Controlled molecular assemblies of chiral boron dipyrromethene derivatives for circularly polarized luminescence in the red and near-infrared regions

Chiral 1,1′-bi-2-naphthol (BINOL)-substituted boron dipyrromethene (BODIPY) derivatives with different numbers of phenyl groups at the 2 and 6 positions (denoted as nPh-B-BODIPY; n = 0, 1, 2) were newly synthesized to examine the aggregation-enhanced emission and circularly polarized luminescence (CPL) in the red and near-infrared (NIR) regions. Upon injection of THF solution of nPh-B-BODIPY into H₂O, 0Ph-B-BODIPY underwent controlled self-assembly to produce fibrous nanoarchitectures, whereas spherical nanoparticles were formed in 1Ph-B-BODIPY and 2Ph-B-BODIPY. Absorption and CD spectra of 0Ph-B-BODIPY nanofibers demonstrated a red-shifted and split spectrum corresponding to the 0-0 band, suggesting strong interaction between neighbouring 0Ph-B-BODIPY units. Such fibrous assemblies exhibited a broad emission spectrum with multiple bands ranging from the visible to the near-infrared (NIR) region due to the multiple aggregate states. Consequently, 0Ph-B-BODIPY nanofibers demonstrated a broad circularly polarized luminescence (CPL) spectrum in the red to NIR regions together with the enhanced dissymmetry factors (g_lum) relative to 0Ph-B-BODIPY (monomer) and 1Ph-B-BODIPY nanoparticles.