Phototheranostics represents a promising direction for modern precision medicine, which has recently attracted great research interest from multidisciplinary research areas. Organic optical agents including small molecular fluorophores, semiconducting/conjugated polymers, aggregation-induced emission luminogens, etc. with tuneable photophysical properties, high biosafety and biocompatibility, facile processability and ease of functionalization have delivered encouraging performance in disease phototheranostics. This review summarizes the recent progress of organic phototheranostic agents with an emphasis on the main strategies to manipulate the three excitation energy dissipation pathways, namely, radiative decay, thermal deactivation, and intersystem crossing, with the assistance of a Jablonski diagram, which particularly showcases how the Jablonski diagram has been guiding the design of organic agents from molecule to aggregate levels to promote the disease phototheranostic outcomes. Molecular design and nanoengineering strategies to modulate photophysical processes of organic optical agents to convert the absorbed photons into fluorescent/phosphorescent/photoacoustic signals and/or photodynamic/photothermal curing effects for improved disease phototheranostics are elaborated. Noteworthily, adaptive phototheranostics with activatable and transformable functions on demand, and regulation of excitation such as chemiexcitation to promote the phototheranostic efficacies are also included. A brief summary with the discussion of current challenges and future perspectives in this research field is further presented.

Organic near-infrared room temperature phosphorescence materials have unparalleled advantages in bioimaging due to their excellent penetrability. However, limited by the energy gap law, the near-infrared phosphorescence materials (>650 nm) are very rare, moreover, the phosphorescence lifetimes of these materials are very short. In this work, we have obtained organic room temperature phosphorescence materials with long wavelengths (600/657–681/732 nm) and long lifetimes (102–324 ms) for the first time through the guest-host doped strategy. The guest molecule has sufficient conjugation to reduce the lowest triplet energy level and the host assists the guest in exciton transfer and inhibits the non-radiative transition of guest excitons. These materials exhibit good tissue penetration in bioimaging. Thanks to the characteristic of long lifetime and long wavelength emissive phosphorescence materials, the tumor imaging in living mice with a signal to background ratio value as high as 43 is successfully realized. This work provides a practical solution for the construction of organic phosphorescence materials with both long wavelengths and long lifetimes.

The exciting applications of molecular motion are still limited and are in urgent pursuit, although some fascinating concepts such as molecular motors and molecular machines have been proposed for years. Utilizing molecular motion in a nanoplatform for practical application has been scarcely explored due to some unconquered challenges such as how to achieve effective molecular motion in the aggregate state within nanoparticles. Here, we introduce a class of near infrared-absorbing organic molecules with intramolecular motion-induced photothermy inside nanoparticles, which enables most absorbed light energy to dissipate as heat. Such a property makes the nanoparticles a superior photoacoustic imaging agent compared to widely used methylene blue and semiconducting polymer nanoparticles and allow them for high-contrast photoacoustic imaging of tumours in live mice. This study not only provides a strategy for developing advanced photothermal/photoacoustic imaging nanoagents, but also enables molecular motion in a nanoplatform to find a way for practical application.