Reversible Switching of Tb(III) Emission by Sensitization from 2,3-Dihydroxynaphthalene in an Isothermally Reversible Ionic Liquid

A reversible room-temperature ionic liquid (ILO) was prepared by the addition of CO2 to an equimolar mixture of hexylamidine (AD) and butylamine (AN). The ILO and AD/AN mixture were cycled repeatedly by alternating the passage of CO2 and N-2 gases through the liquid. The ILO was utilized to sensitize very efficiently energy transfer to and emission by Tb(III) ions when 2,3-dihydroxynaphthalene (DHN) was irradiated. The emission was nearly completely quenched in the AD/AN mixture. The process described here is unique in its use of CO2 and N-2 to switch on and off the emission by a lanthanide ion, Tb(III) in this case. In the corresponding amidinium dithiocarbamate ionic liquid (ILS), no appreciable Tb(III) emission was found due to quenching of the excited singlet state of DHN by thio groups. The ILS was not reconverted to the AD/AN mixture upon adding N-2; N-2 bubbling did not result in the displacement of CS2.