Electrospun fibers with highly polarized second harmonic light from 2-amino-4-nitroaniline and 3-nitroaniline nanocrystals embedded in poly-L-lactic acid polymer

Abstract

Nanofibers consisting of organic optical nonlinear 2-amino-4-nitroaniline (2A4NA, C6H7N3O2) and 3-nitroaniline (3NA, C6H6N2O2) nanocrystals embedded in poly-L-lactic acid (PLLA) polymer were fabricated by the electrospinning technique. Intense anisotropic polarized second harmonic emission was observed from the molecular nanocrystals embedded within the nano and microfibers. The effective second-order susceptibility coefficients determined for the embedded 2A4NA and 3NA nanocrystals have magnitudes of 42 pmV-1 and 56 pmV-1 respectively, which are among the highest measured for organic nonlinear crystals. X-ray diffraction data revealed preferential crystallographic orientation of the molecules crystallized inside the nanofibers and calculations indicate average crystallite sizes of 33.5 nm and 21.7 nm, respectively for 2A4NA and 3NA. The present work follows previous studies on the nanofabrication, by the electrospinning technique, of polymer nanofibers doped with highly hyperpolarizable para-nitroaniline (C6H6N2O2) derivative push-pull molecules. These hybrid functional nano-systems display strong and directional nonlinear optical responses and establish the technique as a viable method for creating subwavelength scale generators of second harmonic light.