Interfacial Dipole Engineering for Energy Level Alignment in NiOx-Based Quantum Dot Light-Emitting Diodes.

The solution-derived non-stoichiometric nickel oxide (NiOx) is a promising hole-injecting material for stable quantum dot light-emitting diodes (QLEDs). However, the carrier imbalance due to the misalignment of energy levels between the NiOx and polymeric hole-transporting layers (HTLs) curtails the device efficiency. In this study, the modification of the NiOx surface is investigated using either 3-cyanobenzoic acid (3-CN-BA) or 4-cyanobenzoic acid (4-CN-BA) in the QLED fabrication. Morphological and electrical analyses revealed that both 4-CN-BA and 3-CN-BA can enhance the work function of NiOx, reduce the oxygen vacancies on the NiOx surface, and facilitate a uniform morphology for subsequent HTL layers. Moreover, it is found that the binding configurations of dipole molecules as a function of the substitution position of the tail group significantly impact the work function of underlying layers. When integrated in QLEDs, the modification layers resulted in a significant improvement in the electroluminescent efficiency due to the enhancement of energy level alignment and charge balance within the devices. Specifically, QLEDs incorporating 4-CN-BA achieved a champion external quantum efficiency (EQE) of 20.34%, which is a 1.8X improvement in comparison with that of the devices utilizing unmodified NiOx (7.28%). Moreover, QLEDs with 4-CN-BA and 3-CN-BA modifications exhibited prolonged operational lifetimes, indicating potential for practical applications.

Polar Covalent Triazine Frameworks as High-Performance Potassium Metal Battery Cathodes.

The exploration of potassium metal batteries (PMBs) has been intensified, leveraging potassium's abundant availability, low redox potential, and small Stokes radius. Covalent triazine frameworks (CTFs) stand out for their accessible nitrogen sites and customizable structures, making them attractive electrode materials. Nonetheless, there is a lack of established design principles to guide the development of high-performance PMBs using CTFs. In this work, CTFs consisting of different monomers are used as PMB cathodes to investigate the structure-performance correlation. The electronic structure analysis reveals the polar characteristic of a CTF derived from the tetracyanoquinodimethane monomer, setting it apart with superior capacity (161 mAh g-1 at 0.1 A g-1), rate performance (85 mAh g-1 at 5 A g-1), and stability (capacity retention of 81% after 1000 cycles) over three non-polar counterparts in PMBs. Calculations based on density functional theory support the exceptional performance with increased K+ adsorption energy. Ultimately, among multifaceted factors, the polarity of CTF is the leading element that determines the K+ storage capability. These findings pave the way for the development of prudent CTF electrodes for high-performance PMBs.

Dual Function of Naphthalenediimide Supramolecular Photocatalyst with Giant Internal Electric Field for Efficient Hydrogen and Oxygen Evolution.

Organic supramolecular photocatalysts have garnered widespread attention due to their adjustable structure and exceptional photocatalytic activity. Herein, a novel bis-dicarboxyphenyl-substituent naphthalenediimide self-assembly supramolecular photocatalyst (SA-NDI-BCOOH) with efficient dual-functional photocatalytic performance is successfully constructed. The large molecular dipole moment and short-range ordered stacking structure of SA-NDI-BCOOH synergistically create a giant internal electric field (IEF), resulting in a remarkable 6.7-fold increase in its charge separation efficiency. Additionally, the tetracarboxylic structure of SA-NDI-BCOOH greatly enhances its hydrophilicity. Thus, SA-NDI-BCOOH demonstrates efficient dual-functional activity for photocatalytic hydrogen and oxygen evolution, with rates of 372.8 and 3.8 µmol h-1, respectively. Meanwhile, a notable apparent quantum efficiency of 10.86% at 400 nm for hydrogen evolution is achieved, prominently surpassing many reported supramolecular photocatalysts. More importantly, with the help of dual co-catalysts, it exhibits photocatalytic overall water splitting activity with H2 and O2 evolution rates of 3.2 and 1.6 µmol h-1. Briefly, this work sheds light on enhancing the IEF by controlling the molecular polarity and stacking structure to dramatically improve the photocatalytic performance of supramolecular materials.

Analysis of the Unusual Chemical Bonds and Dipole Moments of AeF- (Ae=Be-Ba): A Lesson in Covalent Bonding.

Quantum chemical calculations of the anions AeF- (Ae=Be-Ba) have been carried out using ab initio methods at the CCSD(T)/def2-TZVPP level and density functional theory employing BP86 with various basis sets. The detailed bonding analyses using different charge- and energy partitioning methods show that the molecules possess three distinctively different dative bonds in the lighter species with Ae=Be, Mg and four dative bonds when Ae=Ca, Sr, Ba. The occupied 2p atomic orbitals (AOs) and to a lesser degree the occupied 2s AO of F- donate electronic charge into the vacant spx(σ) and p(π) orbitals of Be and Mg which leads to a triple bond Ae F-. The heavier Ae atoms Ca, Sr, Ba use their vacant (n-1)d AOs as acceptor orbitals which enables them to form a second σ donor bond with F- that leads to quadruply bonded Ae F- (Ae=Ca-Ba). The presentation of molecular orbitals or charge distribution using only one isodensity value may give misleading information about the overall nature of the orbital or charge distribution. Better insights are given by contour line diagrams. The ELF calculations provide monosynaptic and disynaptic basins of AeF- which nicely agree with the analysis of the occupied molecular orbitals and with the charge density difference maps. A particular feature of the covalent bonds in AeF- concerns the inductive interaction of F- with the soft valence electrons in the (n)s valence orbitals of Ae. The polarization of the (n)s2 electrons induces a (n)spx hybridized lone-pair orbital at atom Ae, which yields a large dipole moment with the negative end at Ae. The concomitant formation of a vacant (n)spx AO of atom Ae, which overlaps with the occupied 2p(σ) AO of F-, leads to a strong covalent σ bond.

Homogeneous Dephasing in Photosynthetic Bacterial Reaction Centers: Time Correlation Function Approach.

A new tractable linear electronic transition dipole moment time correlation function (ETDMTCF) that accurately accounts for electronic dephasing, asymmetry, and width of 1-phonon profile, which the zero-phonon line (ZPL) contributes to it, in Rhodopseudomonas viridis bacterial reaction center is derived. This time correlation function proves to be superior to other frequency-domain expressions in case of strong electron-phonon coupling (which is often the case in bacterial RCs and pigment-protein complexes), many vibrational modes involved, and high temperature, whereby more vibronic and electronic (sequence) transitions would arise. The Fourier transform of this ETDMTCF leads to asymmetric multiphonon profiles composed of Lorentzian distribution and Gaussian distribution on the high- and low-energy sides, respectively, whereby the overtone widths fold themselves with that of the one-phonon profile. This ETDMTCF also features expedient computation in large systems using asymmetric phonon profiles to account correctly for dephasing and pigment-protein interaction (electron-phonon coupling). The derived ETDMTCF allows computing all nonlinear optical signals in both time and frequency domains, through the nonlinear dipole moment time correlation functions (as guided by nonlinear optical response theory) in line with the eight Liouville space pathways. The linear transition dipole moment time correlation function is of a central value as the nonlinear transition dipole moment time correlation function is expressed in terms of the linear transition dipole moment time correlation function, derived herein. One of the great advantages of presenting this ETDMTCF is its applicability to nonlinear transition dipole moment time correlation functions in line with the eight Liouville space pathways needed in computing nonlinear signals. As such, there is more to the utility and applicability of the presented ETDMTCF besides computational expediency and efficiency. Results show good agreement with the reported literature. The intimate connection between a one-phonon profile and the corresponding bath spectral density in photosynthetic complexes is discussed.

Synthesis, Solvatochromism and Estimation of Ground and Excited State Dipole Moments of Silylated Benzothiazole Dyes.

Dyes derived from benzothiazoles are an important class of heterocycles which have remarkable photophysical properties. New photoluminescent 2-phenylbenzothiazole derivatives containing different functional groups were synthesized in high yields and used for silylated derivatives synthesis. The new photoactive compounds were fully characterized and their photophysical properties were investigated. The absorption and fluorescence spectra of the benzothiazoles and their silylated derivatives were evaluated in a series of organic solvents. The results showed that the benzothiazoles present absorption in the ultraviolet range and emission in the blue region with moderate quantum yields and large Stokes shift. The solvatochromism of these compounds was investigated by using Lippert and ET(30) Dimroth-Reichardt empirical solvent polarity scales. The dipole moments obtained by Bakshiev and Kawaski-Chamma-Viallet equations revealed that the excited states were more polar than the ground states.

Photophysical Investigation of One Pot Synthesized Novel Indenofluorene Derivative (BDP) as a Fluorescent Chemosensor for the Detection of Fe3+ Ion.

An Indane-1-one derivative 11-(1-benzyl-1H-indol-3-yl)-10,12-dihydrodiindeno[1,2-b:2',1'-e]-pyridine (BDP) has been synthesized by the reaction of Indan-1-one with 1-benzyl-1H-indole-3-carbaldehyde. FT-IR, 1H-NMR, 13N-NMR and Mass spectroscopic techniques has been used to confirmed the structure of BDP. The observed photophysical changes in BDP across various solvents were associated. The impact of various interactions on photophysical parameters, including Stokes shift, dipole moment, oscillator strength, and fluorescence quantum yields, has been assessed in relation to solvent polarity. Moreover, BDP demonstrates potential as a selective fluorescent chemosensor for detecting Fe3+ ion within a range of cations in an aqueous DMSO environment. A thorough investigation into the recognition mechanism of BDP towards Fe3+ ion has been conducted using Benesi-Hildebrand and Stern-Volmer, measurements. BDP forms a 2:1 complex with the Fe3+ ion, exhibiting fluorescent quenching behaviour.

Estimation of Electric Dipole Moment by Solvatochromism, Computational Method, and Study of the Effect of Solvents by Preferential Solvation of 6 - Methoxy-4-(4-Nitro-Phenoxy Methyl)-Chromen-2-One (6mnpm).

At room temperature, the absorption and fluorescence properties of coumarin 6-Methoxy-4-(4-nitro-phenoxy methyl)-chromen-2-one (6MNPM) are investigated in pure organic solvents and a combination of acetonitrile (ACN) and tetrahydrofuran (THF). The pure solvents' influence on spectral characteristics is examined by applying theories such as Kamlet and Catalan's multiple linear regression techniques, Reichardt's microscopic solvent polarity parameter, and the Lippert-Mataga polarity function. The significant role of solute-solvent interactions in pure solvents, particularly dielectric interaction and hydrogen bonding. However, hydrogen bonding interactions dominate the contribution of dielectric interactions. The electric dipole moments of both the ground as well as excited states had been calculated using the Solvatochromic method. The value of the excited state electric dipole moment and the redshifts of the emission spectra show that the emitting singlet state has an intramolecular charge transfer (ICT) character. From Catalan's linear regression, we found that di-polarity has a much smaller influence than polarizability. By solvation study, we conclude that Tetrahydrofuran solvent is preferred over Acetonitrile.

Nonlinear Optical Refraction and Absorption Features of Methyl Orange Dye in Polar Solvents.

Herein, we report the nonlinear optical (NLO) refraction and absorption features of azo dye namely, methyl orange (MO) dissolved in ethanol, methanol, acetone, 1-propanol, DMF and DMSO. The UV-Visible absorption study reveals that the maximum absorption spectrum of MO dye appeared towards longer wavelength by increasing the solvent polarizability is the result of red shift or bathochromic shift. The Z-scan method is utilized to measure the third-order NLO features of MO dye in different polar solvents. A continuous wave laser with 5-mW power and an excitation wavelength of 405 nm is employed in the Z-scan technique. The NLO features including nonlinear index of refraction (n2), nonlinear coefficient of absorption (ß) and third-order NLO susceptibility (χ3) are calculated to be the order of 10-7 cm2/W, 10-2 cm/W and 10-7 esu, respectively. The NLO index of refraction shows peak-valley transmittance is the result of self-defocusing and NLO absorption coefficient exhibits both positive and negative nonlinearity owing to saturable absorption (SA) and reverse saturable absorption (RSA). The effect of solvent polarizability and dipole moment on third-order NLO susceptibility of MO dye is discussed. Based on the experimental results, an azo dye MO appears to be a promising option for NLO applications in the future.

Synthesis, Spectral Characterization and Photoluminescence of 3-chloro-6-methoxy-2-(methylsulfanyl)quinoxaline in Different Solvents: An Experimental and Theoretical Investigation Using DFT.

In the present work, we synthesized 3-chloro-6-methoxy-2-(methyl sulfanyl) quinoxaline (3MSQ) using a microwave-assisted synthesis method. The physicochemical structural analysis of the synthesized compound utilizing 1H-NMR, 13C-NMR, and FT-IR spectroscopy techniques. The photophysical properties of 3MSQ was examined through absorption and fluorescence spectroscopy. Spectroscopic analyses revealed a bathochromic shift in both absorption and fluorescence spectra, attributed to the π → π* transition. Ground and excited state dipole moments was experimentally determined using the solvatochromic shift method, employing various correlations such as Lippert's, Bakhshiev's, Kawski-Chamma-Viallet's equations, and solvent polarity parameters. Our findings indicate that the excited state dipole moments exceed those of the ground state, suggesting increased polarity in the excited state. Further, the while detailed bond length, bond angles, dihedral angles, Mulliken charge distribution, ground state dipole moments and HOMO-LUMO energy gap estimated through ab initio computations using Gaussian-09W. The value of energy band gap obtained from both the methods are in good agreement. Furthermore, employing DFT computational analysis, we identified reactive centers such as electrophilic and nucleophilic sites using molecular electrostatic potential (MESP) 3D plots. Additionally, CIE chromaticity analysis was performed to understand the photoluminescent properties of 3MSQ. The insights derived from these analyses contribute to a better understanding of the molecule's electronic structure, photophysical properties, and solute-solvent interactions, thus providing valuable information regarding its behaviour and characteristics under diverse conditions. These results contribute to a comprehensive understanding of the molecular structure and properties of 3-chloro-6-methoxy-2-(methyl sulfanyl) quinoxaline (3MSQ).

Separating Charge Centers of Chain Segments in Dielectric Elastomer through Steric Hindrance Engineering.

Theoretically, separating the positive and negative charge centers of the chain segments of dielectric elastomers (DEs) is a viable alternative to the conventional decoration of chain backbone with polar handles, since it can dramatically increase the dipole vector and hence the dielectric constant (ε') of the DEs while circumvent the undesired impact of the decorated polar handles on the dielectric loss (tan δ). Herein, a novel and universal method is demonstrated to achieve effective separation of the charge centers of chain segments in homogeneous DEs by steric hindrance engineering, i.e., by incorporating a series of different included angle-containing building blocks into the networks. Both experimental and simulation results have shown that the introduction of these building blocks can create a spatially fixed included angle between two adjacent chain segments, thus separating the charge center of the associated region. Accordingly, incorporating a minimal amount of these building blocks (≈5 mol%) can lead to a considerably sharp increase (≈50%) in the ε' of the DEs while maintaining an extremely low tan δ (≈0.006@1 kHz), indicating that this methodology can substantially optimize the dielectric performance of DEs based on a completely different mechanism from the established methods.

Experimental perspectives on the matter-antimatter asymmetry puzzle: developments in electron EDM and [Formula: see text] experiments.

In the search for clues to the matter-antimatter puzzle, experiments with atoms or molecules play a particular role. These systems allow measurements with very high precision, as demonstrated by the unprecedented limits down to [Formula: see text] e cm on electron EDM using molecular ions, and relative measurements at the level of [Formula: see text] in spectroscopy of antihydrogen atoms. Building on these impressive measurements, new experimental directions offer potential for drastic improvements. We review here some of the new perspectives in those fields and their associated prospects for new physics searches. This article is part of the theme issue 'The particle-gravity frontier'.

Intensity of the Earth's magnetic field: Evidence for a Mid-Paleozoic dipole low.

The Mesozoic Dipole Low (MDL) is a period, covering at least ∼80 My, of low dipole moment that ended at the start of the Cretaceous Normal Superchron. Recent studies of Devonian age Siberian localities identified similarly low field values a few tens of million years prior to the Permo-Carboniferous Reverse Superchron (PCRS). To constrain the length and timing of this potential dipole low, this study presents paleointensity estimates from Strathmore (∼411 to 416 Ma) and Kinghorn (∼332 Ma) lava flows, United Kingdom. Both localities have been studied for paleomagnetic poles (Q values of 6 to 7), and the sites were assessed for their suitability for paleointensity from paleodirections, rock magnetic analysis, and microscopy. Thermal and microwave experiments were used to determine site mean paleointensity estimates of ∼3 to 51 µT (6 to 98 ZAm2) and 4 to 11 µT (9 to 27 ZAm2) from the Strathmore and Kinghorn localities, respectively. These, and all the sites from 200 to 500 Ma from the (updated) Paleointensity database (PINT15), were assessed using the Qualitative Paleointensity criteria (QPI). The procurement of reliable (QPI ≥ 5) weak paleointensity estimates from this and other studies indicates a period of low dipole moment (median field strength of 17 ZAm2) from 332 to 416 Ma. This "Mid-Paleozoic Dipole Low (MPDL)" bears a number of similarities to the MDL, including the substantial increase in field strength near the onset of the PCRS. The MPDL also adds support to the inverse relationship between reversal frequency and field strength and a possible ∼200-My cycle in paleomagnetic behavior relating to mantle convection.

Discovery of internal rotation and conformers of 1,2-dichloroethane: the dawn of the concept of conformation.

In 1932, Mizushima and Higasi reported the dependence of the dipole moments of 1,2-dichloroethane on both temperature and solvent in the Proceedings of the Imperial Academy, Japan. This report was followed by their first proposal of the existence of conformers that exchanged by internal rotation about a C-C single bond based on experimental data. Their monumental work marked the beginning of the essential concept of conformation in modern stereochemistry. Their proposal was later confirmed by the direct observation of the anti and gauche conformers of 1,2-dichloroethane by Raman spectroscopy, and further supported by other experimental and theoretical methods. The relative stabilities of the anti and gauche conformers of 1,2-dichloroethane and other 1,2-disubstituted ethanes were discussed in terms of steric, electrostatic, and stereoelectronic effects based on analysis of calculated data. Those studies influenced the development of subsequent research in organic chemistry, such as the conformational analysis of cyclohexane derivatives and the isolation of chiral gauche conformers.

Enhancing the Performance of MoS2 Field-Effect Transistors Using Self-Assembled Monolayers: A Promising Strategy to Alleviate Dielectric Layer Scattering and Improve Device Performance.

Field-effect transistors (FETs) based on two-dimensional molybdenum disulfide (2D-MoS2) have great potential in electronic and optoelectronic applications, but the performances of these devices still face challenges such as scattering at the contact interface, which results in reduced mobility. In this work, we fabricated high-performance MoS2-FETs by inserting self-assembling monolayers (SAMs) between MoS2 and a SiO2 dielectric layer. The interface properties of MoS2/SiO2 were studied after the inductions of three different SAM structures including (perfluorophenyl)methyl phosphonic acid (PFPA), (4-aminobutyl) phosphonic acid (ABPA), and octadecylphosphonic acid (ODPA). The SiO2/ABPA/MoS2-FET exhibited significantly improved performances with the highest mobility of 528.7 cm2 V-1 s-1, which is 7.5 times that of SiO2/MoS2-FET, and an on/off ratio of ~106. Additionally, we investigated the effects of SAM molecular dipole vectors on device performances using density functional theory (DFT). Moreover, the first-principle calculations showed that ABPA SAMs reduced the frequencies of acoustic and optical phonons in the SiO2 dielectric layer, thereby suppressing the phonon scattering to the MoS2 channel and further improving the device's performance. This work provided a strategy for high-performance MoS2-FET fabrication by improving interface properties.

Comparative Study of Two Spectral Methods for Estimating the Excited State Dipole Moment of Non-Fluorescent Molecules.

The electronic absorption spectral characteristics of cycloimmonium ylids with a zwitterionic structure have been analyzed in forty-three solvents with different hydrogen bonding abilities. The two ylids lack fluorescence emission but are very dynamic in electronic absorption spectra. Using the maximum of the ICT band, the goal was to establish an accurate relationship between the shift of the ICT visible band and the solvent parameters and to estimate two of the descriptors of the first (the) excited state: the dipole moment and the polarizability. Two procedures were involved: the variational method and the relationships of the Abe model. The results indicate that the excited state dipole moment of the two methylids decreases in the absorption process in comparison with the ground state. The introduction of a correction term in the Abe model that neglects the intermolecular H-bonding interactions leads to a more accurate determination of the two descriptors. The strong solvatochromic response of both ylids has been further applied in distinguishing the solvents as a function of their specific parameters. Principal component analysis was applied to five selected properties, including the maximum of the charge transfer band. The results were further applied to discriminate several binary solvent mixtures.

Deep-Ultraviolet Transparent Mixed Metal Sulfamates with Enhanced Nonlinear Optical Properties and Birefringence.

Enhancing anisotropy through the controlled arrangement of anionic groups is essential for improving the nonlinear optical (NLO) performance of non-π-conjugated NLO materials. In this study, we present the successful synthesis of the first examples of mixed alkali metal-alkaline earth metal sulfamate materials, including noncentrosymmetric Cs2 Mg(NH2 SO3 )4 ⋅ 4H2 O (1), as well as centrosymmetric K2 Ca(NH2 SO3 )4 (2) and Rb2 Ca(NH2 SO3 )4 (3). All three compounds feature promising deep ultraviolet cut-off edges, notably 1 with a cut-off edge below 180 nm. The synergy of Cs+ and Mg2+ cations in 1 facilitated the successful alignment of polar [NH2 SO3 ] tetrahedra in a uniform orientation. Remarkably, 1 stands as the sole instance among reported sulfamate compounds with a co-parallel anionic arrangement, yielding a very large dipole moment compared to other non-π-conjugated NLO materials. Moreover, the substantial dipole moment of 1 yields an enhanced second harmonic generation response, approximately 2.3 times that of KH2 PO4 , and a large birefringence of 0.054 at 546.1 nm. The approach of regulating the arrangement of anionic groups using aliovalent cations holds promise for advancing the exploration of non-π-conjugated NLO materials.

Exploring Macroscopic Dipoles of Designed Cyclic Peptide Ordered Assemblies to Harvest Piezoelectric Properties.

Crystalline materials exhibiting non-centrosymmetry and possessing substantial surface dipole moments play a critical role in piezoelectricity. Designing biocompatible self-assembled materials with these attributes is particularly challenging when compared to inorganic materials and ceramics. In this study, we elucidate the crystal conformations of novel cyclic peptides that exhibit self-assembly into tubular structures characterized by unidirectional hydrogen bonding and piezoelectric properties. Unlike cyclic peptides derived from alternating L- and D-amino acids, those derived from new δ-amino acids demonstrate the formation of self-assembled tubes with unidirectional hydrogen bonds. Further, the tightly packed tubular assemblies and higher macrodipole moments result in superior piezoelectric coefficients compared to peptides with lower macrodipole moments. Our findings underscore the potential for designing cyclic peptides with unidirectional hydrogen bonds, thereby paving the way for their application in design of biocompatible piezo- and ferroelectric materials.

Molecularly Tunable Heterostructured Co-Polymers Containing Electron-Deficient and -Rich Moieties for Visible-Light and Sacrificial-Agent-Free H2O2 Photosynthesis.

As an alternative to hydrogen peroxide (H2O2) production by complex anthraquinone oxidation process, photosynthesis of H2O2 from water and oxygen without sacrificial agents is highly demanded. Herein, a covalently connected molecular heterostructure is synthesized via sequential C-H arylation and Knoevenagel polymerization reactions for visible-light and sacrificial-agent-free H2O2 synthesis. The subsequent copolymerization of the electron-deficient benzodithiophene-4,8-dione (BTD) and the electron-rich biphenyl (B) and p-phenylenediacetonitrile (CN) not only expands the π-conjugated domain but also increases the molecular dipole moment, which largely promotes the separation and transfer of the photoinduced charge carriers. The optimal heterostructured BTDB-CN0.2 manifested an impressive photocatalytic H2O2 production rate of 1920 µmol g-1 h-1, which is 2.2 and 11.6 times that of BTDB and BTDCN. As revealed by the femtosecond transient absorption (fs-TA) and theoretical calculations, the linkage serves as a channel for the rapid transfer of photogenerated charge carriers, enhancing the photocatalytic efficiency. Further, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) uncovers that the oxygen reduction reaction occurs through the step one-electron pathway and the mutual conversion between C=O and C-OH with the anchoring of H+ during the catalysis favored the formation of H2O2. This work provides a novel perspective for the design of efficient organic photocatalysts.

Modulating the Dipole Moment of Secondary Ammonium Spacers for Efficient 2D Ruddlesden-Popper Perovskite Solar Cells.

Layered two-dimensional (2D) perovskites are emerging as promising optoelectronic materials owing to their excellent environmental stability. Regulating the dipole moment of organic spacers has the potential to reduce the exciton binding energy (Eb ) of 2D perovskites and improve their photovoltaic performance. Here, we developed two azetidine-based secondary ammonium spacers with different electron-withdrawing groups, namely 3-hydroxyazatidine (3-OHAz) and 3,3-difluoroazetidine (3,3-DFAz) spacers, for 2D Ruddlesden-Popper (RP) perovskites. It was found that the large dipole moment of the fluorinated dipole spacer could effectively enhance the interaction between organic spacers and inorganic layers, leading to improved charge dissociation in 2D RP perovskite. In contrast to 3-OHAz spacer, the 2D perovskite using 3,3-DFAz as spacer also shows improved film quality, optimized energy level alignment, and reduced exciton binding energy. As a result, the 2D perovskite (n=4) device based on 3,3-DFAz yields an outstanding efficiency of 19.28 %, surpassing that of the 3-OHAz-Pb device (PCE=11.35 %). The efficiency was further improved to 19.85 % when using mixed A-site cation of MA0.95 FA0.05 . This work provides an effective strategy for modulating the energy level alignment and reducing the Eb by regulating the dipole moment of organic spacers, ultimately enabling the development of high-performance 2D perovskite solar cells.