Size-tunable exciton chirality and fluorescence emission in ( R)-(−)-2,2′-bis-( p-toluenesulfonyloxy)-1,1′-binaphthalene nanoparticles

Abstract

The organic nanoparticles from a chiral auxiliary, ( R)-(−)-2,2′-bis-( p-toluenesulfonyloxy)-1,1′-binaphthalene (R-BTBN), were fabricated with a range of particle size from 40 to 160 nm through the reprecipitation method. The exciton chirality and the fluorescence emission of the particles display size-tunable behaviors. The circular dichroism (CD) spectra of the nanoparticles experience a bathochromic shift with an increase in the particle size and the intensity ratio of the first to the third cotton effect (CE) increases as the nanoparticle size increases to 60 nm. And also the nanoparticles show excimer emission that enhances as the particle size grows. CD spectra accompanied with UV, fluorescence emission spectra, reveal that the size-tunable optical properties are attributed to the synergetic effect of the change of dihedral angle in the initial stage and the more effective formation of excimer between the two naphthalene chromophores in adjacent molecules as nanoparticles grow.