DNA Intercalated Psoralen Undergoes Efficient Photoinduced
Electron Transfer
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Abstract
The interaction of psoralens with
DNA has been used for therapeutic
and research purposes for decades. Still the photoinduced behavior
of psoralens in DNA has never been observed directly. Femtosecond
transient absorption spectroscopy is used here to gain direct insight
into the photophysics of a DNA-intercalated psoralen (4′-aminomethyl-4,5′,8-trimethyl-psoralen
(AMT)). Intercalation reduces the excited singlet lifetime of AMT
to 4 ps compared with 1400 ps for AMT in water. This singlet quenching
prohibits the population of the triplet state that is accessed in
free AMT. Instead, a DNA to AMT electron transfer takes place. The
resulting radical pair decays primarily via charge recombination with
a time constant of 30 ps. The efficient electron transfer observed
here reveals a completely new aspect of the psoralen–DNA interaction