Delocalization Of Wave Functions Research Articles

Chiral Steric Effect for Improved Phase Transition and Exciton Dynamics in Efficient and Stable All‐Polymer Solar Cells

AbstractChiral materials exhibit distinctive properties that improve the performance of organic solar cells (OSCs). In this study, chiral PM6 is integrated into PM6:PY‐IT blends to fabricate chiral quasi‐binary OSCs (cOSCs). The produced devices displayed an increased short‐circuit current and fill factor, achieving a peak efficiency of 16.60% compared to 15.96% for the standard PM6:PY‐IT cell. Additionally, the incorporation of chiral PM6 significantly enhanced the thermal stability, with the cOSCs retaining over 80% of their initial efficiency after 1000 h of operation. The steric effect of chiral PM6 altered the molecular packing, thereby improving the overall crystallinity. The optimized nanoscale domain morphology resulted in a more effective blend film, leading to superior device performance. Moreover, the chirality‐induced orbital angular momentum increased the ratio of triplet states, which is a key factor for increasing the photocurrent in OSCs. The delocalization of electron wavefunctions is driven by chiral steric effects, and it diminished the Coulomb attraction between the interfacial electron–hole pairs, which enhanced the efficient charge generation. This study provides valuable insights into the role of chirality in optimizing both the performance and stability of OSCs.

Nuclear Quantum Effects Enhance Structural Stability but Accelerate Charge Carrier Recombination in MHyPbBr3 Perovskite.

Hybrid organic-inorganic perovskites exhibit significant nuclear quantum effects (NQEs) due to their light hydrogen atoms. By performing ring polymer molecular dynamics, ab initio molecular dynamics, and nonadiabatic molecular dynamics simulations on the MHyPbBr3 (MHy+ = CH3NH2NH2+) perovskites, we demonstrate that NQEs stabilize the lattice by suppressing atomic motions and accelerate nonradiative charge recombination. This stabilization arises from the synergistic effects of the Pb-N coordination bonds and N-H···Br hydrogen bonds, which enhance organic-inorganic interactions. As a result, Pb-Br octahedra, particularly [Pb(1)Br6]4- octahedra supporting electron and hole, are well-preserved, promoting electronic wavefunction delocalization and increasing electron-hole overlap. These effects enhance nonadiabatic coupling by overcoming the reduced atomic motions. Overall, this and the prolonged decoherence time accelerate the nonradiative electron-hole recombination due to NQEs. Our study highlights the unique influence of NQEs on the geometrical stability and charge carrier dynamics in MHyPbBr3, offering fundamental insights for future material design.

An explicitly correlated potential energy surface for N2-OCS complex: Out-of-plane motion and tunneling dynamics.

A four-dimensional potential energy surface (4D-PES) has been constructed for the N2-OCS complex. The PES is achieved by applying the explicitly correlated coupled cluster method, which incorporates single, double, and perturbative triple excitations [CCSD(T)-F12a], along with the augmented correlation consistent triple zeta (aug-cc-pVTZ) basis set. The rovibrational levels are precisely determined and assigned through bound state calculations and wavefunction analysis. The calculated transition frequencies reproduce the experimental observations accurately, achieving an RMSE of 0.0005cm-1 for the 23 rotational transitions (J ≤ 6, Ka ≤ 2). The R-φ contour plot of the wave function clearly demonstrates the unambiguous delocalization of the dihedral angle, and the averaged geometry of the ground vibrational state is determined to be non-planar with φ = 90°. To obtain a quantitative analysis of this phenomenon, we expanded the 3H-solution model [Guo et al., J. Quant. Spectrosc. Radiat. Transfer 309 (2023) 108711] from a three-dimensional system (Ar-AgF) to a nine-dimensional system (N2-OCS). Based on this model, the tunneling splitting was calculated to be 0.0822cm-1, which excellently matches the experimental result of 0.0817cm-1. The excellent agreement between the theoretical and experimental results suggests that the wavefunction delocalization and out-of-plane motion can be attributed to the tunneling effects in the ground vibrational state.

Improving Three-Photon Fluorescence of Near-Infrared Quantum Dots for Deep Brain Imaging by Suppressing Biexciton Decay.

Three-photon fluorescence microscopy (3PFM) is a promising brain research tool with submicrometer spatial resolution and high imaging depth. However, only limited materials have been developed for 3PFM owing to the rigorous requirement of the three-photon fluorescence (3PF) process. Herein, under the guidance of a band gap engineering strategy, CdTe/CdSe/ZnS quantum dots (QDs) emitting in the near-infrared window are designed for constructing 3PF probes. The formation of type II structure significantly increased the three-photon absorption cross section of QDs and caused the delocalization of electron-hole wave functions. The time-resolved transient absorption spectroscopy confirmed that the decay of biexcitons was significantly suppressed due to the appropriate band gap alignment, which further enhanced the 3PF efficiency of QDs. By utilizing QD-based 3PF probes, high-resolution 3PFM imaging of cerebral vasculature was realized excited by a 1600 nm femtosecond laser, indicating the possibility of deep brain imaging with these 3PF probes.

Vibrational Coupling Infrared Nanocrystallography.

Coupling between molecular vibrations leads to collective vibrational states with spectral features sensitive to local molecular order. This provides spectroscopic access to the low-frequency intermolecular energy landscape. In its nanospectroscopic implementation, this technique of vibrational coupling nanocrystallography (VCNC) offers information on molecular disorder and domain formation with nanometer spatial resolution. However, deriving local molecular order relies on prior knowledge of the transition dipole magnitude and crystal structure of the underlying ordered phase. Here we develop a quantitative model for VCNC by relating nano-FTIR collective vibrational spectra to the molecular crystal structure from X-ray crystallography. We experimentally validate our approach at the example of a metal organic porphyrin complex with a carbonyl ligand as the probe vibration. This framework establishes VCNC as a powerful tool for measuring low-energy molecular interactions, wave function delocalization, nanoscale disorder, and domain formation in a wide range of molecular systems.

Spin relaxation of electron and hole polarons in ambipolar conjugated polymers

The charge-transport properties of conjugated polymers have been studied extensively for opto-electronic device applications. Some polymer semiconductors not only support the ambipolar transport of electrons and holes, but do so with comparable carrier mobilities. This opens the possibility of gaining deeper insight into the charge-transport physics of these complex materials via comparison between electron and hole dynamics while keeping other factors, such as polymer microstructure, equal. Here, we use field-induced electron spin resonance spectroscopy to compare the spin relaxation behavior of electron and hole polarons in three ambipolar conjugated polymers. Our experiments show unique relaxation regimes as a function of temperature for electrons and holes, whereby at lower temperatures electrons relax slower than holes, but at higher temperatures, in the so-called spin-shuttling regime, the trend is reversed. On the basis of theoretical simulations, we attribute this to differences in the delocalization of electron and hole wavefunctions and show that spin relaxation in the spin shuttling regimes provides a sensitive probe of the intimate coupling between charge and structural dynamics.

Hyperbolic exciton polaritons in a van der Waals magnet

Exciton polaritons are quasiparticles of photons coupled strongly to bound electron-hole pairs, manifesting as an anti-crossing light dispersion near an exciton resonance. Highly anisotropic semiconductors with opposite-signed permittivities along different crystal axes are predicted to host exotic modes inside the anti-crossing called hyperbolic exciton polaritons (HEPs), which confine light subdiffractionally with enhanced density of states. Here, we show observational evidence of steady-state HEPs in the van der Waals magnet chromium sulfide bromide (CrSBr) using a cryogenic near-infrared near-field microscope. At low temperatures, in the magnetically-ordered state, anisotropic exciton resonances sharpen, driving the permittivity negative along one crystal axis and enabling HEP propagation. We characterize HEP momentum and losses in CrSBr, also demonstrating coupling to excitonic sidebands and enhancement by magnetic order: which boosts exciton spectral weight via wavefunction delocalization. Our findings open new pathways to nanoscale manipulation of excitons and light, including routes to magnetic, nonlocal, and quantum polaritonics.

Hybrid Metal-Ligand Interfacial Dipole Engineering of Functional Plasmonic Nanostructures for Extraordinary Responses of Optoelectronic Properties.

Programmable manipulation of inorganic-organic interfacial electronic properties of ligand-functionalized plasmonic nanoparticles (NPs) is the key parameter dictating their applications such as catalysis, photovoltaics, and biosensing. Here we report the localized surface plasmon resonance (LSPR) properties of gold triangular nanoprisms (Au TNPs) in solid state that are functionalized with dipolar, conjugated ligands. A library of thiocinnamate ligands with varying surface dipole moments were used to functionalize TNPs, which results in ∼150 nm reversible tunability of LSPR peak wavelength with significant peak broadening (∼230 meV). The highly adjustable chemical system of thiocinnamate ligands is capable of shifting the Au work function down to 2.4 eV versus vacuum, i.e., ∼2.9 eV lower than a clean Au (111) surface, and this work function can be modulated up to 3.3 eV, the largest value reported to date through the formation of organothiolate SAMs on Au. Interestingly, the magnitude of plasmonic responses and work function modulation is NP shape dependent. By combining first-principles calculations and experiments, we have established the mechanism of direct wave function delocalization of electrons residing near the Fermi level into hybrid electronic states that are mostly dictated by the inorganic-organic interfacial dipole moments. We determine that both interfacial dipole and hybrid electronic states, and vinyl conjugation together are the key to achieving such extraordinary changes in the optoelectronic properties of ligand-functionalized, plasmonic NPs. The present study provides a quantitative relationship describing how specifically constructed organic ligands can be used to control the interfacial properties of NPs and thus the plasmonic and electronic responses of these functional plasmonics for a wide range of plasmon-driven applications.

Synthesis, spectroscopic, crystallographic, quantum and molecular docking investigations of cis-4,5-diphenylimidazolidine-2-thione

Synthesis, spectroscopic, crystallographic, quantum and molecular docking investigations of cis-4,5-diphenylimidazolidine-2-thione

Impact of organic–inorganic wavefunction delocalization on the electronic and optical properties of one-dimensional hybrid perovskites

This work investigates the impact of electronic couplings between the organic and inorganic components of one-dimensional hybrid perovskites on their ground-state and excited-state electronic properties and optical properties.

Stark-localization as a probe of nanostructure geometry

It is a central tenet of quantum mechanics that spatial resolution is limited by the wave nature of particles. Energies of stationary states reflect delocalized wave functions and cannot be ascribed to any single point. Yet, electrons confined in nanostructures become localized against the boundary by strong electric fields. Energies then reflect the local curvature of the nanostructure surface rather than entire volume. We propose using spectroscopy of Stark-localized states to map nanostructure surface curvature. By varying field direction, local curvatures are extracted from absorption spectra. Moreover, the required field strength is shown to be feasible experimentally. We use nanowires with elliptic cross section as a detailed benchmark providing quantitative error estimates and practical guide lines.

Attosecond Photoionization Dynamics: from Molecules over Clusters to the Liquid Phase

Photoionization is a process taking place on attosecond time scales. How its properties evolve from isolated particles to the condensed phase is an open question of both fundamental and practical relevance. Here, we review recent work that has advanced the study of photoionization dynamics from atoms to molecules, clusters and the liquid phase. The first measurements of molecular photoionization delays have revealed the attosecond dynamics of electron emission from a molecular shape resonance and their sensitivity to the molecular potential. Using electron-ion coincidence spectroscopy these measurements have been extended from isolated molecules to clusters. A continuous increase of the delays with the water-cluster size has been observed up to a size of 4-5 molecules, followed by a saturation towards larger clusters. Comparison with calculations has revealed a correlation of the time delay with the spatial extension of the created electron hole. Using cylindrical liquid-microjet techniques, these measurements have also been extended to liquid water, revealing a delay relative to isolated water molecules that was very similar to the largest water clusters studied. Detailed modeling based on Monte-Carlo simulations confirmed that these delays are dominated by the contributions of the first two solvation shells, which agrees with the results of the cluster measurements. These combined results open the perspective of experimentally characterizing the delocalization of electronic wave functions in complex systems and studying their evolution on attosecond time scales.

Direct d−d hybridization mechanism for strong anisotropic carrier transport in layered Mo2SBr2

Transition metal sulfide halides such as ${\mathrm{Mo}}_{2}{\mathrm{SBr}}_{2}$ have exhibited excellent anisotropy in their electronic and optical properties. To explore the mechanism behind this strong anisotropic behavior, we performed first-principles calculations on the anisotropic mechanical, optical, and electronic properties of monolayer ${\mathrm{Mo}}_{2}{\mathrm{SBr}}_{2}$. We find that monolayer ${\mathrm{Mo}}_{2}{\mathrm{SBr}}_{2}$ demonstrates obvious anisotropy in its electron mobility, ${\ensuremath{\mu}}_{e}$, with an extremely high ${\ensuremath{\mu}}_{e}$ of $10,356.08\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{--1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{--1}$ along the $b$ direction. We attributed this strong anisotropy in monolayer ${\mathrm{Mo}}_{2}{\mathrm{SBr}}_{2}$ to the unique characters in the orbital coupling. Our further studies show that direct $d\text{\ensuremath{-}}d$ coupling between the nearest-neighboring Mo atoms plays a critical role in the unique carrier transport properties and strong anisotropy. Direct $d\text{\ensuremath{-}}d$ coupling provides a fast hole transport channel along the $c$ direction. Furthermore, wavefunction delocalization at the valence band maximum is significantly enhanced by this $d\text{\ensuremath{-}}d$ hybridization, which further reduces the effective mass of holes. Our work provides physical insights into the origin of strong anisotropy in the photoelectric properties of transition metal sulfide halides. Transition metal sulfide halides are demonstrated to have great potential applications in novel nanoelectronic devices.

CARNOT: a Fragment-Based Direct Molecular Dynamics and Virtual-Reality Simulation Package for Reactive Systems.

Traditionally, the study of reaction mechanisms of complex reaction systems such as combustion has been performed on an individual basis by optimizations of transition structure and minimum energy path or by reaction dynamics trajectory calculations for one elementary reaction at a time. It is effective, but time-consuming, whereas important and unexpected processes could have been missed. In this article, we present a direct molecular dynamics (DMD) approach and a virtual-reality simulation program, CARNOT, in which plausible chemical reactions are simulated simultaneously at finite temperature and pressure conditions. A key concept of the present ab initio molecular dynamics method is to partition a large, chemically reactive system into molecular fragments that can be adjusted on the fly of a DMD simulation. The theory represents an extension of the explicit polarization method to reactive events, called ReX-Pol. We propose a highest-and-lowest adapted-spin approximation to define the local spins of individual fragments, rather than treating the entire system by a delocalized wave function. Consequently, the present ab initio DMD can be applied to reactive systems consisting of an arbitrarily varying number of closed and open-shell fragments such as free radicals, zwitterions, and separate ions found in combustion and other reactions. A graph-data structure algorithm was incorporated in CARNOT for the analysis of reaction networks, suitable for reaction mechanism reduction. Employing the PW91 density functional theory and the 6-31+G(d) basis set, the capabilities of the CARNOT program were illustrated by a combustion reaction, consisting of 28 650 atoms, and by reaction network analysis that revealed a range of mechanistic and dynamical events. The method may be useful for applications to other types of complex reactions.

Electrical control of orbital and vibrational interlayer coupling in bi- and trilayer 2H−MoS2

Manipulating electronic interlayer coupling in layered van der Waals (vdW) materials is essential for designing opto-electronic devices. Here, we control vibrational and electronic interlayer coupling in bi- and trilayer 2H-MoS$_2$ using large external electric fields in a micro-capacitor device. The electric field lifts Raman selection rules and activates phonon modes in excellent agreement with ab-initio calculations. Through polarization resolved photoluminescence spectroscopy in the same device, we observe a strongly tunable valley dichroism with maximum circular polarization degree of $\sim 60\%$ in bilayer and $\sim 35\%$ in trilayer MoS$_2$ that are fully consistent with a rate equation model which includes input from electronic band structure calculations. We identify the highly delocalized electron wave function between the layers close to the high symmetry $Q$ points as the origin of the tunable circular dichroism. Our results demonstrate the possibility of electric field tunable interlayer coupling for controlling emergent spin-valley physics and hybridization driven effects in vdW materials and their heterostructures.

Systemic consequences of disorder in magnetically self-organized topological MnBi2Te4/(Bi2Te3) n superlattices

MnBi2Te4/(Bi2Te3) n materials system has recently generated strong interest as a natural platform for the realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic (FM) MnBi2Te4/(Bi2Te3) n it is found that migration of Mn between MnBi2Te4 septuple layers (SLs) and otherwise non-magnetic Bi2Te3 quintuple layers (QLs) has systemic consequences—it induces FM coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional theory studies show that Mn disorder within an SL causes delocalization of electron wave functions and a change of the surface band structure as compared to the ideal MnBi2Te4/(Bi2Te3) n . These findings highlight the critical importance of inter- and intra-SL disorder towards achieving new QAH platforms as well as exploring novel axion physics in intrinsic topological magnets.

Switching Behavior of a Heterostructure Based on Periodically Doped Graphene Nanoribbon

We theoretically propose a switching device that operates at room temperature. The device is an in-plane heterostructure based on a periodically boron-doped (nitrogen-doped) armchair graphene nanoribbon, which has been experimentally fabricated recently. The calculated $I$-$V$ curve shows that for a realistic device with interface width longer than $20$ nm, nonzero electric current occurs only in the region of bias voltage between $\ensuremath{-}0.22$ and $0.28$ V, which is beneficial to low-voltage operation. Furthermore, in this case, the electric current is robust against the change of the potential profile in the interface since the metallic impurity-induced sub-bands with delocalized wave functions contribute to the transmission exclusively. This also suggests the high response speed of the proposed device. We also discuss the temperature dependence, the output impedance, the effect of phonons, and the possible regimes to extend our work, which suggest that our model may have potential room-temperature nanoelectronics applications.

2D Vibrational Exciton Nanoimaging of Domain Formation in Self-Assembled Monolayers.

Order, disorder, and domains affect many of the functional properties in self-assembled monolayers (SAMs). However, carrier transport, wettability, and chemical reactivity are often associated with collective effects, where conventional imaging techniques have limited sensitivity to the underlying intermolecular coupling. Here we demonstrate vibrational excitons as a molecular ruler of intermolecular wave function delocalization and nanodomain size in SAMs. In the model system of a 4-nitrothiophenol (4-NTP) SAM on gold, we resolve coupling-induced peak shifts of the nitro symmetric stretch mode with full spatio-spectral infrared scattering scanning near-field optical microscopy. From modeling of the underlying 2D Hamiltonian, we infer domain sizes and their distribution ranging from 3 to 12 nm across a field of view on the micrometer scale. This approach of vibrational exciton nanoimaging is generally applicable to study structural phases and domains in SAMs and other molecular interfaces.

Single-chain polymerization dynamics and conformational mechanics of conjugated polymers

<h2>Summary</h2> Conjugated polymers possess unique optoelectrical properties. Characterizing their synthesis and mechanical processability is crucial for tailored applications. Their poor solubility presents a universal challenge, however. Here, we report a single-molecule study, which circumvents the solubility challenge, of the polymerization kinetics and conformational mechanics of polyacetylene, a prototypical conjugated polymer. We monitor the growth of individual long-chain polyacetylenes during ring-opening metathesis polymerization of cyclooctatetraene. We discover that polyacetylene forms nonequilibrium conformational entanglements, whose kinetic instability and structural looseness appear to render its polymerization more facile than that of polycyclooctene, a nonconjugated analog. This relative kinetics is contrary to monomer reactivity predictions. Moreover, even under identical solvent conditions, individual polyacetylenes show diverse extension-versus-force scaling behaviors; many span multiple scaling regimes predicted previously but never observed. The extracted persistence and Kuhn length of polyacetylene are also significantly shorter than its wavefunction delocalization length, indicating that polyacetylene can maintain backbone conjugation while staying flexible.

Photoluminescence Blinking and Biexciton Auger Recombination in Single Colloidal Quantum Dots with Sharp and Smooth Core/Shell Interfaces.

There is an inconsistence on whether a smooth core/shell interface can reduce Auger recombination and suppress photoluminescence (PL) blinking in single colloidal quantum dots (QDs). Here, we investigate the influence of a core/shell interface on PL blinking and biexciton Auger recombination by comparing the single-dot PL spectra of CdxZn1-xSeyS1-y/ZnS core/shell QDs with sharp and smooth interfaces. The inconsistence can be clarified when considering different PL blinking mechanisms. For the single QDs showing Auger blinking, a smooth core/shell interface potential can suppress PL blinking through reducing the Auger recombination. In contrast, we find slightly reduced biexciton Auger recombination rates but increased PL blinking activities in the band-edge carrier (BC)-blinking QDs with the smooth core/shell interface. This is because the smooth interface potential cannot reduce the PL blinking caused by the transfer of electrons to the surface states; however, there is potential to increase electron wave function delocalization for reducing the biexciton Auger recombination rate.