Characterization of the Thermal and Photoinduced Reactions of Photochromic Spiropyrans in Aqueous Solution

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.

Water‐Soluble Spiropyrans with Inverse Photochromism and Their Photoresponsive Electrostatic Self‐Assembly

“…The kinetic data were fitted with the program DynaFit [59] according to the mechanistic models presented in Scheme 5. Protonation of the SP form as in the literature [50,60] couldn ot be observed at pH 3. Protonation of the SP form as in the literature [50,60] couldn ot be observed at pH 3.…”

“…[15] These distinct properties are the reason fort he extensive applications of spiropyrans in supramolecular complexes, [16][17][18][19][20][21][22][23][24][25] nanoparticle functionalization, [22][23][24][25] smart polymer materials, [26][27][28][29] nanocarriers, [31][32][33][34][35][36][37] and biochemical systems. The hydrolysis will be compared to the one of water-soluble spiropyrans substituted with aq uaternary ammoniumg roup recently investigated by Hammarson et al [50] Hence,w ep resent af undamental study demonstratingt he features and possibilities of self-assembly with water-soluble spiropyrans, as ap roof of concept, and with future potential in solar energy conversion,nanotechnology,a nd medicine. [51][52][53][54] In the latter case, the sulfonate group is almosta lwaysi ntroduced by alkylation of the indoline nitrogen via as ultone.…”

Photoswitchable phospholipid FRET acceptor: Detergent free intermembrane transfer assay of fluorescent lipid analogs

“…Repeated photoswitching cycles did not significantly alter the initially observed switching characteristics. Additionally, photoswitching was also not associated with significant photobleaching, consistent with previous reports on other spiropyran compounds 21, 22 .

Figure 4UV dependent photoswitching of N -nitroBIPS-DPPG fluorescence. The fluorescence (λex = 543 nm, λem = 600 nm) of a DOPC/ N -nitroBIPS-DPPG (9:1) dispersion (50 μM) was recorded during alternating (5 sec intervals) UV (340 nm) and green light (543 nm) exposure (red line) and during continuous green light (543 nm) irradiation (blue line).

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ATRP-based synthesis and characterization of light-responsive coatings for transdermal delivery systems

“…The hydrolysis of SP derivatives back to the initial aldehydes used in the synthesis of these compounds is a known phenomenon during the photo-degradation process of SP [40]. The hydrolysis reaction of the SP moieties in the membranes to the aldehyde under basic conditions was used to determine the incorporated amount of SP in the membranes after the post-polymerization modification.…”

“…The resistance to photo degradation of SP is strongly dependent on the chemical surrounding of the dye. More electron withdrawing groups are expected to stabilize the charged MC form to prevent photo degradation [40]. In the comparably thick pHEMA layer the SP moieties have predominantly pHEMA in the surrounding, whereas in the thin pHEMA layer also the polyester membranes are present influencing the stability of the SP upon UV-irradiation.…”