Pump probe transient absorption

Recently, the interactions of 2AP singlet excited states with other DNA bases have been studied by pump-probe transient absorption spectroscopy with a time resolution of -600 fs [38]. In the 2AP sequences containing either of the four natural bases (A, C, G, and T), or inosine (I) ... 

Ethylene glycol is a very viscous liquid and the molecule presents two close OH groups. It has to be noticed that, among all the different solvents studied by pulse radiolysis, the transition energy of the solvated electron absorption band is maximum in liquid ethylene glycol. For these reasons, the electron in EG seems to have a special behaviour and it is of great interest to study the dynamics of the formation of equilibrated solvated electron. Within this context, the present communication deals with the dynamics of solvation in EG of electrons produced by photoionisation of the solvent at 263 nm. The formation of solvated electrons is followed by pump-probe transient absorption spectroscopy in the visible spectral range from 425 to 725 nm and also in near IR. For the first time, the absorption spectrum of the precursor of the equilibrated electron is observed in EG. Our results are shortly compared by those obtained in water and methanol. 

We have made a sub-picosecond pump-probe transient absorption study on Phenol Blue at 308 K in trifluoromethane near the gas-liquid critical density and at the high density (about twice of the critical density) where small amount of 2,2,2-trifluoroethanol is added as cosolvent. The ground state hole created by the pump pulse is mostly broadened by about 1 ps, and we could not detect any meaningful density effect on this process. 

Figure 11.2 Typical set-ups for tuneable femtosecond pump/probe transient absorption spectrometers in...

Fig. 12 Experimental setup for femtosecond (pump probe) transient absorption spectroscopy.

The dynamics of the photochemical process involving the ZnTPPS-ZnTMPyP ion pair has been recently investigated by pump-probe transient absorption. The transient absorption responses shown in Figure 11.10 were obtained by pumping the porphyrins at 560 nm and probing at 510 nm. It should be indicated that the depopulation of the Si state for ZnTPPS and ZnTMPyP in their monomeric form exhibits time constants of 1.6 and 0.6 ns, respectively. As mentioned before, this relaxation mainly contains contribution from radiative... 

Femtosecond Pump Probe Transient Absorption Microscopy (PPTAM)... 

Figure 7.9 Block diagram of the femtosecond pump-probe transient absorption microscope.

The most daunting barrier to reaching higher time resolution in fluorescence microscopy is not of a technical nature, it is rather imposed by the photon bottleneck discussed above. The probability that an excellent fluorophore such as rhodamine 6G, will spontaneously emit a photon within a 10 fs window is smaller than 1 x 10 leading to a dauntingly large number of necessary excitations. Pump probe transient absorption microscopy (PPTAM) is not limited by the radiative rate and with carefully optimized all-reflective imaging components should be able to reach 20 fs or better time resolution. 

Figure 10.2 Principle of pump-probe transient absorption spectroscopy.

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