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This article provides a comprehensive overview of piezo-and ferro-electric materials based on organic molecules and organic-inorganic hybrids for mechanical energy harvesting. Molecular (organic and organic-inorganic hybrid) piezo-and ferroelectric materials exhibit significant advantages over traditional materials due to their simple solution-phase synthesis, light-weight nature, thermal stability, mechanical flexibility, high Curie temperature, and attractive piezo-and ferroelectric properties. However, the design and understanding of piezo-and ferroelectricity in organic and organic-inorganic hybrid materials for piezoelectric energy harvesting applications is less well developed. This review describes the fundamental characterization of piezo-and ferroelectricity for a range of recently reported organic and organic-inorganic hybrid materials. The limits of traditional piezoelectric harvesting materials are outlined, followed by an overview of the piezo-and ferroelectric properties of organic and organic-inorganic hybrid materials, and their composites, for mechanical energy harvesting. An extensive description of peptide-based and other biomolecular piezo-and ferroelectric materials as a biofriendly alternative to current materials is also provided. Finally, current limitations and future perspectives in this emerging area of research are highlighted. This perspective aims to guide chemists, materials scientists, and engineers in the design of practically useful organic and organic-inorganic hybrid piezo-and ferroelectric materials and composites for mechanical energy harvesting.

Two isostructural metal-organic framework (MOF) materials, namely, {[MeSi((3)Py)3]6(Cu6I6)}n (1) and {[ MeSi((3)Qy)3]6(Cu6I6)}n (2), featuring Cu6I6 clusters were synthesized from tridentate arylsilane ligands of the type MeSi((3)Py)3 ((3)Py = 3-pyridyl) and MeSi((3)Qy)3 ((3)Qy = 3-quinolyl), respectively. While the MOF 1 displays the usual thermochromism associated with traditional Cu4I4Py4 clusters, the MOF 2 shows (3)XLCT/(3)MLCT emission due to the Cu6I6 cluster core at both 298 and 77 K, albeit with some marginal variations in its emission wavelengths. Interestingly, an unusual reversal in the mechanochromic luminescent behavior was observed for these isostructural MOFs at 298 K wherein a pronounced blue-shifted high energy emission for 1 (from orange to yellowish-orange) and a red-shifted low-energy emission for 2 (from green to orange) were obtained upon grinding these samples. This is primarily due to the variations in their cuprophilic interactions as 1 displays shorter Cu···Cu distances (2.745(1) Å) in comparison with those present in 2 (3.148(0) Å). As a result, the ground sample of 2 exhibits a prominent red shift in luminescence owing to the reduction of its Cu···Cu distances to an unknown value closer to the sum of van der Waals radii between two Cu(I) atoms (2.80 Å). However, the blue-shifted emission in 1 is presumably attributed to the rise in its lowest unoccupied molecular orbital energy levels caused by changes in the secondary packing forces. Furthermore, the absorption and emission characteristics of 1 and 2 were substantiated by time-dependent density functional theory calculations on their discrete-model compounds. In addition, the syntheses, reactivity studies, and photophysical properties of two one-dimensional MOFs, namely, {[MeSi((3)Qy)3]2(Cu2I2)}n (3) and {[MeSi((3)Qy)3](CuI)}n (4), having dimeric Cu2I2 and monomeric CuI moieties, respectively, were examined.

The reaction of LH3 with Ni(ClO4)(2).6H 2O and lanthanide salts in a 2:2:1 ratio in the presence of triethylamine leads to the formation of the trinuclear complexes [L2Ni2Ln][ClO4] (Ln=La (2), Ce (3), Pr (4), Nd (5), Sm (6), Eu (7), Gd (8), Tb (9), Dy (10), Ho (11) and Er (12) and L: (S)P[N(Me)NCH-C6H3-2-O-3-OMe]3). The cationic portion of these complexes consists of three metal ions that are arranged in a linear manner. The two terminal nickel(II) ions are coordinated by imino and phenolate oxygen atoms (3N, 3O), whereas the central lanthanide ion is bound to the phenolate and methoxy oxygen atoms (12O). The Ni-Ni separations in these complexes range from 6.84 to 6.48 A. The Ni-Ni, Ni-Ln and Ln-O phenolate bond distances in 2-12 show a gradual reduction proceeding from 2 to 12 in accordance with lanthanide contraction. Whereas all of the compounds (2-12) are paramagnetic systems, 8 displays a remarkable ST=(11)/2 ground state induced by an intramolecular Ni. . .Gd ferromagnetic interaction, and 10 is a new mixed metal 3d/4f single-molecule magnet generated by the high-spin ground state of the complex and the magnetic anisotropy brought by the dysprosium(III) metal ion.

Hybrid lead halide perovskites have emerged as an important class of optoelectronic materials. A creative choice of "A"-site organic cations produces hybrid perovskites with reduced dimensionality and intriguing light−matter interactions. Nonlinear optical effects are expected to be stronger in one-dimensional (1D) lead halides compared to those in their 2D or 3D analogues due to greater quantum and dielectric confinements. We performed an extensive probe of the third harmonic generation (THG) properties in 1D pyridinium lead iodide single crystals for the first time. An efficient THG with a high laser-induced damage threshold is the highlight of this system. THG is selectively enhanced for excitation at an optical communication wavelength (1.5 μm) corresponding to band gap resonance. A strong exciton−phonon interaction results in highly Stokes-shifted self-trapped excitonic emission in the 5−300 K temperature range. An interplay between anharmonicity and dynamic disorder dictates the emission properties, further complicated by an isostructural phase transition at 170 K.

A sterically hindered aryl phosphonic acid ArP(O)(OH)2 (2) (Ar = 2,4,6-isopropylphenyl) was synthesized and structurally characterized. ArP(O)(OH)2 forms an interesting hydrogen-bonded corrugated sheet-type supramolecular structure in the solid-state. A three-component reaction involving ArP(O)(OH)2, 3,5-dimethylpyrazole(DMPZH), and Cu(CH3COO)2.H2O produces the tetranuclear Cu(II) compound [Cu4(mu3-OH)2{ArPO2(OH)}2(CH3CO2)2(DMPZH)4][CH3COO]2.CH2Cl2 (3). A similar three-component reaction involving ArP(O)(OH)2, 3,5-dimethylpyrazole, and Zn(CH3COO)2.2H2O yields the tetranuclear Zn(II) compound [Zn4{ArPO3}2{ArPO2(OH)}2{DMPZH}4(DMPZ)2].5MeOH (4). While 3 has been found to have an asymmetric cage structure where two dinuclear copper cores are bridged by bidentate [ArPO2(OH)]- ligands, 4 possesses an open-book tricyclic structure composed of three fused metallophosphonate rings. Magnetic studies on 3 revealed antiferromagnetic behavior.

Organotin clusters and cages have been synthesized in quantitative yields by using a benign solventless synthetic methodology. Using this method a variety of structural forms, which include the drum, O-capped cluster, tetranuclear oxo cage, discrete, and polymeric compounds, have been synthesized. All these compounds (1-11) have been characterized by spectroscopic and analytical techniques. The new compounds, which include the hexameric drum [n-BuSn-(O)OCOAd] 6 (Ad ) adamantyl) 9, a triorganotin-based discrete structure Ph 3 SnO 2 C-C 6 H 2 -2,4,6-Me 3 (10), and a polymer Ph 3 SnOSO 2 -C 6 H 3 -2,5-Me 2 (11), have been characterized by single-crystal X-ray crystallography. § This paper is dedicated to Prof. R. R. Holmes on the occasion of his 75th birghday.

Two new molecular organic−inorganic hybrid halogenometallates [BnNMe 2 R]CdBr 4 (Bn = benzyl; 1: R = Me; 2: R = n-Pr) have been synthesized and found to crystallize in the acentric crystal systems suitable for ferroelectric behavior. Both these compounds exhibit well-resolved rectangular polarization vs electric field (P−E) hysteresis loops at room temperature for their polycrystalline thin films. Compounds 1 and 2 exhibited fairly high remnant polarization (P r ) values of 18.59 and 14.24 μC cm −2 , respectively. Moreover, flexible composite thin films of these halogenometallate salts with poly-(dimethylsiloxane) (PDMS) were prepared and employed as mechanical energy-harvesting devices using an impact test setup operating at a frequency of 25 Hz and an applied force of 40 N. The maximum output voltages of 52.9 and 63.8 V have been recorded for the PDMS-fabricated devices of 5 wt % of 1 and 10 wt % of 2, respectively. Also, the obtained power densities of 13.8 and 37.1 μW cm −2 for the respective 5 wt % 1−PDMS and 10 wt % 2−PDMS devices are much higher than all known devices made up of organic− inorganic hybrid materials embedded in PDMS. The energy harvested from these devices was further utilized to charge a capacitor through a full wave-bridge rectifier.