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  1. Abstract

    The fluorescence, phosphorescence, and photochemical properties of di‐ and triaryl‐substituted‐1,2,3‐triazoles are reported in this work. The ease of synthesis of regioisomers of substituted triazoles enables a systematic study on the correlation between regiochemistry and excited state properties, which include the solvent dependence of fluorescence, energy gap between singlet and triplet emitters, and propensity to photon‐triggered transformations. The triazoles that carry electron (e)‐donor and e‐acceptor aryl substituents show high fluorescence quantum yields in weakly polar solvents and exhibit solvent‐dependent fluorescence. The luminescence properties of these compounds in glass matrices at 77 K are characterized. The thermal and photo‐stability, two parameters that are crucial to their potential utilities in optical devices, of these compounds are determined. The position of the e‐donor substituent has a significant impact on the fluorescence emission energy and solvent sensitivity, singlet‐triplet energy gap, and photochemical reactivity and stability. The experimental observations on the structural correlation with the photophysical and photochemical properties are explained by quantum chemical calculations. This study provides a rationale on the placement of substituent on a donor‐acceptor type fluorophore to maneuver a range of photo‐related properties.

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  2. Although high piezoelectric coefficients have recently been observed in poly(vinylidene fluoride- co -trifluoroethylene) [P(VDF-TrFE)] random copolymers, they have low Curie temperatures, which makes their piezoelectricity thermally unstable. It has been challenging to achieve high piezoelectric performance from the more thermally stable PVDF homopolymer. In this report, we describe how high-power ultrasonic processing was used to induce a hard-to-soft piezoelectric transition and improve the piezoelectric coefficient d 31 in neat PVDF. After high-power ultrasonication for 20 min, a uniaxially stretched and poled PVDF film exhibited a high d 31 of 50.2 ± 1.7 pm V −1 at room temperature. Upon heating to 65 °C, the d 31 increased to a maximum value of 76.2 ± 1.2 pm V −1 , and the high piezoelectric performance persisted up to 110 °C. The enhanced piezoelectricity was attributed to the relaxor-like secondary crystals in the oriented amorphous fraction, broken off from the primary crystals by ultrasonication, as suggested by differential scanning calorimetry and broadband dielectric spectroscopy studies. 
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  3. An improved polymer has properties that make it competitive with commercially available ceramic piezoelectrics. 
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