Increasing Molecular Planarity through Donor/Side-Chain Engineering for Improved NIR-IIa Fluorescence Imaging and NIR-II Photothermal Therapy under 1064 nm

Developing conjugated small molecules (CSM) with intense NIR-II (1000-1700 nm) absorption for phototheranostic is highly desirable but remains a tremendous challenge due to a lack of reliable design guidelines. This study reports a high-performance NIR-II CSM for phototheranostic by tailoring molecular planarity. A series of CSM show bathochromic absorption extended to the NIR-II region upon the increasing thiophene number, but an excessive number of thiophene results in decreased NIR-IIa (1300-1400 nm) brightness and photothermal effects. Further introduction of terminal nonconjugated alkyl chain can enhance NIR-II absorption coefficient, NIR-IIa brightness, and photothermal effects. Mechanism studies ascribe this overall enhancement to molecular planarity stemming from the collective contribution of donor/side-chain engineering. This finding directs the design of NIR-II CSM by rational manipulating molecular planarity to perform 1064 nm mediated phototheranostic at high efficiency.

Automated summary

By tailoring molecular planarity, researchers have developed a high-performance conjugated small molecule (CSM) that absorbs in the near-infrared II (NIR-II) range for phototheranostic applications. Increasing the number of thiophene units extends the absorption to the NIR-II region, but excessive thiophene units result in decreased brightness and photothermal effects. Introducing a nonconjugated alkyl chain enhances the NIR-II absorption coefficient, brightness, and photothermal effects. This finding provides guidance for the design of NIR-II-absorbing CSMs through rational manipulation of molecular planarity.