Elucidating the excited-state dynamics behavior in near-infrared Bodipy dye and aggregates toward biophotonics

Photo-induced excited-state dynamics within organic materials fundamentally determine their photophysical properties for various applications,and thus understanding the primary excited-state dynamics behavior is of fundamental and practical significance.Until recently,the excited-state dynamics of organic materials towards biophotonics have been rarely studied,although numerous endeavors have been devoted to the design of organic materials for biophotonics.Herein,various spectroscopy technologies including femtosecond transient absorption(fs-TA)spectroscopy clearly reveal a totally different excited state dynamics behavior within Bodipy monomer(2B-BDP dye)and aggregates(2B-BDP NPs),indicating strongly morphology dependent character.2B-BDP dye undergoes an ultrafast conversion from S1 to intramolecular charge transfer(ICT)state for subsequent photoluminescence(PL)and nonradiative(NR)decay,while 2B-BDP NPs show an accelerated excited-state deactivation mainly through S1→S0 NR decay.The potential bioapplications based on the corresponding excited state dynamics behavior are discussed together with experimental results.Interestingly,the accelerated NR decay in 2B-BDP NPs does not yield a stronger photoacoustic(PA)signal than that in 2B-BDP dye,which violates the conventional wisdom that faster NR decay would benefit the photothermal effects for better photoacoustic imaging(PAI).These insightful and fundamental observations of the excited-state dynamics may contribute an alternative approach at the molecular level towards the future design of functional Bodipy-based organic molecules with desirable performances.

Acceptor Engineering Produces Ultrafast Nonradiative Decay in NIR-Ⅱ Aza-BODIPY Nanoparticles for Efficient Osteosarcoma Photothermal Therapy via Concurrent Apoptosis and Pyroptosis

Small-molecule photothermal agents(PTAs)with intense second near-infrared(NIR-Ⅱ,1,000 to 1,700 nm)absorption and high photothermal conversion efficiencies(PCEs)are promising candidates for treating deep-seated tumors such as osteosarcoma.To date,the development of small-molecule NIR-Ⅱ PTAs has largely relied on fabricating donor–acceptor–donor(D–A–D/D′)structures and limited success has been achieved.Herein,through acceptor engineering,a donor–acceptor–acceptor(D–A–A′)-structured NIR-Ⅱ aza-boron-dipyrromethene(aza-BODIPY)PTA(SW8)was readily developed for the 1,064-nm laser-mediated phototheranostic treatment of osteosarcoma.Changing the donor groups to acceptor groups produced remarkable red-shifts of absorption maximums from first near-infrared(NIR-Ⅰ)regions(~808 nm)to NIR-Ⅱ ones(~1,064 nm)for aza-BODIPYs(SW1 to SW8).Furthermore,SW8 self-assembled into nanoparticles(SW8@NPs)with intense NIR-Ⅱ absorption and an ultrahigh PCE(75%,1,064 nm).This ultrahigh PCE primarily originated from an additional nonradiative decay pathway,which showed a 100-fold enhanced decay rate compared to that shown by conventional pathways such as internal conversion and vibrational relaxation.Eventually,SW8@NPs performed highly efficient 1,064-nm laser-mediated NIR-Ⅱ photothermal therapy of osteosarcoma via concurrent apoptosis and pyroptosis.This work not only illustrates a remote approach for treating deep-seated tumors with high spatiotemporal control but also provides a new strategy for building high-performance small-molecule NIR-Ⅱ PTAs.