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

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 (Forster 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, ...