We have studied the gas-phase laser-induced fluorescence of an ensemble of buffer gas-cooled Rhodamine 6G cations (R6G(+)) stored in a quadrupole ion trap at 90 K. The fluorescence resulting from excitation with continuous-wave 488 nm radiation was observed to disappear almost completely on a time scale of seconds, dependent in detail on the excitation laser fluence. Such decay can be explained by the accumulation of R6G(+) in a dark triplet state. This in turn facilitates the first lifetime determination of the lowest triplet state of free R6G(+) by direct ground-state recovery measurements. A lower bound for the half-life was found to be approximately 2 s. Adding oxygen in a volume fraction of 1% to the buffer gas leads to efficient quenching of the triplet state and correspondingly to complete suppression of the fluorescence intensity decay. Different rare gases were applied as buffers for collisional cooling, but no significant changes in the fluorescence properties were found.

We have investigated the gas phase triplet state lifetimes and dispersed fluorescence spectra of several types of rhodamine cations confined in a quadrupole ion trap and thermalized to 85 K. The measured triplet lifetimes of rhodamine cations Rh6G(+), Rh575(+), RhB(+), and Rh101(+) are found to be on the order of seconds, several orders of magnitude longer than those typically observed for the same dyes in optical condensed phase measurements. In addition dispersed fluorescence emission spectra in the gas phase at 85 K have been measured. The experimental gas phase results as well as solution measurements are compared to density functional calculations and the previous literature. Possible explanations for the discrepancy of gas and solution phase triplet lifetimes are discussed.

Electron loss and dissociation occur upon optical excitation of tetraanionic phthalocyanines trapped in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Experiments were carried out by irradiating at 355 nm and between 570 and 695 nm covering the Q band region of phthalocyanines. Laser fluence dependencies show a two-photon-process as the underlying absorption law for the observed decay which corresponds to an unexpectedly low kinetic shift given the 69-atom-size of this molecule and the activation energies expected for the decay channels. We assign this effect to the pronounced electronic metastability of these 4-fold negatively charged ions. Electronic excitation is associated not only with thermal ionization but also with a corresponding increase in the tunneling autodetachment rate.

In this work, we address the energetics of electron transfer in bridged diruthenium complexes from a theoretical and numerical perspective. The electronic structure of the bridged complexes is described by a tight-binding Hamiltonian, which is extended by an on-site spin pairing energy. The coupling of the system to a polarizable solvent is taken into account by a nonretarded reaction field. The resulting nonlinear Hamiltonian is solved within the Hartree–Fock mean-field approximation, and the emerging potential energy surface is analysed using Marcus´ theory of electron transfer reactions. For the systems studied here, the charge transfer rate depends on the chemical nature of the bridge rather than the intermetal distance. We discuss the special nature of the Creutz–Taube cation, which is on the border of charge delocalization.