In this contribution, we report on fast and ultrafast dynamics of a non-steroidal anti-inflammatory drug, piroxicam (PX), in methyl acetate (MAC) and triacetin (TAC), two solvents of different viscositi
es. The enol form of PX undergo
es a femtosecond (shorter than 100 fs) electronically excited state intramolecular proton-transfer reaction to produce keto tautomers. Th
ese structur
es exhibit an internal twisting motion to generate keto rotamers in
![](http://www.sciencedirect.com/scidirimg/entiti<font color=)
es/223c.gif" alt="not, vert, similar" title="not, vert, similar" border="0">2–5 ps, a time being longer in TAC. The transient absorption/emission spectrum is very broad indicating that the potential-energy surface at the electronically excited state is very flat, and reflecting the involvement of several coordinat
es along which the wavepacket of the fs-produced structur
es evolve.