Modification of a SOCT-ISC type triphenylamine-BODIPY photosensitizer by a multipolar dendrimer design for photodynamic therapy and two-photon fluorescence imaging.

In this study, a series of multipolar triphenylamine-BODIPY photosensitizers T-BDPn (n = 1, 2, 3) was synthesized. Compared with T-BDP1 of D-A configuration, the multipolar T-BDP3 dendrimer have higher singlet oxygen efficiency (44%), better fluorescence quantum yield (7.45%), and could be used in the simulated photodynamic therapy in A-549 cells and two-photon fluorescence imaging in zebrafish. The theoretical calculation and fs-transient absorption spectra indicated that the reason of its higher singlet oxygen efficiency was that the multipolar T-BDP3 dendrimer could generate more nearly degenerate charge transfer (CT) states and triplet states, which could further increase the possibility of spin-orbit charge-transfer intersystem crossing (SOCT-ISC) process. In the simulated photodynamic therapy of A-549 cells, T-BDP3 shows good cytocompatibility, great phototoxicity with its IC50 value of 3.17 μM, and could kill cancer cells effectively with the dosage of 5 μM under 10 min irradiation in the AO/EB double-staining experiment. In the fluorescence imaging of zebrafish, the experiment results indicate that T-BDP3 could generate superoxide radical (O2˙-) in the body of zebrafish and could be applied to the two-photon fluorescence imaging under 800 nm excitation. The above experiment results shown that the multipolar dendrimer design was an effective approach to improve the key parameters of SOCT-ISC-type BODIPY photosensitizer and was ready for further two-photon photodynamic therapy in organisms.