Hannover 2020 – scientific programme

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MO: Fachverband Molekülphysik

MO 10: Collisions and Reactions

MO 10.6: Talk

Wednesday, March 11, 2020, 12:15–12:30, f142

Consecutive photoinduced electron transfer: The mechanism of the photocatalyst rhodamine-6G. — •Fabian Brandl, Sebastian Bergwinkl, Carina Allacher, and Bernhard Dick — Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany.

The dye Rhodamine-6G (R6G) acts as photocatalyst via photoinduced electron transfer by forming the R6G radical (reduction potential ca. -0.90 V) after excitation with green light. König et al. proposed a strategy, termed consecutive photoinduced electron transfer (conPET), that adds the energy of two photons for a photoreduction, using a photogenerated radical as an intermediate [1]. Subseqently it has been reported that photoexcitation of the R6G radical at 420 nm splits aryl bromides, suggesting a conPET process [2]. Here we present a study of the mechanism of the formation and photoreactions of the R6G radical by using transient spectroscopy (femtoseconds to minutes) and quantum chemical calculations. We conclude that one photon of 540 nm light produces two R6G radicals. The photoexcited radical decays in ca. 350 fs, either relaxing to the ground state or releasing an electron to the solvent, which returns on a timescale of nanoseconds. Unless the substrate is already attached to the radical, it is reduced by solvated electrons. Vibrational cooling of hot R6G and hot R6G radical occurs within 10ps.

[1] B. König et al. Science. 2014, 346, 725-728.

[2] B. König et al. Chem Commun. 2016, 52, 8695-8698.