated that in CuI-3 the dinuclear {Cu2I2} rhombic cores were bridged by 3,3′-bpy linkers. A similar structure was observed for CuI-4; however, the intermolecular π–π stacking that was effective in CuI-4 was suppressed in CuI-3 because of the twisted configuration of the two pyridyl rings of the 3,3′-bpy linker. CuI-3 exhibited bright green emission with the maximum (λem) at 519 nm and a high emission quantum yield (Φ = 0.58) in the solid state at room temperature, in contrast to the weak red emission of CuI-4 (λem = 653 nm, Φ < 0.01). Emission decay analysis and density functional theory calculations suggested that the CuI- m emissions could be attributed to the delayed fluorescence from the metal-to-ligand charge-transfer excited state effectively mixed with the halide-to-ligand charge-transfer excited state.

A novel Pt­(II) diimine complex, [Pt­(CN)2­(H2dpcpbpy)] (1, H2dpcpbpy = 4,4′-di­(p-carboxyphenyl)-2,2′-bipyridine), was synthesized, and its vapochromic behavior was investigated. The y ellow a morphous form of 1, 1-Ya, transformed into the porous o range c rystalline form, 1-Oc, upon exposure to ethanol vapor. This behavior is similar to that of the previously reported complex, [Pt­(CN)2(H2dcphen)] (2, H2dcphen = 4,7-dicarboxy-1,10-phenanthroline). X-ray diffraction study showed that 1-Oc possessed similar but larger porous channels (14.3 × 8.6 Å) compared to the r ed c rystalline form of 2, 2-Rc (6.4 × 6.8 Å). Although the porous structure of 2-Rc was retained after vapor desorption, that of 1-Oc collapsed to form the o range a morphous solid, 1-Oa. However, the orange color was unchanged in this process. The initial color was recovered by grinding 1-Oa and 2-Rc. These vapor-writing and grinding-erasing functions can be applied to both in situ vapor sensing and vapor-history sensing, i.e., sensors that can memorize the existence of previous vapors. A notable difference was observed for humid air sensitivity; the orange emission of 1-Oa was largely unaffected upon exposure to humid air, whereas the red emission of 2-Rc was significantly affected. The lesser sensitivity of 1-Oa toward humidity is important for stable vapor-history sensor applications.

A luminescent Pt(ii) complex [Pt(CN)(Hdpbpy)] (1P; Hdpbpy = 2,2'-bipyridine-4,4'-diphosphonic acid) bearing a phosphonic-acid-functionalized bipyridine ligand was successfully synthesized and its unique two-way vapochromic behaviour investigated. X-ray structure analyses of both the anhydrous 1P and penta-hydrated 1P·5H2O phases clearly reveal the activation of intermolecular PtPt interactions through the adsorption of water vapour. Emission spectroscopy reveals that the penta-hydrated 1P·5H2O complex exhibits an orange emission at 585 nm that shifts in two directions, to a blue-green emission at 469 nm by drying at 100 °C or to a red emission at 701 nm by drying under vacuum at room temperature. Thermogravimetric analyses and powder X-ray diffraction studies clearly reveal that anhydrous 1P, with negligible intermolecular PtPt interactions, is formed by drying at 100 °C whereas the monohydrate 1P·H2O phase, with effective PtPt interactions, is formed by drying under vacuum.