Self-assembly of tetraphenylethylene-based dendron into blue fluorescent nanoparticles with aggregation induced enhanced emission${}^{\S }$

Luminescent organic nanoassemblies have received great attention in recent years due to their potential applications in material science and bioimaging. Since most of the fluorophores undergo aggregation-caused quenching in the solid state, their technological applications are limited. Hence, there is a high demand for the design of fluorophores which show enhanced emission in the aggregated and solid states. Herein we report the design and synthesis of a tetraphenylethylene based dendron through multistep organic reactions. Very weak emission is observed for the dendron in the molecularly dissolved state, which is attributed to the rotational relaxation of intramolecular $\text{C}\left({\text{sp}}^2\right)$–$\text{C}\left({\text{sp}}^2\right)$ bond rotation in the excited state. The aggregates of the dendron are prepared with the addition of a 'poor' solvent into a solution of the dendron in a 'good' solvent. A huge enhancement in fluorescence is observed in the aggregated state, which is attributed to the restriction of intramolecular $\text{C}\left({\text{sp}}^2\right)$–$\text{C}\left({\text{sp}}^2\right)$ bond rotation and makes the radiative decay as the main decay channel for the aggregated state. The induced self-assembly of the dendron with the addition of 'poor' solvent results in the formation of emissive nanoparticles. We hope the blue emissive nanoparticles may find applications in material science and bioimaging.

Graphical Abstract

SYNOPSIS Synthesis of a new tetraphenylethylene-based dendron using multistep organic reactions is reported. Self-assembly of the dendron into nanoparticles is achieved with the addition of a "poor" solvent (water) into a solution of the dendron in "good" solvent (DMSO). A strong aggregation induced enhanced emission is observed for the nanoparticle due to the restriction of intramolecular $\text{C}\left({\text{sp}}^2\right)$–$\text{C}\left({\text{sp}}^2\right)$ bond rotation in the aggregated state. .