Rh-SP dyad bearing rhodamine (Rh) and spiropyran (SP) moieties was prepared. Reversible photochromic reaction was observed between colorless and nonfluorescent c-Rh-SP and c-Rh-MC with purple color and red fluorescence. Rh-SP can act as a triple chemosensor for Al 3+ , HSO − 3 , and CN − , by absorption and fluorescence spectral changes. The results show colorless solution and orange fluorescence with Al 3+ , red solution and bright orange fluorescence with HSO − 3 , and yellow solution and weak green fluorescence with CN − .

Cyanide is extremely toxic to living organisms including humans. Cyanide prevents oxygen uptake by binding to hemoglobin, myoglobin, and cytochromes. 1,2 It strongly binds to the iron constituent of cytochrome c, prevents transport of electrons from cytochrome c to oxygen, and inhibits mitochondrial energy production.The uses of cyanide are widespread in the chemical industry, gold mining, electroplating, case hardening of iron and steel, photographic applications, and organic chemicals and plastics manufacturing. 3 Moreover, cyanide is found throughout nature in more than 2000 plants and in substantial amounts in certain fruit seeds. 4 In plants, cyanides act as a natural self-defense mechanism against animal predation. Long-term consumption of cyanide-containing foods, such as cassava root or apricot seeds, may lead to cyanide poisoning. The maximum permissive level of cyanide in drinking water was reported at 1.9 μM by the World Health Organization (WHO). 5 Versatile methods of the sensitive and selective detection for cyanide anion to monitor toxic cyanide have been developed. These include colorimetric, fluorimetric, chromatographic, and electrochemical analyses. 6,7 Among those methods for cyanide detection, optical methods based on absorption and fluorescence spectroscopy are relatively simple, inexpensive, and sensitive. 8,9 A number of organic sensors for cyanide anion have been designed and synthesized. Absorption and/or fluorescence spectra of these sensors are changed by forming coordination complex or bonding covalently with cyanide. Compared with other anions, cyanide anion has some characteristic properties, such as its strong nucleophilicity and high binding affinity toward metal ions, and is superior and useful for the development of the sensors. Both covalent bond-based sensors and coordination complex-based sensors have been developed for cyanide detection. 6 Spiropyran derivatives have been extensively studied as typical photochromic molecules. 10,11 The colorless nonfluorescent spiropyran form is converted into colored fluorescent merocyanine form upon ultraviolet (UV) irradiation. The merocyanine form reverts into the spiropyran form upon exposure to visible light or thermal energy. Spiropyran has been reported as a selective, sensitive, and reproducible cyanide anion receptor, based on the covalent bond formation between spiropyran and nucleophilic cyanide anion. 9,12 UV irradiation of colorless spiropyran with cyanide anion results in the formation of yellow-colored merocyanine-cyanide adduct (absorbed at around 420 nm) by nucleophilic addition of cyanide anion to merocyanine (absorbed at around 520 nm) formed by photochemical ring-opening of spiropyran. Colorless spiropyran is reproduced from merocyanine-cyanide adduct by irradiation with visible light.Metalloporphyrins are intense-colored molecules that display a wavelength shift of Soret absorption band with different ligands. 13,14 Many metalloporphyrins are useful cyanide sensors because cyanide has high affinity for many metals in m...

Spiropyran-cored polyamidoamine (PAMAM) dendrons (SP-PAMAMs) were prepared and their solvatochromic and photochromic properties investigated. As with simple merocyanine (MC), MC-PAMAM shows negative solvatochromism. On UV irradiation, colorless SP-PAMAM transforms into colored MC-PAMAM and the reaction occurs a little faster in a more polar solvent. In the dark, MC-PAMAM returns to SP-PAMAM much more slowly in a more polar solvent. On addition of Cu 2+ , the color of SP-PAMAM solution in acetonitrile changes from colorless to orange, whereas neither color change nor absorption spectral changes are observed with the addition of other metal cations.

Porphyrin (Por) has a strong absorption characteristics in the range of sunlight due to a chemical structure of high conjugation and rigidity, good redox properties, and wellestablished synthetic methods. Accordingly, porphyrin-based multicomponent compounds have been investigated in a variety of applications such as artificial light-harvesting antenna, molecular energy storage devices, solar cells, optoelectronic switches, and photodynamic therapy. 1-5Spiropyran (SP) is a typical photochromic molecule performing the reversible interconversion between colorless SP and colored merocyanine (MC). UV-absorbing SP is turned into VIS-absorbing MC by the photochemical ring opening reaction on UV irradiation. Reversely, MC is transformed to SP by the thermal or visible light-induced ring closing reaction. Reversible SP-MC transformation is one of subjects of active research on optical memory and switch in a point of view that the polarity, the excited state energy, or molecular geometry of SP and MC are significantly different. 6-8It is expected that the combination of photoactive Por and photochromic SP could lead to an interesting light-controllable molecular device to control on-off switching of photoinduced processes.In this work, Por-SP dyad linked by ester linkage was prepared by the esterification reaction between carboxylic acid-functionalized porphyrin and hydroxy-functionalized spiropyran and its photoinduced transformation was investigated in tetrahydrofuran and dichloromethane. For Por-SP in tetrahydrofuran, the porphyrin Soret-band maximum is at 416 nm, the porphyrin Q-band maxima are at 515, 550, 590, 645 nm and absorption of spiropyran appears at 350 nm.On irradiation at 350 nm, the absorption spectral changes of Por-SP in tetrahydrofuran were measured with the irradiation time in 5-seccond intervals for 40 sec (Figure 1). Porphyrin characteristic bands at 416 (Soret band), 515, 550, 645 (Q bands) nm remain unchanged, but only the absorbance in 590 nm region corresponding to merocyanine absorption has increased as spiropyran moiety carries out the photochemical ring opening reaction to merocyanine. In tetrahydrofuran, Por-SP is photochemically transformed into Por-MC. These are the same results as reported previously for Porphyrin-Spiropyran dyad linked by methylene linkage.9 As shown in inset of Figure 1, complete conversion from Por-SP into Por-MC takes ~25 sec. Solution colour changes from red to violet. These spectral features are similar to those of diprotonated H 2 Por 2+, formed by the addition of acid to free base Por where two pyrrole imine nitrogens in the core accept two protons.10,11 In the free base Por, four phenyl rings are not conjugated with porphyrin ring because they lie almost perpendicular to the porphyrin plane, whereas in the highly distorted structure of the diprotonated H 2 Por 2+ they rotate towards a more parallel position and have more highly con-

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