Alkyl-substituted spiropyrans: electronic effects, model compounds and synthesis of aliphatic main-chain copolymers

Schmidt, Simon B.; Kempe, Fabian; Brügner, Oliver; Walter, Michael; Sommer, Michael

doi:10.1039/c7py00987a

Cited by 18 publications

(26 citation statements)

References 46 publications

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“…The theoretically computed energies agree with the experimentally observed forms and moreover underline the increased stabilities of the Z - and E -isomers through significantly higher thermal barriers than in the deprotonated states. Additionally, in contrast to conclusions drawn earlier regarding the protonation of spiropyrans, 33 , 34 , 36 , 37 , 45 , 46 , 48 theory suggests that the protonation of the indolinic nitrogen leads to barrierless proton transfer to the phenolate. Hence, even if an acid is strong enough to protonate the indolinic nitrogen, spontaneous ring opening to the Z -( N ) MCH + form would make such a protonation transient at most.…”

Section: Discussioncontrasting

confidence: 73%

“…Indeed, this is the case that is apparent in the blue shifted shoulder due to the Z -( N ) MCH + form in spectra reported earlier. 37 …”

Section: Resultsmentioning

confidence: 99%

“… 36 Later, Schmidt et al noted the formation of the protonated E -merocyanine in ethanol upon addition of trifluoroacetic acid. 37 Collectively, these reports indicate that ring opening to the stable protonated E -merocyanine occurs upon protonation. However, over two decades ago, Zhou and co-workers reported a species “Y” while investigating the pH dependence of the negative photochromism of a 6′,8′-dinitrospiropyran, for which the merocyanine form is most stable even when unprotonated.…”

Section: Introductionmentioning

confidence: 93%

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Proton-Stabilized Photochemically Reversible E/Z Isomerization of Spiropyrans

et al. 2018

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Spiropyrans undergo Cspiro–O bond breaking to their ring-open protonated E-merocyanine form upon protonation and irradiation via an intermediate protonated Z-merocyanine isomer. We show that the extent of acid-induced ring opening is controlled by matching both the concentration and strength of the acid used and with strong acids full ring opening to the Z-merocyanine isomer occurs spontaneously allowing its characterization by 1H NMR spectroscopy as well as UV/vis spectroscopy, and reversible switching between Z/E-isomerization by irradiation with UV and visible light. Under sufficiently acidic conditions, both E- and Z-isomers are thermally stable. Judicious choice of acid such that its pKa lies between that of the E- and Z-merocyanine forms enables thermally stable switching between spiropyran and E-merocyanine forms and hence pH gating between thermally irreversible and reversible photochromic switching.

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Section: Discussioncontrasting

confidence: 73%

“…Indeed, this is the case that is apparent in the blue shifted shoulder due to the Z -( N ) MCH + form in spectra reported earlier. 37 …”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 93%

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Proton-Stabilized Photochemically Reversible E/Z Isomerization of Spiropyrans

et al. 2018

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“…At the same time, Zhou and co-workers assigned an intermediate observed upon protonation of 6 0 ,8 0 -dinitrospiropyran to a protonated form with a broken C spiro -O bond that had not yet achieved planarisation (''species X''). 87 The proposed intermediacy of the protonated cisoid form was supported by Shiozaki shortly thereafter, 88 who showed a better-defined response to protonation of spiropyran in ethanol with sulfuric acid than with the more commonly used trifluoroacetic 68,69,[89][90][91][92][93][94][95][96][97] and hydrochloric acids. 18,[98][99][100][101][102][103][104][105][106][107][108][109] These observations indicate that distinct protonated cisoid and transoid structures differ in pK a .…”

Section: Acidochromism and Ph-gated Z/e-isomerization Of Spiropyransmentioning

confidence: 96%

The evolution of spiropyran: fundamentals and progress of an extraordinarily versatile photochrome

2019

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“…In comparison to phenyl groups, aliphatic substituents facilitate the formation of the MCH + form due to their inductive effect. [32] Substituent effects of spiropyrans have also been the subject of detailed theoretical studies. [33,34] Brügner et al used density functional theory to predict Hammett parameters, which subsequently were used to estimate the internal energy ΔU of SP→ MC conversion for pairs of substituents at the N-and 6-position in the gas phase ( Figure 2).…”

Section: Effect Of Sp Substituents On Sp/mc Equilibrium In Solutionmentioning

confidence: 99%

Substituent Effects Control Spiropyran–Merocyanine Equilibria and Mechanochromic Utility

Sommer

2020

Macromol. Rapid Commun.

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From a microscopic point of view, CC bond cleavage produces radicals which may undergo secondary reactions that further destabilize polymeric materials. Thus, for a long time, such mechanicallyinduced bond scission and degradation has been treated in negative context, as these reactions occurred in an uncontrolled way, at undefined positions at the polymer chain and usually caused property profiles of lower quality. The view on mechanically-induced chemical reactions has meanwhile changed, with mechanochemistry [6,7] being nowadays a vital field that aims at exploiting mechanical force as a form of energy to trigger chemical reactions, which yield product distributions that may or may not differ compared to heat-and light-induced reactions. [8] A prime example in the area of polymer mechanochemistry includes mechanically induced metal-ligand bond scission [9] that gives rise to mechano-catalysis, as pioneered by the Sijbesma group. [10,11] Work by Hickenboth et al. has investigated a force-induced pericyclic ring opening reaction which furnished different product distributions compared to what is obtained according to the Woodward-Hoffman rules. [12] Polymers are ideal for this purpose as stress transduction to the molecular level is easily achieved using solution sonication or bulk mechanical testing. If a mechanically-induced reaction leads to changes in optical properties, the material is termed mechanochromic. The structural unit undergoing optical changes upon mechanical activation is called mechanophore. [13] In 2001, Tipikin et al. observed that grinding a spiropyran (SP) small molecule produces the corresponding merocyanine (MC) and thus a color change. [14] The force-induced SP→MC isomerization by using polymers with SP units covalently incorporated at their mid points was pioneered by Moore et al. using sonication and later on by Sottos et al. using classical stress-strain experiments of bulk specimens. [13,15] Their pioneering works initiated a large number of studies, not only in the area of SP containing polymers but also related to the development of other mechanophores, in the areas of mechanochemistry and mechanochromic polymers. Since then SPs are popular mechanophores despite their multiple isomers and conformers. [16-19] It is interesting to note that the two positions of polymer linkage at SP, which are meanwhile considered most efficient for mechanoactivation, have been used by Smeets et al. as early as 1974 to Spiropyran (SP) derivatives can be converted into the colored merocyanine (MC) form using a variety of triggers. Optical switching by light for memories and dynamic systems is long known. Recently, mechanical force has been reported as an additional stimulus that converts SP into MC. SP-based mechanochromic systems are especially interesting for polymer scientists, as the covalent attachment of polymer chains is ideal to transduce force to the SP level. Whether such materials are investigated to better understand fundamental processes or long standing questions in polymer science, to ...

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Alkyl-substituted spiropyrans: electronic effects, model compounds and synthesis of aliphatic main-chain copolymers

Abstract: This work reports on the isomerisation behaviour of alkylated spiropyrans and aliphatic main chain spiropyran copolymers.

Cited by 18 publications

References 46 publications

Proton-Stabilized Photochemically Reversible E/Z Isomerization of Spiropyrans

Proton-Stabilized Photochemically Reversible E/Z Isomerization of Spiropyrans

The evolution of spiropyran: fundamentals and progress of an extraordinarily versatile photochrome

Substituent Effects Control Spiropyran–Merocyanine Equilibria and Mechanochromic Utility

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