Effective Light-Harvesting Antennae Based on BODIPY-Tethered Cardo Polyfluorenes via Rapid Energy Transferring and Low Concentration Quenching

Light-harvesting antennae (LHA) were demonstrated using polyfluorenes (PFs) modified with borondipyrromethene (BODIPY) dyes tethered to the cardo structures. PFs work as a light absorber and an energy donor to the BODIPY units. The series of BODIPY-tethering PFs via the cardo carbon including homocardo PFs and alternative polymers with fluorene and the cardo fluorene were synthesized, and their optical properties were investigated. Initially, highly efficient energy transferring was observed from the PF main chains to the BODIPY unit (99%). It was found that PFs can work as an efficient light absorber because of the large molar extinction coefficient and cause the rapid energy transfer through the cardo structure. Next, from the comparison with the emission efficiency of the BODIPY units in the series of the synthetic polymers, the favorable position of the BODIPY units was obtained to avoid the concentration quenching: The alternative polymer with cardo fluorene and dialkyl-substituted fluorene showed the largest emission efficiency in this study. Finally, we received the effective LHA with the 9 times larger amplification efficiency compared to that of the unimolar BODIPY unit. The results from the computer modeling suggest that the positions of the BODIPY units via the cardo structure could play a significant role in the inhibition of aggregation and electronic coupling with the BODIPY units, leading to the suppression of concentration quenching. Here is presented the feasibility of the cardo structure in fluorene as a scaffold for designing advanced optical materials.