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Characterization of the thermal and photoinduced reactions of photochromic spiropyrans in aqueous solution.

Hammarson M, Nilsson JR, Li S, Beke-Somfai T, Andréasson J - J Phys Chem B (2013)

Bottom Line: The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory.The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction.Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology , 412 96 Göteborg, Sweden.

ABSTRACT
Six water-soluble spiropyran derivatives have been characterized with respect to the thermal and photoinduced reactions over a broad pH-interval. A comprehensive kinetic model was formulated including the spiro- and the merocyanine isomers, the respective protonated forms, and the hydrolysis products. The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory. The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction. Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

No MeSH data available.


Structures of the closed spiro (SP) forms of the spiropyran derivativesstudied in this work.
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fig1: Structures of the closed spiro (SP) forms of the spiropyran derivativesstudied in this work.

Mentions: The primary objective of this work has been to investigate in detailthe various thermal, acido- and photochromic processes for the spiropyranderivatives shown in Figure 1. Compounds 1–4 have a nitro substituent in the 6-positionof the benzopyran moiety (C6, see Scheme 1 for labeling of relevant atoms discussed in the text). Thesecompounds differ in the number of methylene units in the aminoalkyl-derived“tail” attached to the indoline nitrogen NI (three or five), as well as the number of methyl groups on the aminonitrogen NA (two or three). Compounds 5 and 6 are equipped with a quaternary amine via a propyl tail andcome with an aldehyde and a cyano group on C6, respectively.The main reason for using different substituents on the benzopyranring was to vary the pKa-value of thephenolic OH group of the protonated MC isomer (MCH+, seeScheme 1).61 A moreelectron withdrawing substituent is expected to stabilize the negativelycharged oxygen OPh of the nonprotonated MC isomer and,hence, decrease the pKa-value.62 Moreover, the variation of the substituentsat both the benzopyran ring and the indoline nitrogen NI effects several other thermal and photoinduced processes, as willbe described in detail below. In the following sections, the experimentalresults (spectra, kinetic traces, etc.) will be shown only for 1, whereas the corresponding data for 2–6 is collected in the Supporting Information.


Characterization of the thermal and photoinduced reactions of photochromic spiropyrans in aqueous solution.

Hammarson M, Nilsson JR, Li S, Beke-Somfai T, Andréasson J - J Phys Chem B (2013)

Structures of the closed spiro (SP) forms of the spiropyran derivativesstudied in this work.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814652&req=5

fig1: Structures of the closed spiro (SP) forms of the spiropyran derivativesstudied in this work.
Mentions: The primary objective of this work has been to investigate in detailthe various thermal, acido- and photochromic processes for the spiropyranderivatives shown in Figure 1. Compounds 1–4 have a nitro substituent in the 6-positionof the benzopyran moiety (C6, see Scheme 1 for labeling of relevant atoms discussed in the text). Thesecompounds differ in the number of methylene units in the aminoalkyl-derived“tail” attached to the indoline nitrogen NI (three or five), as well as the number of methyl groups on the aminonitrogen NA (two or three). Compounds 5 and 6 are equipped with a quaternary amine via a propyl tail andcome with an aldehyde and a cyano group on C6, respectively.The main reason for using different substituents on the benzopyranring was to vary the pKa-value of thephenolic OH group of the protonated MC isomer (MCH+, seeScheme 1).61 A moreelectron withdrawing substituent is expected to stabilize the negativelycharged oxygen OPh of the nonprotonated MC isomer and,hence, decrease the pKa-value.62 Moreover, the variation of the substituentsat both the benzopyran ring and the indoline nitrogen NI effects several other thermal and photoinduced processes, as willbe described in detail below. In the following sections, the experimentalresults (spectra, kinetic traces, etc.) will be shown only for 1, whereas the corresponding data for 2–6 is collected in the Supporting Information.

Bottom Line: The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory.The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction.Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology , 412 96 Göteborg, Sweden.

ABSTRACT
Six water-soluble spiropyran derivatives have been characterized with respect to the thermal and photoinduced reactions over a broad pH-interval. A comprehensive kinetic model was formulated including the spiro- and the merocyanine isomers, the respective protonated forms, and the hydrolysis products. The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory. The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction. Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation.

No MeSH data available.