Abstract
Using the electrospinning technique nanofibers consisting of organic nonlinear optical 3-nitroaniline (3NA, C6H6N2O2) nanocrystals embedded in poly-ε-caprolactone (PCL) polymer, 3NA@PCL nanofibers, were produced. Polarimetry optical second harmonic generation and X-ray diffraction studies show that 3NA push–pull molecules crystallize inside the polymer fibers with a strong preferential orientation giving rise to an alignment of the molecular dipole moments along the nanofibers longitudinal axis. This alignment strongly enhances the second order nonlinear optical response of the fibers. Intense second harmonic generation emission was observed from a single nanofiber, corresponding to an effective second order susceptibility of 80 pm V−1, four times greater than the largest second order susceptibility tensor element (21 pm V−1) associated with a macroscopic 3NA crystal. Moreover, when subjected to a modest periodically applied force of 3 N, a piezoelectric current of 70 nA generated by a 4 cm2 electrospun nanofiber mat amounted to 122 nW cm−2 of instantaneous density power, sufficient to power a LCD display. The results show that the electrospinning technique is a powerful technique to fabricate organic functional materials with oriented nanocrystals made of highly polarizable molecules, embedded in a polymer matrix.
Highlights
Low dimensional nanostructures in the form of bers, wires, rods, belts, tubes, and rings have attracted attention due to their novel properties and potential applications as sensors, exible electronic devices or nanogenerators of electrical energy
Compared to other methods of fabricating one-dimensional nanostructures, electrospinning is a simple and versatile technique capable of generating nano bers from a variety of polymers with embedded organic or semi-organic nanocrystals forming hybrid composite materials.1À3 The technique has recently been employed to organize nonlinear optical (NLO) chromophores into subwavelength scale architectures with rationally designed functionalities.[4,5,6,7,8]
Nitroaniline derivative molecules are known for their large microscopic molecular hyperpolarizabilities and for those crystallizing into an acentric point group, a large second harmonic generation (SHG) response has been measured for most of them
Summary
Low dimensional nanostructures in the form of bers, wires, rods, belts, tubes, and rings have attracted attention due to their novel properties and potential applications as sensors, exible electronic devices or nanogenerators of electrical energy. Nitroaniline derivative molecules are known for their large microscopic molecular hyperpolarizabilities and for those crystallizing into an acentric point group, a large second harmonic generation (SHG) response has been measured for most of them. In this work we report a strong polarized SHG response from a single electrospun nano ber formed by well-oriented 3NA organic nanocrystals embedded in poly-3-caprolactone (PCL) polymer. An effective second order susceptibility coef cient d3effNA@PCL 1⁄4 80 pm VÀ1 has been measured in a nano ber, which is four times larger than that reported for a macroscopic crystal This is the rst time 3NA high hyperpolarizable molecules have been integrated in functional nano bers and their crystalline nonlinear optical response studied. Upon applying a periodical force of 3 N to a 3NA@PCL nano ber mat, a piezoelectric current of 70 nA was generated with a maximum output power density of 122 nW cmÀ2. The sample mat is, previously to any measurements, checked for no short circuit between the electrodes
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