Ultrafast Pump-Repump-Probe Photochemical Hole Burning as a Probe of Excited-State Reaction Pathway Branching.
Joshua A SnyderArthur E BraggPublished in: The journal of physical chemistry letters (2018)
We demonstrate pump-repump-probe (PRP) transient hole burning as a spectroscopic tool for differentiating reactive from nonreactive deactivation of excited photochemical reactants observed by transient absorption spectroscopy (TAS). This method utilizes a time-delayed, wavelength-tunable ultrafast pulse to alter the excited reactant population, with the impact of "repumping" quantified through depletions in photoproduct absorption. We apply this approach to characterize dynamics affecting the nonadiabatic photocyclization efficiency to form S0 dihydrotriphenylene (DHT) following 266 nm excitation of ortho-terphenyl (OTP). TAS studies revealed bimodal deactivation of OTP*, but neither relaxation time scale (700 fs and 3.0 ps) could be assigned unambiguously to DHT formation due to overlap of excited-state and product spectra. PRP studies reveal that S1 OTP only cyclizes on the slower of these time scales, with the faster process attributable to nonreactive deactivation. We demonstrate that this method offers greater photochemical insights without assuming models to globally fit spectral transients collected by TAS.
Keyphrases
- energy transfer
- quantum dots
- living cells
- electron transfer
- single molecule
- platelet rich plasma
- cerebral ischemia
- case control
- single cell
- blood pressure
- molecular dynamics
- high resolution
- fluorescent probe
- perovskite solar cells
- molecular docking
- optical coherence tomography
- solar cells
- photodynamic therapy
- subarachnoid hemorrhage
- magnetic resonance imaging
- density functional theory
- brain injury
- magnetic resonance
- blood brain barrier
- dna methylation
- contrast enhanced
- mass spectrometry
- solid state