Side‐Chain‐Tuned Molecular Packing Allows Concurrently Boosted Photoacoustic Imaging and NIR‐II Fluorescence

Abstract

It is generally considered that photoacoustic imaging (PAI) and fluorescence imaging (FLI) cannot be enhanced concurrently, as they are dependent on competitive photophysical processes at the single-molecule level. Herein, we reveal that BDTR9-OC8 and BDTR9-C8, which have identical π-conjugated backbones but are substituted by side chains of different rigidity, show distinct phototheranostic properties in the aggregated state. The NIR-II FLI and PAI brightness of BDTR9-C8 nanoparticles are enhanced by 4.6 and 1.4 times compared with BDTR9-OC8 nanoparticles. Theoretical calculations and GIWAXS analysis revealed that BDTR9-C8 with rigid side chains shows a relative amorphous condensed state, which will benefit the efficient transportation of photo-generated excitons and phonons, subsequently enhancing the FLI and PAI signals. Besides, both nanoparticles exhibit excellent photothermal conversion efficiency due to their strong light-harvesting capability and are considered effective photothermal therapy materials. This work provides an illuminating strategy for material design in the future.

Organic conjugated small molecules with donor–acceptor structures: design and application in the phototherapy of tumors

“…[175][176][177] In addition, Tian's group systematically studied the effects of the side chains in Y-series photosensitizers on their PTT performance. 178 The flexible side chains are more facile to rotate than the rigid side chains, which have big effects on the photothermal conversion. As the steric hindrance of the side chains was increased, the nanoparticles based on the corresponding photosensitizers showed a gradually decreasing PTCE.…”

Effective design of organic luminogens for near-infrared-II fluorescence imaging and photo-mediated therapy

“…This difference was greatly attributed to the rigidity of the side chain which was essential in attaining the simultaneous improvement of PAI and FLI. 88…”

“…For example, PAI as a result of non-radiation probability has been reported to provide up to 5-7 cm depth of tissue imaging with a high spatial resolution. 88 Organic dyes, metallic nanoparticles, carbon nanotubes, and 2D materials are among the commonly used PAI agents. However, such materials have inherent flaws such as poor photostability and biocompatibility.…”

A nanoplatform for mild-temperature photothermal and type I & II photodynamic therapy in the NIR-II biowindow

“…1). Benefiting from strong D-A effects, [31][32][33][34] DPTTIC showed a broad range of wavelengths of light absorbed and a narrow bandgap. Considering the hydrophobicity of DPTTIC, we synthesized a new amphiphilic pillararene, denoted as WP5-8C-2PEG, which can self-assemble in water and hence in this way be used as nanocarriers.…”

“…S14b, ESI †), which resulted in good non-radiative decay. 33 In addition, the energy gap between its singlet state (S 1 ) and triplet state (T 1 ) was calculated to be 0.50 eV (Fig. S14c, ESI †), a small value favourable for achieving excellent PDT activity.…”