Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

Abstract

Time-resolved photoelectron spectroscopy was used to obtain new information about the dynamics of electronic relaxation in gas-phase indole and 5-hydroxyindole following UV excitation with femtosecond laser pulses centred at 249 nm and 273 nm. Our analysis of the data was supported by ab initio calculations at the coupled cluster and complete-active-space self-consistent-field levels. The optically bright 1 L a and 1 L b electronic states of 1 ππ* character and spectroscopically dark and dissociative 1 πσ* states were all found to play a role in the overall relaxation process. In both molecules we conclude that the initially excited 1 L a state decays non-adiabatically on a sub 100 fs timescale via two competing pathways, populating either the subsequently long-lived 1 L b state or the 1 πσ* state localised along the N-H coordinate, which exhibits a lifetime on the order of 1 ps. In the case of 5-hydroxyindole, we conclude that the 1 πσ* state localised along the O-H coordinate plays little or no role in the relaxation dynamics at the two excitation wavelengths studied.

Investigation of electronically excited indole relaxation dynamics via photoionization and fragmentation pump-probe spectroscopy

“…This is highly corroborated by the author's theoretical investigations, 26 as well as the latter calculations of Sobolewski and Domcke. 9 This wavelength, however, is notably longer than the onset of the 1 πσ * channel previously reported by Ashfold and co-workers 41 as 263 nm, thus clarification of this discrepancy will require additional experimental work.…”

“…Further inconsistencies in time constants emerge between the work of Townsend and co-workers 26 and the timeresolved ion yield (TR-IY) investigations of Longarte and co-workers, 43 who report shorter relaxation times (∼400 fs) for deactivation on the 1 πσ * state at similar wavelengths. Although the experiments utilize disparate techniques, the results should, in principle, coincide with one another.…”

“…The most intense feature of their calculated spectrum is positioned at 5.84 eV, which is the same region the strongest absorption peak for indole presents itself, 26,[30][31][32] and is designated the 1 B b -state vertical excitation energy. The authors also calculate the 1 B a locale to be approximately 6.44 eV.…”

Revisiting the relaxation dynamics of isolated pyrrole

“…Recently our group, as part of an effort to unravel the relaxation pathways induced by the presence of πσ * character states in aromatic choromophres, [14][15][16][17][18][19][20][21] has employed the a) Author to whom correspondence should be addressed. Electronic mail: asier.longarte@ehu.es.…”

Time Resolved Photoelectron Spectroscopy of Thioflavin T Photoisomerization: A Simulation Study

“…TRPES has been proven to be an valuable technique for the analysis of the photophysics and photochemistry of molecules lie in their excited states. 18–20 Recent developments of photoelectron techniques in liquid phase had extended TRPES to solutions. 21–23 TRPES can reveal the details of the excited state isomerization and the fluorescence quenching mechanism of ThT.…”