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Published August 25, 2005 | public
Journal Article

Ultrafast unequilibrated charge transfer: A new channel in the quenching of fluorescent biological probes


The dynamics of two biological fluorescent probes, 2-aminopurine (Ap) and daunomycin, were studied using both femtosecond transient absorption and fluorescence upconversion techniques. Various Ap-containing structures were investigated in solution: free Ap, non-covalently bonded (with guanine, adenine, and tryptophan) and covalently bonded in DNA constructs (with guanine, 7-deazaguanine, and adenine). The distinct difference of transient absorption and fluorescence dynamics on the ultrafast time scale, and their dependence on free energy change (ΔG), and the abrupt decrease of the initial fluorescence intensity suggest the efficient depopulation by charge transfer from the unequilibrated hot molecules. We provide a model for this possibly general mechanism and obtain the rate constants for charge separation, vibrational relaxation, and charge recombination.

Additional Information

© 2005 Elsevier B.V. Received 8 June 2005; in final form 20 June 2005. Available online 19 July 2005. This work was supported by a grant from the National Science Foundation. We thank Dr. Spencer Baskin for his critical comments.

Additional details

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October 20, 2023