“…Random copolymers carrying photochromic spiropyran moieties were synthesized by ATRP. A photosensitive molecule exhibiting a singlet excited state was chosen instead of that with a triplet state, i.e., nitrospiropyrans, because the latter accelerates the photodegradation process . The polymerizable spiropyran molecule was prepared first.…”
Section: Resultsmentioning
confidence: 67%
“…A photosensitive molecule exhibiting a singlet excited state was chosen instead of that with a triplet state, i.e., nitrospiropyrans, because the latter accelerates the photodegradation process. 46 The polymerizable spiropyran molecule was prepared first. The successful synthesis was confirmed by 1 H NMR spectroscopy due to the absence of the peak at 4.26 ppm attributed to the -OH group of the precursor alcohol and the appearance of two new peaks at 5.7 and 6.3 ppm assigned to the protons of the carbon-carbon double bond and a peak at 2.04 ppm which corresponds to the methyl group of the methacryloyl moiety.…”
Multiresponsive spiropyran-based random copolymers were synthesized by atom transfer radical polymerization. The polymers were prepared by the copolymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) with the photochromic monomer 1′,3′,3′-trimethyl-6-methacryloyloxyspiro(2H-1-benzopyran-2,2′-indoline) (SP). The solvatochromic, pH, temperature, and light responsive behavior of the PDMAEMA-co-PSP polymers in solution was monitored by UV/vis spectroscopy. The copolymers exhibited “reverse photochromism” and stabilized the planar zwitterionic form of the chromophore, leading to “negative solvatochromism” upon increasing the polarity of the solvent, in contrast to a poly(methyl methacrylate)-co-PSP analogue which stabilized a nonpolar photoisomer and exhibited negligible sensitivity to the polarity of the surrounding medium, before irradiation. Moreover, the PDMAEMA-co-PSP copolymers exhibited a reversible pH-responsive character in aqueous media; the addition of a strong acid induced the SP-to-merocyanine (MC) isomerization, the formation of [MC−OH]+ and [SP−NH]+ species, and the disappearance of the H-type aggregates, whereas the initial SP moieties were recovered in alkaline media. The chromophore content and the photoinduced MC-to-SP isomerization affected the transition temperature of the PDMAEMA-co-PSP polymers. The lower critical solution temperature (LCST) of the copolymers increased with their content in hydrophilic MC moieties, while the MC-to-SP photoinduced isomerization decreased significantly the LCST due to the hydrophobic character of the SP units. Finally, the copolymers exhibited a first-order photoinduced bleaching of the chromophore units in water and acetonitrile, with a slower decoloration rate in the aqueous medium due to the effective stabilization of the bipolar MC form in the polar environment.
“…Random copolymers carrying photochromic spiropyran moieties were synthesized by ATRP. A photosensitive molecule exhibiting a singlet excited state was chosen instead of that with a triplet state, i.e., nitrospiropyrans, because the latter accelerates the photodegradation process . The polymerizable spiropyran molecule was prepared first.…”
Section: Resultsmentioning
confidence: 67%
“…A photosensitive molecule exhibiting a singlet excited state was chosen instead of that with a triplet state, i.e., nitrospiropyrans, because the latter accelerates the photodegradation process. 46 The polymerizable spiropyran molecule was prepared first. The successful synthesis was confirmed by 1 H NMR spectroscopy due to the absence of the peak at 4.26 ppm attributed to the -OH group of the precursor alcohol and the appearance of two new peaks at 5.7 and 6.3 ppm assigned to the protons of the carbon-carbon double bond and a peak at 2.04 ppm which corresponds to the methyl group of the methacryloyl moiety.…”
Multiresponsive spiropyran-based random copolymers were synthesized by atom transfer radical polymerization. The polymers were prepared by the copolymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) with the photochromic monomer 1′,3′,3′-trimethyl-6-methacryloyloxyspiro(2H-1-benzopyran-2,2′-indoline) (SP). The solvatochromic, pH, temperature, and light responsive behavior of the PDMAEMA-co-PSP polymers in solution was monitored by UV/vis spectroscopy. The copolymers exhibited “reverse photochromism” and stabilized the planar zwitterionic form of the chromophore, leading to “negative solvatochromism” upon increasing the polarity of the solvent, in contrast to a poly(methyl methacrylate)-co-PSP analogue which stabilized a nonpolar photoisomer and exhibited negligible sensitivity to the polarity of the surrounding medium, before irradiation. Moreover, the PDMAEMA-co-PSP copolymers exhibited a reversible pH-responsive character in aqueous media; the addition of a strong acid induced the SP-to-merocyanine (MC) isomerization, the formation of [MC−OH]+ and [SP−NH]+ species, and the disappearance of the H-type aggregates, whereas the initial SP moieties were recovered in alkaline media. The chromophore content and the photoinduced MC-to-SP isomerization affected the transition temperature of the PDMAEMA-co-PSP polymers. The lower critical solution temperature (LCST) of the copolymers increased with their content in hydrophilic MC moieties, while the MC-to-SP photoinduced isomerization decreased significantly the LCST due to the hydrophobic character of the SP units. Finally, the copolymers exhibited a first-order photoinduced bleaching of the chromophore units in water and acetonitrile, with a slower decoloration rate in the aqueous medium due to the effective stabilization of the bipolar MC form in the polar environment.
“…The participation of a triplet state with microsecond lifetime in the isomerization of nitrospiropyrans 18 opens competitive reaction pathways . These side reactions are often irreversible and are responsible for the characteristic photodegradation of nitrospiropyrans. , In particular, the relatively long-lived triplet state encourages the production of significant amounts of singlet oxygen ( 1 Δ g ), 17f,g which, presumably, causes the oxidative degradation of the photochromic species.…”
We have designed and synthesized two photochromic compounds incorporating fused indoline and benzooxazine fragments. Variable-temperature 1H NMR spectroscopy demonstrates that their central [1,3]oxazine ring opens thermally with free energy barriers ranging from 14 to 19 kcal mol(-1). The ring-opened species reverts rapidly to the original isomer and can only be detected after chemical trapping. Specifically, the nucleophilic attack of a hydroxide anion to the indolium cation of the ring-opened species prevents re-isomerization. Laser excitation of both compounds induces the opening of the [1,3]oxazine ring in less than 6 ns with quantum yields up to 0.1. The photoinduced ring opening generates a 4-nitrophenolate chromophore, which absorbs strongly at 440 nm. The photogenerated species reverts to the original form with a lifetime of 22 ns for both compounds. Thus, these transformations can be exploited to interconvert the two isomers of each species with nanosecond switching speeds. Furthermore, thousands of switching cycles can be repeated consecutively without any sign of degradation, even in the presence of molecular oxygen. These processes can be reproduced efficiently in poly(methyl methacrylate) matrixes. Under these conditions, the thermal re-isomerization occurs with biexponential kinetics in submillisecond time scales. In principle, the fast isomerization kinetics and excellent fatigue resistance of both compounds offer the opportunity to modulate rapidly and efficiently a variety of molecular and macroscopic properties. Thus, our molecular design can evolve into the realization of a new family of photochromic compounds and materials with promising photoresponsive character.
“…Thus, virtually all OX is recovered in full after thousands of excitation cycles. The remarkable photochemical stability of OX agrees with the inability of this compound to sensitize efficiently the formation of singlet oxygen, which is responsible in part for the degradation of spiropyrans. 18e,f,− 5 Three consecutive switching cycles of OX (MeCN, 22 °C, 0.1 mM) performed by laser excitation (355 nm, 6 ns, ∼8 mJ) and followed by monitoring the absorbance of IN at 440 nm.…”
[reaction: see text] We have designed a molecular switch based on the photoinduced opening and thermal closing of an oxazine ring. Ultraviolet excitation of this molecule induces the cleavage of a [C-O] bond to form a p-nitrophenolate chromophore in less than 10 ns with a quantum yield of ca. 0.1. The photogenerated isomer reverts thermally to the original oxazine within 50 ns. Our photochromic switch survives more than 3000 excitation cycles without decomposing, even in air-saturated solutions.
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