Laser flash photolysis of 7-(piperazin-1-yl) fluoroquinolones leads to the formation of a triplet excited state ((3)A*) at the end of the pulse (lambda(max) 520, 610, and 620 nm for enoxacin, ciprofloxacin, and norfloxacin, respectively). Phosphate and bicarbonate buffers react with (3)A* to form a secondary triplet (B-3*, reaction rates (0.8-9.9) x 10(8) M-1 s(-1)), whose T-T absorption is red-shifted (Am, 670 nm for enoxacin, 700 nm for ciprofloxacin and norfloxacin). The formation of a secondary triplet is not a common process and disagrees with previous work suggesting that electron transfer occurs between phosphate buffer and the primary triplet excited state with the formation of the anion radical of the fluoroquinolone (FQ(center dot-)). We have shown that the FQ(center dot-) transient absorption spectrum is quite distinct from that of B-3*. The photophysical characteristics of B-3* have been determined by energy transfer to naproxen, and it has been found that its energy is lower than that of (3)A*.