The fluorescence properties of cationic rhodamine B in the gas phase

Studying the photophysical properties of molecules in the gasphase can be advantageous, because it reduces the complexity of the system examined by eliminating effects due to theinteractions between the molecule of interest and other species present in the local environment, including those with the solvent itself. Here, we report on theintrinsic properties of gaseous protonated rhodamine B (RBH+), a well-known xanthene-based dye. Protonated rhodamine B was transferred into the gas phase using electrospray ionization (ESI) and isolated in a quadrupole ion trap (QIT) mass spectrometer, which has been modified to enable laser-induced fluorescence spectroscopy of trapped ions. The gas-phase fluorescence excitation and emission spectra of RBH+show maxima (λex (max) = 531 nm and λem (max) = 542 nm, respectively)that lie at higher energy than those of RBH+ in solution. The fluorescence lifetime of gaseous RBH+ is 5.97 ±  0.12 ns, which is significantly longer than that of solution-phase rhodamine B. Gaseous rhodamine B is signficiantly brighter than monoethylamino rhodamines such as gaseous rhodamine 6G. Knowledge of the intrinsic photophysical properties of chromophores, such as those presented here for rhodamine B, will enable a better understanding of how the local environment of the chromophore modulates its properties.

► Gaseous protonated rhodamine B (RBH+) isolated using ESI mass spectrometry. ► Intrinsic fluorescence properties of mass-selected RBH+measured. ► Fluorescence excitation and emission spectra and lifetimes compared with solution. ► RBH+ is ∼2 times as bright as gaseous rhodamine G.