Hyperchromisity and molecular recognition of a novel modified β-cyclodextrin tethering with phenylaminoazobenzene.

A modified β-cyclodextrin (1) tethered with a phenylaminoazobenzen moiety has been synthesized for the purpose of developing a new guest-responsive color-change chemosensor. When the solution became acidic, 1 changed color from yellow to purple due to a structural change of the dye moiety from the azo form to the azonium one by protonation on the azo group. However, the pH titration curve of 1 was affected by the presence of the guest, as shown by the fact that the curve in the acidic region shifted to the neutral side by the presence of 1-adamantanol. This suggests that 1 has a potential to show a guest-induced absorption variation under the acidic condition. Upon guest addition at pH 0.61 at the concentration of 1 with 1 × 10(-5) M, 1 showed a colorless-to-color change. Such hyperchromisity in the absorption spectrum of 1 is associated with a guest-induced conformational change of the dye moiety from inside to outside of the CD cavity, and is used for molecular sensing. Among various guests, 1 was found to be highly sensitive to a steroidal guest having a C12 hydroxyl group in the framework, such as ursodeoxycholic acid and lithocholic acid in an acidic aqueous solution.