Effect of molecular packing on modulation of electronic properties of organic donor–acceptor hybrid gels

Abstract

Here we report gelation properties and molecular packing of phenyl alanine conjugated perylenebisimide (PPA, P) in dimethyl formamide (DMF) and tetrahydrofuran (THF). In both solvents, PPA self-assembles to crystalline nanofibers and exhibits solvent dependent packing polymorphism of PPA molecule. The gels reveal almost comparable optoelectronic behavior in solutions, but xerogels prepared from P3TAA-PPA hybrid(PP), (a donor-acceptor system) in THF exhibits four times higher conductivity than that in DMF and 12 times higher conductivity in former than the later on illumination with light of 1 sun. Spectroscopy, microscopy, X-ray scattering and electrical measurements suggest that the robust crystalline packing of PPA in THF compare to DMF results in better percolation of charges. Due to different packing arrangement, PP-THF hybrid xerogel exhibits negative differential resistance whereas PP-DMF xerogel acts as electronic memory.The impedance results indicate lower charge transfer resistance and higher capacitance in P-THF than in P-DMF xerogel for the difference of molecular packing and this is also greatly reflected in hybrid xerogels. This study proves that although different packing of PBI may have small effect in optical properties and conductivity of pristine assemblies, but such packing differences are critical in determining the efficiency of charge transport when incorporated into donor-acceptor composites.