Kinetic characterization of spiropyrans in aqueous media

Abstract

Detailed kinetic investigations of the most common photoswitchable spiropyran, 6-nitro-BIPS, reveal that hydrolytic decomposition of its merocyanine isomer limits its utility in aqueous buffer; however, simple replacement of the 6-nitro substituent with an 8-carboxylate yields a BIPS photoswitch that is potentially better suited for biological applications.

Switching Properties of a Spiropyran–Cucurbit[7]uril Supramolecular Assembly: Usefulness of the Anchor Approach

“…Similar kinetics with a biexponential "rise and decay" behaviour have been reported for related spiropyrans. [63,64] In our case this fitting yielded a rise time constant of  1 = 6.5 h, corresponding to a rate constant of k 1 = 4.3 × 10 5 s…”

“…In the following the acido-and photochromic behaviour of spiropyran 1 as well as its hydrolytic stability [63] will be discussed in detail. The corresponding processes are illustrated in Scheme 1.…”

“…For example, this may be a problem for the storage capability of the merocyanine during long-term experiments in water. The hydrolysis is known to be initiated by nucleophilic attack at the ene-iminium cation, which is followed by a retro-aldol reaction, leading to Fischer's base (6) and 4-nitrosalicyladehyde (7); [63] see structures in Scheme 1.…”

“…7 h was determined at pH 7. [63] With general character, the discussed hydrolytic instability is one of the limiting factors for the application of spiropyrans in aqueous medium. For example, this may be a problem for the storage capability of the merocyanine during long-term experiments in water.…”

Dynamics of a photochromic spiropyran under aqueous conditions

“…We investigated a spiropyran with an enhanced water solubility ( Figure 1) due to a pyridinium structure in the right part of the molecule that could be switched between the closed spiropyran and the open merocyanine form numerous times and also appears to be stable in solution for several weeks in contrast to spiro compounds used in earlier experiments where a decomposition took place within hours [9,10]. Our time-resolved measurements reveal that the opening reaction takes place within 1.6 ps via the S1 state, whereas the closing reaction is accomplished within 25 ps after relaxation of the excited state via the merocyanine ground state.…”