Ultrafast Photoionization Dynamics of Indole in Water

Abstract

Indole in aqueous solution is photoionized near threshold following single photon absorption from a femtosecond laser pulse at 260 nm. Transient absorption measurements are performed using a white-light continuum probe pulse. Excited state absorption of neutral indole molecules is characterized accurately in 1-propanol where photoexcitation at 260 nm does not lead to photoionization. The presence of 0.75 M carbon tetrachloride in a solution of indole/1-propanol leads to the formation of indole radical cations on a picosecond time scale. While solvated electrons are formed in aqueous indole within our time resolution of 200 fs, measurements of the transient absorbance out to 100 ps are flat and indicate that geminate recombination is insignificant on this time scale. This result contrasts sharply with the geminate recombination dynamics observed following the photoionization of neat water. This indicates that the bimolecular reaction between indole radical cations and solvated electrons is considerably slower than the diffusion limit. We suggest that geminate recombination arising from solute photoionization in polar solvents may be slower than previously thought.

Ultrafast dynamics of photochromic compound based on oxazine ring opening

“…3) surprisingly well reproduces the S 1 → S n absorption of indole radical cation (Indolyl) in aqueous environment that has been observed by various spectroscopic methods [28][29][30]. Although indolyl radical and 3H-indolium cation investigated here are not exactly the same molecules, the sizes and structures of their conjugated systems are similar, thus presumably leading to a close match between the excited state absorption (ESA) spectra.…”

Photodynamics of potent antioxidants: ferulic and caffeic acids

“…3d (caffeic acid)) display broad absorptions in the red, akin to that of the ubiquitous solvated electron. 40 The absorption feature in the blue-end of the spectrum also matches closely to the phenolic radical absorption, which has been proposed to be formed through dissociation via a tunnelling mechanism, along the O-H coordinate of the phenolic moiety, following one-photon absorption. [33][34][35]41 However these absorptions show a quadratic dependence upon pump fluence in the power dependence measurements (see ESI †).…”

Comparing molecular photofragmentation dynamics in the gas and liquid phases

“…The adiabatic ionisation energy of a solute molecule is reduced in the presence of a polar solvent, enabling autoionisation at energies well below the (gas phase) ionisation potential. [19][20][21][22] Recombination processes are even more common. Such processes are essentially nonexistent in the gas phase (except at very high pressures) but are clearly pertinent to any discussion of photodissociation in the condensed phase.…”

“…Comparing the static UV/Visible absorption spectra of p-MePhSMe in cyclohexane and in CH 3 CN (see ESI †), we note that the S 1 -S 0 absorption in the former is slightly red-shifted. The slow (ns) timescale for dissociation from the S 1 ; v = 0 level (t Diss(v=0) = 1.4(1) ns in cyclohexane, 560 (20) ps in CD 3 CN) reflects its reliance on the very poor overlap between the extremities of the S 1 ; v = 0 and S 2 continuum wavefunctions; any small shift in the relative positions of these two PESs would have a profound effect on the efficiency of non-adiabatic coupling via CI1 and thus on the rate of S-Me bond scission. Thus the sensitivity of k Diss to change in solvent is not particularly surprising.…”