Visible and Ultraviolet Spectroscopy of Gas Phase Rhodamine 575 Cations

Abstract

The visible and ultraviolet spectroscopy of gas phase rhodamine 575 cations has been studied experimentally by action-spectroscopy in a modified linear ion trap between 220 and 590 nm and by time-dependent density functional theory (TDDFT) calculations. Three bands are observed that can be assigned to the electronic transitions S₀ → S₁, S₀ → S₃, and S₀ → (S₈,S₉) according to the theoretical prediction. While the agreement between theory and experiment is excellent for the S₃ and S₈/S₉ transitions, a large shift in the value of the calculated S₁ transition energy is observed. A theoretical analysis of thermochromism, potential vibronic effects, and–qualitatively–electron correlation revealed it is mainly the latter that is responsible for the failure of TDDFT to accurately reproduce the S₁ transition energy, and that a significant thermochromic shift is also present. Finally, we investigated the nature of the excited states by analyzing the excitations and discussed their different fragmentation behavior. We hypothesize that different contributions of local versus charge transfer excitations are responsible for 1-photon versus 2-photon fragmentation observed experimentally