Singlet fission in colloid nanoparticles of amphipathic 9,10-bis(phenylethynyl)anthracene derivatives

Abstract

Three 9,10-bis(phenylethynyl) anthracene derivatives with zero (BPEA), one (BPEA-COOH) and two (BPEA-(COOH)2) carboxylic groups are synthesized and prepared into colloidal nanoparticles in the aqueous solution. Scanning electron microscopy shows different morphologies of these three nanoparticles due to the different driving forces for the self-assembly process. Steady-state absorption and fluorescence spectra reveal the presence of the strong intermolecular interaction between the adjacent anthracene units in these three nanoparticles, and the interactions in BPEA-COOH and BPEA-(COOH)2 nanoparticles are larger than that in BPEA. Singlet fission (SF) could be conducted in these three nanoparticles as revealed by the transient absorption experiment, but with different efficiencies. Triplet yields of BPEA-COOH (109%) and BPEA-(COOH)2 (98%) nanoparticles decreased a lot compared to that of BPEA nanoparticles (122%), which is caused by the more endothermic SF in BPEA-COOH and BPEA-(COOH)2 nanoparticles due to the decreased singlet state energy.