More Like this

1. Ab Initio Simulations of Poorly- and Well-Equilibrated (CH3CN)n¯ Cluster Anions: Assigning Experimental Photoelectron Peaks to Surface-Bound Electrons and Solvated Monomer and Dimer Anions

   https://doi.org/10.1021/acs.jpca.1c05855  

   Narvaez, W. A.; Schwartz, B. J. (January 2021, The journal of physical chemistry)

   Excess electrons in liquid acetonitrile are of particular interest because they exist in two different forms in equilibrium: they can be present as traditional solvated electrons in a cavity, and they can form some type of solvated molecular anion. Studies of small acetonitrile cluster anions in the gas phase show two isomers with distinct vertical detachment energies, and it is tempting to presume that the two gas-phase cluster anion isomers are precursors of the two excess electron species present in bulk solution. In this paper, we perform DFT-based ab initio molecular dynamics simulations of acetonitrile cluster anions to understand the electronic species that are present and why they have different binding energies. Using a long-range-corrected density functional that was optimally tuned to describe acetonitrile cluster anion structures, we have theoretically explored the chemistry of (CH3CN)n¯ cluster anions with sizes n=5,7 and 10. Since the temperature of the experimental cluster anions is not known, we performed two sets of simulations that investigated how the way in which the cluster anions are prepared affects the excess electron binding motif: one set of simulations simply attached excess electrons to neutral (CH3CN)n clusters, providing little opportunity for the clusters to relax in the presence of the excess electron, while the other set allowed the cluster anions to thermally equilibrate near room temperature. We find that both sets of simulations show three distinct electron binding motifs: electrons can attach to the surface of the cluster (dipole-bound) or be present as either solvated monomer anions, CH3CN¯, or as solvated molecular dimer anions, (CH3CN)2¯. All three species have higher binding energies at larger cluster sizes. Thermal equilibration strongly favors the formation of the valence-bound molecular anions relative to surface-bound excess electrons, and the dimer anion becomes more stable than the monomer anion and surface-bound species as the cluster size increases. The calculated photoelectron spectra from our simulations in which there was poor thermal equilibration are in good agreement with experiment, suggesting assignment of the two experimental cluster anion isomers as the surface-bound electron and the solvated molecular dimer anion. The simulations also suggest that the shoulder seen experimentally on the low-energy isomer's detachment peak is not part of a vibronic progression but instead results from molecular monomer anions. Nowhere in the size range that we explore do we see evidence for a non-valence, cavity-bound interior-solvated electron, indicating that this species is likely only accessible at larger sizes with good thermal equilibration. 

   more » « less
2. Enhancing the performance of a fused-ring electron acceptor via extending benzene to naphthalene

   https://doi.org/10.1039/c7tc04520d  

   Zhu, Jingshuai; Wu, Yang; Rech, Jeromy; Wang, Jiayu; Liu, Kuan; Li, Tengfei; Lin, Yuze; Ma, Wei; You, Wei; Zhan, Xiaowei (January 2018, Journal of Materials Chemistry C)

   We compared an indacenodithiophene(IDT)-based fused-ring electron acceptor IDIC1 with its counterpart IHIC1 in which the central benzene unit is replaced by a naphthalene unit, and investigated the effects of the benzene/naphthalene core on the optical and electronic properties as well as on the performance of organic solar cells (OSCs). Compared with benzene-cored IDIC1, naphthalene-cored IHIC1 shows a larger π-conjugation with stronger intermolecular π–π stacking. Relative to benzene-cored IDIC1, naphthalene-cored IHIC1 shows a higher lowest unoccupied molecular orbital energy level (IHIC1: −3.75 eV, IDIC1: −3.81 eV) and a higher electron mobility (IHIC1: 3.0 × 10 −4 cm 2 V −1 s −1 , IDIC1: 1.5 × 10 −4 cm 2 V −1 s −1 ). When paired with the polymer donor FTAZ that has matched energy levels and a complementary absorption spectrum, IHIC1-based OSCs show higher values of open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency relative to those of the IDIC1-based control devices. These results demonstrate that extending benzene in IDT to naphthalene is a promising approach to upshift energy levels, enhance electron mobility, and finally achieve higher efficiency in nonfullerene acceptor-based OSCs. 

   more » « less
3. Controlling Chemical Reactivity Under the Electron Microscope: Single‐Crystal‐to‐Single‐Crystal Splitting of Thymine Dimers Initiated by Electron Beam Ionization and Amplified by Electron Transfer‐Mediated Chain Reactions

   https://doi.org/10.1002/anie.2592959  

   Rai, Rishika; Konieczny, Krzysztof A; Garcia‐Garibay, Miguel A (July 2026, Angewandte Chemie International Edition)

   Three crystalline thymine dimers (TDs) obtained by solid state topochemical photodimerization were selected to explore radical ion-initiated solid-to-solid splitting reactions when exposed to the high energy beam of an electron microscope. While samples of cis-syn-thymine dimer (c,s-TD) were available from a previous study, samples of cis-syn-N,N-dimethyl-thymine dimer (c,s-TD-Me) and cis-anti-N,N-dimethyl-thymine dimer (c,a-TD-Me) were obtained by photoreaction of crystalline N,N-dimethyl-thymine (T-Me). The unexpected formation of c,a-TD-Me was rationalized on a topochemical basis based on a high-resolution X-ray structure of T-Me refined with DFT-calculated non-spherical scattering factors. When exposed to the electron beam (30-300 kV), recrystallized dimers underwent the expected splitting reaction back to T and T-Me as the only products. Electron beam-induced reactions studied as a function of electron fluence, beam energy, and temperature, confirmed an ionization-induced chain reaction propagated by a single electron transfer (SET) process with a chain length up to 80,000 product molecules per electron. Microcrystal electron diffraction (3D ED) analysis of the photodimers allowed for crystal structure determination with ca. 30% of in situ formed monomer. A long lived transient formed in single crystals of c,s-TD-Me was assigned by EPR as the TD-Me•+, in support of the suggested reaction mechanism. 

   more » « less
4. Exciton energy transfer reveals spectral signatures of excited states in clusters

   https://doi.org/10.1039/D0CP02042G  

   Lu, Wenchao; Metz, Ricardo B.; Troy, Tyler P.; Kostko, Oleg; Ahmed, Musahid (July 2020, Physical Chemistry Chemical Physics)

   Electronic excitation and concomitant energy transfer leading to Penning ionization in argon–acetylene clusters generated in a supersonic expansion are investigated with synchrotron-based photoionization mass spectrometry and electronic structure calculations. Spectral features in the photoionization efficiency of the mixed argon–acetylene clusters reveal a blue shift from the 2 P 1/2 and 2 P 3/2 excited states of atomic argon. Analysis of this feature suggests that excited states of argon clusters transfer energy to acetylene, resulting in its ionization and successive evaporation of argon. Theoretically calculated Ar n ( n = 2–6) cluster spectra are in excellent agreement with experimental observations, and provide insight into the structure and ionization dynamics of the clusters. A comparison between argon–acetylene and argon–water clusters reveals that argon solvates water better, allowing for higher-order excitons and Rydberg states to be populated. These results are explained by theoretical calculations of respective binding energies and structures. 

   more » « less
5. Real-time capture of nuclear motions influencing photoinduced electron transfer

   https://doi.org/10.1039/d4sc01876a  

   Kim, Pyosang; Roy, Subhangi; Valentine, Andrew; Liu, Xiaolin; Kromer, Sarah; Kim, Tae Wu; Li, Xiaosong; Castellano, Felix N; Chen, Lin X (September 2024, Chemical Science)

   Although vibronic coupling phenomena have been recognized in the excited state dynamics of transition metal complexes, their impact on photoinduced electron transfer (PET) remains largely unexplored. This study investigates coherent wavepacket (CWP) dynamics during PET processes in a covalently linked electron donor–acceptor complex featuring a cyclometalated Pt(II) dimer as the donor and naphthalene diimide (NDI) as the acceptors. Upon photoexciting the Pt(II) dimer electron donor, ultrafast broadband transient absorption spectroscopy revealed direct modulation of NDI radical anion formation through certain CWP motions and correlated temporal evolutions of the amplitudes for these CWPs with the NDI radical anion formation. These results provide clear evidence that the CWP motions are the vibronic coherences coupled to the PET reaction coordinates. Normal mode analysis identified that the CWP motions originate from vibrational modes associated with the dihedral angles and bond lengths between the planes of the cyclometalating ligand and the NDI, the key modes altering their p-interaction, consequently influencing PET dynamics. The findings highlight the pivotal role of vibrations in shaping the favorable trajectories for the efficient PET processes. 

   more » « less