Design of second near-infrared fluorescent molecules for disease phototheranostics

Phototheranostics that performs real-time diagnosis and concurrent in situ therapy upon non-invasive photoexcitation is rapidly emerging as a promising frontier, by virtue of its notable advantages including minimal toxicity, precise diagnosis imaging capability, satisfactory therapeutic effect, and negligible drug resistance. Of particular interest is single organic small molecules synchronously possessing powerful second near-infrared fluorescence imaging (NIR-II FLI) ability and prominent phototherapeutic outputs, owing to the high spatial resolution and imaging depth enabled by diminished tissue autofluorescence, reduced photon scattering, and low levels of photon absorption. Nevertheless, the development of such phototheranostic molecules with high performance remains a significant challenge, mainly because of the limitation of energy gap law (referring to that the nonradiative decay rate of an excited state increases exponentially as the energy gap between the excited and ground states decreases, and consequently presenting low-efficiency fluorescence brightness along with long emission wavelength), as well as the profoundly competitive energy dissipations in forms of each phototheranostic modality.