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Investigation of an Acid–Base and Redox Molecular Switch: From Bulk to the Single‐Molecule Level
Author(s) -
AlKaysi Rabih O.,
Bourdelande José Luis,
Gallardo Iluminada,
Guirado Gonzalo,
Hernando Jordi
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700236
Subject(s) - deprotonation , protonation , guanidine , chemistry , fluorescence , molecular switch , molecule , fluorophore , moiety , photochemistry , quenching (fluorescence) , stereochemistry , ion , organic chemistry , physics , quantum mechanics
In this work we investigate a new fluorescent molecular switch based on the interconversion between the fluorescent zwitterionic form (ZW1) and the non‐fluorescent anionic state (MC2) of a spirocyclic Meisenheimer complex of 1,3,5‐trinitrobenzene. Density functional theory molecular orbital calculations reveal that photo‐induced electron transfer from a guanidine group to the trinitrocyclohexadiene fluorophore of the complex quenches the emission from MC2. Protonation, as well as coordination of other Lewis acids to the guanidine group, suppress the quenching mechanism and allow the complex to fluoresce. In agreement with the calculations, reversible on–off fluorescence switching of the ZW1–MC2 bulk system occurs by protonation–deprotonation of the guanidine moiety upon acid–base addition. Interestingly, spectroelectrochemical ensemble measurements show that switching of the ZW1–MC2 pair can also be attained electrochemically, thus unraveling the versatile functioning of this system. The ultimate limit of monitoring the reversible on–off operation of individual switch molecules is reached by means of single‐molecule fluorescence spectroscopy, which demonstrates the potential of the ZW1–MC2 system to be used as a true single‐molecule switch on the nanometer scale.