Tetramethylcucurbit[6]uril-triggered fluorescence emission and its application for recognition of rare earth cations

The host-guest interaction between tetramethylcucurbit[6]uril (TMeQ[6]) and 2-(4-methoxyphenyl)-1H-imidazo[4,5- f][1,10]phenanthroline hydrochloride salt (guest 1) has been investigated. H-1 NMR results have confirmed the formation of an encapsulated complex, and fluorescence titration implies an interaction ratio of 1:1 with a moderate association constant of K-a = 4.0 x 10(6) L mol(-1). The triggered fluorescence emission of guest 1 by TMeQ[6] has been developed to achieve a supramolecular probe capable of recognizing La3+ and Ce3+ through a dramatic decrease in fluorescence intensity, whereas there is minimal difference upon the introduction of Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Er3+, or Tm3+. Combined evidence from H-1 NMR, IR, and fluorescence titration supports coordination of the inclusion complex to La3+ and Ce3+, with association constants of 1.1 x 10(4) L mol(-1) and 1.0 x 10(4) L mol(-1), respectively. The linear decrease in fluorescence intensity in response to different concentrations of La3+ or Ce3+ gives a low limit of detection(LOD) of 1.1 x 10(-8) mol L-1. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.