Pump‐Probe Fragmentation Action Spectroscopy: A Powerful Tool to Unravel Light‐Induced Processes in Molecular Photocatalysts

Abstract

We present ap roof of concept that ultrafast dynamics combined with photochemical stability information of molecular photocatalysts can be acquired by electrospray ionization mass spectrometry combined with time-resolved femtosecond laser spectroscopyi na nion trap.T his pumpprobe "fragmentation action spectroscopy" gives straightforward access to information that usually requires high purity compounds and great experimental efforts.R esults of gasphase studies on the electronic dynamics of two supramolecular photocatalysts compare well to previous findings in solution and give further evidence for ad irected electron transfer,akey process for photocatalytic hydrogen generation.

Theoretical Investigation of the Electron‐Transfer Dynamics and Photodegradation Pathways in a Hydrogen‐Evolving Ruthenium–Palladium Photocatalyst

“…This contribution focuses on the supramolecular photocatalyst [(tbbpy) 2 Ru(tpphz)PdCl 2 ] 2 + (tbbpy = 4,4'-di-tert-butyl-2,2'bipyridine, tpphz = tetrapyrido[3,2-a:2',3'-c:3''''-h:2''',3'''-j]phenazine) ( Figure 1), whichw ill be denoted as RuPdCl 2 .T his systemw as introduced in 2006b yR au et al [8] and has since then be the subject of manye xperimental and computational studies [9][10][11][12][13][14][15] to understandi ts photophysical properties and photocatalytic activity.S everal relateds ystemsw ere subsequently synthesized in order to improve the stability of the photocatalysta nd to optimize the catalytic turnover. [14,[16][17][18][19] To realizel ight-driven hydrogen production,t he catalytic site must undergod ouble photoreduction.…”

Time‐Resolved Spectroscopy and Electronic Structure of Mono‐and Dinuclear Pyridyl‐Triazole/DPEPhos‐Based Cu(I) Complexes

“…An important prerequisite for obtaining transients by this method, however, is that the interrogation by the probe pulse should lead to different fragmentation efficiencies (or different fragment species) for the primary electronically excited state in comparison to the subsequently reached states, which are produced by (electronic) relaxation processes, for example IC or ISC. [ 35b , 36 ] Characteristic transients of the three species for a maximum time delay of 180 ps are displayed in Figure 6 , kinetic fit results are given in Table 2 . Additionally, transients for different maximum time delays are presented in Figures SI‐14–SI‐21.…”

“…The experimental setup for photodissociative action spectroscopy was described elsewhere in detail. [ 35b , 59 ] Shortly, a femto‐ or nanosecond, respectively, UV‐pump ( λ pump : 350–370 nm, 0.3 μJ) beam is focused ( f =50 cm) and quasi‐collinearly combined with a femtosecond NIR‐probe ( λ probe : 1200 nm, 130 μJ) beam in a Paul‐type ion trap (∼1 mm diameter) through fused silica window (3 mm thickness) of the modified mass spectrometer. For static photodissociation spectra only the pump beam (femto‐ or nanosecond pulses, respectively) is used and manually scanned in 3–5 nm steps in the range of 240–400 nm with a constant pulse energy (2 μJ) controlled by neutral density filters and an irradiation time of 100 ms, so that each ion packet was irradiated with ∼100 UV pulses followed by mass spectrometric analysis.…”

“…UV pump-NIR probe τ-PD spectroscopy [35] was conducted on the isolated ionic complexes [CuLH] + , [Cu 2 L'H] + and [Cu 2 L'H 2 ] 2 + (PF 6 ) À in an ion trap mass spectrometer (with time delays up to 800 ps and the pump wavelength set to 350 nm), whereas the probe wavelength was fixed at 1200 nm for multiphoton excitation and fragmentation. An important prerequisite for obtaining transients by this method, however, is that the interrogation by the probe pulse should lead to different fragmentation efficiencies (or different fragment species) for the primary electronically excited state in comparison to the subsequently reached states, which are produced by (electronic) relaxation processes, for example IC or ISC.…”

Achieving high molecular alignment and orientation for CH$$_3$$F through manipulation of rotational states with varying optical and THz laser pulse parameters

“…Molecular alignment and orientation (A&O) is essential in the fields of ultrafast science, molecular imaging, time-dependent spectroscopy and detailed interrogation of molecular dynamics 1 . Laser-induced field-free or sudden molecular alignment of gas-phase molecules can result in a highly peaked angular distribution of the rotational wavepacket 2 , and it plays an important role in improving the output signal quality of studies that are sensitive to the angle between the molecule and the direction of polarization of the laser field 3 , 4 , such as high harmonic generation 5 , 6 , strong field ionization 7 , laser-induced reactions 8 , time-dependent spectroscopy 9 , attosecond pulse shaping 10 , and molecular orbital tomography 11 . Many theoretical and experimental efforts 12 – 14 are reported towards understanding and controlling the non-adiabatic and adiabatic A&O dynamics of molecules with different symmetry.…”