FEMTOSECOND HOLE-BURNING SPECTROSCOPY OF THE DYE DCM IN SOLUTION - THE TRANSITION FROM THE LOCALLY EXCITED TO A CHARGE-TRANSFER STATE

Transient spectra of the styryl dye DCM thylene-2-methyl-6-p-dimethyla minostyryl-4H-pyran) in methanol were studied by the pump-supercontinu um probe technique with 40 fs time resolution. A theory of measurement s with a supercontinuum probe is presented, Gain and absorption spectr a were measured from 400 to 800 nm with 1.5 nm resolution. Before 70 f s, prominent spectral structure is observed which is mainly due to res onant Raman processes. At longer times the spectrum undergoes a red sh ift and change of shape (time constant 140 fs) with a well-defined iso sbestic point. After 300 fs solvation becomes apparent, The early tran sient spectrum is assigned to the locally excited state of DCM.