Hybrid organic–inorganic perovskites (HOIPs) have garnered widespread interest, yet stability remains a critical issue that limits their further application. Compared to their three-dimensional (3D) counterparts, two-dimensional (2D)-HOIPs exhibit improved stability. 2D-HOIPs are also appealing because their structural and optical properties can be tuned according to the choice of organic ligand, with monovalent or divalent ligands forming Ruddlesden–Popper (RP) or Dion–Jacobson (DJ)-type 2D perovskites, respectively. Unlike RP-type 2D perovskites, DJ-type 2D perovskites do not contain a van der Waals gap between the 2D layers, leading to improved stability. However, bifunctional organic ligands currently used to develop DJ-type 2D perovskites are limited to commercially available aliphatic and single-ring aromatic ammonium cations. Large conjugated organic ligands are in demand for their semiconducting properties and their potential to improve materials stability further. In this manuscript, we report the design and synthesis of a new set of larger conjugated diamine ligands and their incorporation into DJ-type 2D perovskites. Compared with analogous RP-type 2D perovskites, DJ 2D perovskites reported here show blue-shifted, narrower emissions and significantly improved stability. By changing the structure of rings (benzene vs thiophene) and substituents, we develop structure–property relationships, finding that fluorine substitution enhances crystallinity. Single-crystal structure analysis and density functional theory calculations indicate that these changes are due to strong electrostatic interactions between the organic templates and inorganic layers as well as the rigid backbone and strong π–π interaction between the organic ligands themselves. These results illustrate that targeted engineering of the diamine ligands can enhance the stability of DJ-type 2D perovskites.

minimizing power consumption. Photonic nanostructures and thin films are prime candidates to meet these requirements.Barium titanate (BaTiO 3 ) is a ferro electric with a large Pockels coefficient, low optical loss, and fast response. [3] However, it remains challenging to integrate the BaTiO 3 materials with photonic structures on a single chip because of the mismatch of the crystal properties with the photonic structure, which renders attempts at heter ogenous integration costly and complex.BaTiO 3 nanoparticles, processed from solution, allow uniform films to be inte grated onto photonic structures via wet deposition methods, such as spin coating, drop casting, and spray pyrolysis, thereby simplifying the manufacturing process of onchip EO modulators. [4] When the particle size is reduced in this way, how ever, a lower EO response is seen. [5] We investigated whether doping could overcome the limitations of solutionprocessed ABO 3 perov skite nanoparticles such as BaTiO 3 . [6] Rareearth ions such as La 3+ and Er 3+ have been used to substitute the Ba site as donors, while transition metals Mn 2+ and Ni 2+ favor the Ti site as accep tors. Both donor and acceptor doping have been studied in view of their potential to improve the dielectric constant and spontaneous polarization. [7] Since EO response is proportional to spontaneous polarization and dielectric constant, [8] doping appears to have the potential to enhance EO. Results and DiscussionWe used an ethanol dispersion with 20 wt% of BaTiO 3 nano particles to fabricate films (Experimental Section). The average nanoparticle diameter is 200 nm, sufficient to support the tetragonal phase. [9] We used atomic force microscopy (AFM) to measure the surface topography and thickness of the BaTiO 3 nanoparticle films: this revealed a thickness of 700 nm and a rootmeansquare of 25 nm (Figure S1, Supporting Information). The optical transmission spectra of the BaTiO 3 nano particle films were recorded using a UV-vis-NIR (near infrared) spectrometer (Figure S2a, Supporting Information). Spincast films exhibit transmission of 85% in the wavelength range between 400 and 2000 nm. The refractive index of the Electro-optic (EO) modulators provide electrical-to-optical signal conversion relevant to optical communications. Barium titanate (BaTiO 3 ) is a promising material system for EO modulation in light of its optical ultrafast nonlinearity, low optical loss, and high refractive index. To enhance further its spontaneous polarization, BaTiO 3 can be doped at the Ba and Ti sites; however, doping is often accompanied by ion migration, which diminishes EO performance. Here, donor-acceptor doping and its effect on EO efficiency are investigated, finding that La-doped BaTiO 3 achieves an EO coefficient of 42 pm V −1 at 1 kHz, fully twice that of the pristine specimen; however, it is also observed that, with this single-element doping, the EO response falls off rapidly with frequency. From impedance spectroscopy, it is found that frequency-dependent EO is correlated with ion mig...

We switch the molecule from SHG inert to SHG active by controlling the degree of hydrogen bonding through protonation.

Piezoelectric materials convert between mechanical and electrical energy and are a basis for self-powered electronics. Current piezoelectrics exhibit either large charge (d33) or voltage (g33) coefficients but not both simultaneously, and yet the maximum energy density for energy harvesting is determined by the transduction coefficient: d33*g33. In prior piezoelectrics, an increase in polarization usually accompanies a dramatic rise in the dielectric constant, resulting in trade off between d33 and g33. This recognition led us to a design concept: increase polarization through Jahn-Teller lattice distortion and reduce the dielectric constant using a highly confined 0D molecular architecture. With this in mind, we sought to insert a quasi-spherical cation into a Jahn-Teller distorted lattice, increasing the mechanical response for a large piezoelectric coefficient. We implemented this concept by developing EDABCO-CuCl4 (EDABCO = N-ethyl-1,4-diazoniabicyclo[2.2.2]octonium), a molecular piezoelectric with a d33 of 165 pm/V and g33 of ~2110 × 10−3 V m N−1, one that achieved thusly a combined transduction coefficient of 348 × 10−12 m3 J−1. This enables piezoelectric energy harvesting in EDABCO-CuCl4@PVDF (polyvinylidene fluoride) composite film with a peak power density of 43 µW/cm2 (at 50 kPa), the highest value reported for mechanical energy harvesters based on heavy-metal-free molecular piezoelectric.