A series of four lactose-modified BODIPY photosensitizers (PSs) with different substituents (-I, -H, -OCH3, and -NO2) in the para-phenyl moiety attached to the meso-position of the BODIPY core were synthesized; the photophysical properties and photodynamic anticancer activities of these sensitizers were investigated, focusing on the electronic properties of the different substituent groups. Compared to parent BODIPY H, iodine substitution (BODIPY I) enhanced the intersystem crossing (ISC) to produce singlet oxygen (1O2) due to the heavy atom effect, and maintained a high fluorescence quantum yield (ΦF) of 0.45. Substitution with the electron-donating methoxy group (BODIPY OMe) results in a significant perturbation of occupied frontier molecular orbitals and consequently achieves higher 1O2 generation capability with a high ΦF of 0.49, while substitution with the electron-withdrawing nitro group (BODIPY NO2) led a perturbation of unoccupied frontier molecular orbitals and induces a forbidden dark S1 state, which is negative for both fluorescence and 1O2 generation efficiencies. The BODIPY PSs formed water-soluble nanoparticles (NPs) functionalized with lactose as liver cancer-targeting ligands. BODIPY I and OMe NPs showed good fluorescence imaging and PDT activity against various tumor cells (HeLa and Huh-7 cells). Collectively, the BODIPY NPs demonstrated high 1O2 generation capability and ΦF may create a new opportunity to develop useful imaging-guided PDT agents for tumor cells.

We investigated the intramolecular charge transfer characteristics in the S 1 state of boron-dipyrromethene (BODIPY) derivatives with triphenylamine (TPA) substituents, depending on the substituted position and the number of substituents. Based on the spectroscopic and theoretical results, the β-substitution of TPA on BODIPY hybridizes locally excited and intramolecular charge transfer characteristics in the S 1 state because of strong coupling between the highest occupied molecular orbitals of BODIPY and TPA moieties, and consequently, the BODIPY derivatives with β-substituted TPAs exhibit strong red-color fluorescence around 640 nm in nonpolar and moderately polar solvents. The TPA substituent with propeller-like nonplanar geometry could prevent H-type aggregation between neighboring BODIPY derivative units and induce aggregation-induced emission enhancement (AIEE) characteristics of the BODIPY derivatives with TPA substituents, which are helpful to maintain their emission efficiencies under highly concentrated and condensed conditions. Since the red-color emission and AIEE property of the BODIPY derivatives with β-substituted TPAs are promising characteristics for a bioimaging application, we applied these derivatives to L-929 fibroblast cells for cellular imaging. The BODIPY derivative with a single β-substituted TPA (compound 2) was effectively loaded into porous silica nanoparticles (SNPs). Consequently, we achieved good cellular uptake of 2-SNPs and good cellular imaging, which further confirmed the bioimaging ability of 2-SNPs.

A series of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene-based photosensitizers (AmBXI, X = H, M, Br) featuring a cationic mitochondrion-targeting group and near-infrared (NIR) absorption was synthesized. After extending the photosensitizers’ π–π conjugation via Knoevenagel...