Comparison of Complexation-Induced pKa Shifts in the Ground and Excited States of Dyes as Well as Different Macrocyclic Hosts and Their Manifestation in Host-Retarded Excited-Dye Deprotonation

J Phys Chem B. 2017 Dec 21;121(50):11390-11398. doi: 10.1021/acs.jpcb.7b10651. Epub 2017 Dec 11.

Abstract

1-Aminopyrene and 1-naphthylamine-5-sulfonic acid were converted to the putrescine (1,4-diaminobutane)-substituted derivatives (dyes 1 and 2). The diaminobutyl anchor serves as a common binding motive for cation-receptor macrocycles such as cucurbit[n]urils (n = 6-8) and p-sulfonatocalix[4]arene. When protonated, they are prone to undergo a rapid deprotonation in their excited state to result in fluorescence from the unprotonated form (Förster cycle). The deprotonation can be suppressed by complexation with cation-receptor macrocycles, which allows the fluorescence of the locally excited (protonated) state to be dramatically enhanced (factor 12 for dye 1 and 83 for dye 2). This host-retarded excited-dye deprotonation is a direct consequence of the previously established complexation-induced pKa shifts that dyes undergo upon binding to a macrocyclic host. The data set also allows a systematic comparison of complexation-induced pKa shifts in the ground and excited state of a dye. The trends are comparable, which suggests that structural factors, that is, the geometry of the host-guest complexes, determine the magnitude of the shifts. In regard to the magnitude of the absolute pKa shifts on the size of the macrocycles, we observe for dye 2 that the complexation-induced pKa shifts decrease as the portals become larger along the cucurbit[n]uril series.

Publication types

  • Research Support, Non-U.S. Gov't