Electrospun polyfunctional switch-typed anisotropic photoconductive film endued with superparamagnetic-fluorescent performances

Abstract

A new concept of switch-typed anisotropic photoconductive film (named as SAPF) is proposed for the first time. SAPF with top-bottom structure is constructed by electrospinning via using 2,7-dibromo-9-fluorenone (DF) of both fluorescence and photoconductivity as luminescent and conductive material. [High concentration DF (H-DF)/polyvinylidene fluoride (PVDF)/polyvinylpyrrolidone (PVP)]//[Fe3O4/PVDF/PVP] Janus nanofibers and [low concentration DF (L-DF)/polymethylmethacrylate (PMMA)] nanobelts are used as building units to respectively construct the arrayed top layer and non-arrayed bottom layer. In the absence of light irradiation, only the top layer is superparamagnetic. Under 275-nm or 290-nm ultraviolet light illumination, the bottom layer emits fluorescence, and the top layer has three properties of anisotropic conductivity, fluorescence and superparamagnetism, meaning that SAPF realized the conversion from mono-function to tri-function via without to with light irradiation. PVDF with piezoelectric property can promote the photoconductive effect of DF. Through the transition from light illumination to without light illumination, the current in conductive direction of SAPF increases from 7.147 × 10−4 to 0.807 μA and the degree of anisotropy reaches 1.958 × 103. Fluorescence colors from green to blue can be modulated by adjusting the concentration and existing environment of fluorenone and excitation wavelength. Janus nanofiber ensures high anisotropic photoconduction and fluorescence of SAPF. SAPF displays excellent photoconduction, superparamagnetism and tunable fluorescence upon light illumination. The design idea and preparation process provide guidance for the development of new anisotropic photoconductive films with polyfunctions.