Manipulating Nonradiative Decay Channel by Intermolecular Charge Transfer for Exceptionally Improved Photothermal Conversion

Abstract

In-depth studies of nonradiative (NR) decay, seeking to maximize NR decay rate or manipulate other NR decay channels, are of greatest significance for improving the photothermal conversion efficiency (η) of organic materials for phototheranostics; however, to date, relevant work remains scarce. Here, we present an insightful study of NR decay in BODIPY (BDP) dye, in an aggregated state, i.e., in BDP nanoparticles (BDP NPs), which show an efficient additional NR decay channel from the aggregation-stabilized intermolecular charge transfer (CT) state, resulting in exceptionally high η (61%) for highly efficient phototheranostics in vivo. BDP NPs exhibit two ultrafast NR decay channels with ultrashort lifetimes of 1.7 and 50 ps, which is in stark contrast to the only S 1 → S 0 NR channel with a long lifetime of 373 ps in the isolated BDP dye. More importantly, the ultrafast NR channel (1.7 ps) in BDP NPs depletes a substantial portion of the excited-state population (71%), which accounts for its much better photothermal effect as compared with the isolated BDP dye. Finally, BDP NPs display a highly efficient photoacoustic imaging (PAI) guided photothermal therapy (PTT) of tumors in live mice. This study presents a deeper fundamental understanding of NR decay in organic materials, setting a valuable guideline that may be widely applicable to similar molecular structure to develop more advanced organic materials not only for photothermal-related applications.

Photochemical Synthesis of Nonplanar Small Molecules with Ultrafast Nonradiative Decay for Highly Efficient Phototheranostics

“…As presented in Figure 3i,j, within the first‐picosecond time, the signal at around 385 nm shows apparent decay, accompanied by a new signal increase at about 584 nm. The result from fs‐TA spectroscopy is similar to that in the previous report, [ 25 ] so it can be inferred that there is also a charge transfer state in NSMN. The fitting kinetic decay curves at 830 nm are presented in Figure 3k.…”

Structural and process controls of AIEgens for NIR-II theranostics

“… 87 Fan and co-workers boosted nonradiative decay channel through manipulating intermolecular charge transfer, attaining an exceptionally high PCE of 61%. 88 Lee and co-workers reported a kind of π-conjugated oligomer F8-IC linked with A–D–A structure, whose intramolecular flexible rotations led to an enhanced non-radiative decay. The resulting F8-IC NPs displayed a high PCE of 82% for high-performance PA imaging-guided cancer therapy.…”

Tuning Optical Properties of BODIPY Dyes by Pyrrole Conjugation for Photoacoustic Imaging

“…Here, we aim to optimize highly biocompatible and photostable BODIPY dyes [ 26 ] for PAI applications. The BODIPY probes were already explored in PAI including PTT, [ 27 ] and to generate photodynamic effect. [ 28 ] The 3,5‐bis‐ p ‐methoxystyryl BODIPY was the first example studied in PAI, [ 29 ] but required laser energies to generate a PA signal outside of the clinically acceptable range.…”