Observation of reversible conformational interconversion accompanied by 3p internal conversions in Rydberg-excited N,N-dimethylethylamine.

Conformational dynamics has been well observed in the 3s Rydberg state of amines, whereas its observation in higher-energy, non-equilibrium 3p Rydberg states is very rare, especially for a reversible conformational transition that could compete with other non-adiabatic transitions. Herein, we report the observation of a reversible conformational interconversion phenomenon in the 3p Rydberg excited-state dynamics of N,N-dimethylethylamine (DMEA). Upon electronic excitation, a forward and backward interconversion between the initially prepared 3p_l and 3p_h conformers accompanied by 3p internal conversions occurs, resulting in a 3p_l/3p_h equilibrium ratio of 61 %/39 % within ∼1.

UV wavelength-dependent photoionization quantum yields for the dark nπ* state of aqueous thymidine.

Despite the important role of the dark nπ* state in the photostability of thymidine in aqueous solution, no detailed ultraviolet (UV) wavelength-dependent investigation of the nπ* quantum yield (QY) in aqueous thymidine has been experimentally performed. Here, we investigate the wavelength-dependent photoemission spectra of aqueous thymidine from 266.7 to 240 nm using liquid-microjet photoelectron spectroscopy.

Ultrafast conformation-dependent charge transfer in N, N, N', N'-tetramethyl-1,3-propanediamine: Effect of flexible carbon skeleton on electron lone pair interactions.

Flexible three-carbon skeleton makes N, N, N', N'-tetramethyl-1,3-propanediamine (TMPDA) an important diamine system to investigate the conformation-dependent electron lone pair interactions and charge delocalization. The charge transfer process linked to structural motions of the three-carbon skeleton has been monitored in real time by the Rydberg electron binding energy (BE) spectra of TMPDA coupled with quantum chemical calculations. Optical excitation to the 3p state with a 200 nm pump pulse initially generated a localized charge on one of the two nitrogen atoms that may partially transfer to the other one.

Structural dynamics upon photoinduced charge transfer in N,N,N',N'-tetramethylmethylenediamine.

The ultrafast structural motion linked to the charge transfer process in Rydberg excited N,N,N',N'-tetramethylmethylenediamine (TMMDA) has been monitored in real time using femtosecond time-resolved photoelectron imaging coupled with quantum chemical calculations. Optical excitation to the 3 s Rydberg state initially populates the charge on one of the two amine groups, resulting in a charge-localized structure in the Franck-Condon (FC) region. As the wavepacket evolves on the 3 s potential surface, the molecular geometry changes with time, leading to the corresponding variation in the charge distribution.

Non-adiabatic dynamics of Rydberg-excited diethylamine.

Femtosecond time-resolved photoelectron spectroscopy was employed to investigate the ultrafast non-adiabatic dynamics of diethylamine (DEA). Following the direct excitations of the two main conformational structures (i.e.

Liquid-microjet photoelectron imaging spectrometry for liquid aqueous solutions.

A new liquid-microjet photoelectron imaging (PEI) spectrometer has been constructed that combines the liquid-microjet technique with velocity-map imaging. This novel method enables us to simultaneously measure the energy and angular distributions of the photoelectrons produced from highly volatile liquid solutions. The capability of the spectrometer has been demonstrated by recording the photoelectron image of the aqueous 2-furfural.

Identification of a bridge-specific intramolecular exciton dissociation pathway in donor-π-acceptor alternating conjugated polymers.

Intramolecular exciton dissociation is critical for high efficient mobile charge carrier generations in organic solar cells. Yet despite much attention, the effects of π bridges on exciton dissociation dynamics in donor-π-acceptor (D-π-A) alternating conjugated polymers remain still unclear. Here, using a combination of femtosecond time-resolved transient absorption (TA) spectroscopy and steady-state spectroscopy, we track ultrafast intramolecular exciton relaxation dynamics in three D-π-A alternating conjugated polymers which were synthesized by Qin's group and named HSD-A, HSD-B, HSD-C.

Femtosecond time-resolved observation of butterfly vibration in electronically excited o-fluorophenol.

The butterfly vibration during the hydrogen tunneling process in electronically excited o-fluorophenol has been visualized in real time by femtosecond time-resolved ion yield spectroscopy coupled with time-resolved photoelectron imaging technique. A coherent superposition of out-of-plane C-F butterfly motions is prepared in the first excited electronic state (S). As the C-F bond vibrates with respect to the aromatic ring, the nuclear geometry varies periodically, leading to the corresponding variation in the photoionization channel.

Real-time visualization of the vibrational wavepacket dynamics in electronically excited pyrimidine via femtosecond time-resolved photoelectron imaging.

The vibrational wavepacket dynamics at the very early stages of the S-T intersystem crossing in photoexcited pyrimidine is visualized in real time by femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. A coherent superposition of the vibrational states is prepared by the femtosecond pump pulse at 315.3 nm, resulting in a vibrational wavepacket.

Superexcited State Dynamics of OCS: An Experimental Identification of Three Competing Decay Channels among Autoionization, Internal Conversion, and Neutral Predissociation.

The 7sσ and 6pσ superexcited Rydberg states of OCS belonging to series converging onto the B̃Σ ionic limit have been successfully prepared by three-photon UV excitation, and their ensuing competing relaxation processes have been probed by a time-delayed IR ionization pulse. The time profiles of S ions, which encode their fragmentation mechanism, are only observable at high pump intensities, thus providing unique experimental identification of the neutral predissociation channel producing S* atoms. Benefiting from this feature and by comparison with the time behavior of OCS ions, three competing relaxation channels are identified: autoionization associated with both X̃Π and ÃΠ ionic states; internal conversion to isoenergetic R states, the deactivation of which manifests as a picosecond decay in the time profile of OCS ions; picosecond neutral predissociation appearing as a nondecaying plateau in the time profiles of S ions.

Real-time observation of cascaded electronic relaxation processes in p-Fluorotoluene.

Ultrafast electronic relaxation processes following two photoexcitation of 400nm in p-Fluorotoluene (pFT) have been investigated utilizing time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Cascaded electronic relaxation processes started from the electronically excited S state are directly imaged in real time and well characterized by two distinct time constants of ~85±10fs and 2.4±0.

Study of ultrafast dynamics of 2-picoline by time-resolved photoelectron imaging.

The dynamics of electronically excited states in 2-picoline is studied using femtosecond time-resolved photoelectron imaging spectroscopy. The internal conversion from the S(2) state to the vibrationally excited S(1) state is observed in real time. The secondarily populated high vibronic S(1) state deactivates further to the S(0) state.

Real-time visualization of the dynamic evolution of CS2 4d and 6s Rydberg wave packet components.

The dynamic evolution of CS2 4d and 6s Rydberg wave packet components has been experimentally visualized via femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. The temporal evolution of the four components of the prepared Rydberg wave packet is directly observed as time-dependent changes of the intensities of different parts in the main photoelectron peak. Furthermore, time-resolved photoelectron angular distributions (PADs) clearly reflect the different component characters of 4d and 6s molecular orbitals.