Synchrotron excitation of DNA fluorescence. Decay time evidence for excimer emission at room temperature.

The first lifetime measurements of DNA fluorescence are reported. Natural and synthetic DNA have been excited by 1.76 ns pulses of synchrotron ultraviolet radiation (270 nm) and the time profile of the fluorescence has been measured by synchronous single-photon counting. A post-pulse exponentially decaying emission has been observed with a lifetime of 2.9 +/- 0.4 ns for calf thymus DNA and 3.0 +/- 0.3 ns for poly(dA-T); this is most likely an excimer fluorescence.