Ultrafast intersystem crossing in 9,10-anthraquinones and intramolecular charge separation in an anthraquinone-based dyad.
Femtosecond transient absorption spectroscopy was employed to determine quantitatively the ultrafast S1-T1 intersystem crossing in a 2-substituted 9,10-anthraquinone derivative (3), kisc = 2.5 x 10(12) s-1. Notwithstanding this rapid process, photoexcitation of dyad 1 is followed by competition between intersystem crossing and intramolecular charge separation, the latter leading to a short-lived (2 ps) singlet charge-transfer (CT) state. The local triplet state itself undergoes slower charge separation to populate a relatively long-lived (130 ns) triplet CT state. An earlier report about the formation of an extremely long-lived CT state (> 900 micros) in 1 was found to be erroneous and was related to the sacrificial photo-oxidation of the dimethylsulfoxide solvent used in that study. Finally, some important criteria have been formulated for future experimental validation of "unusually long-lived" CT states.
Ramesdonk
Hendrik J van
HJ
Chemistry Department, HIMS, University of Amsterdam, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands.
Bakker
Bartholomeus H
BH
Groeneveld
Michiel M
MM
Verhoeven
Jan W
JW
Allen
Ben D
BD
Rostron
James P
JP
Harriman
Anthony
A