Highly Efficient Photosensitizers with Molecular Vibrational Torsion for Cancer Photodynamic Therapy

The development ofhighly effective photosensitizers (PSs) forphotodynamic therapy remains a great challenge at present. Most PSsrely on the heavy-atom effect or the spin-orbit charge-transferintersystem crossing (SOCT-ISC) effect to promote ISC, which bringsabout additional cytotoxicity, and the latter is susceptible to theinterference of solvent environment. Herein, an immanent universalproperty named photoinduced molecular vibrational torsion (PVT)-enhancedspin-orbit coupling (PVT-SOC) in PSs has been first revealed.PVT is verified to be a widespread intrinsic property of quinoid cyanine(QCy) dyes that occurs on an extremely short time scale (10(-10) s) and can be captured by transient spectra. The PVT property canprovide reinforced SOC as the occurrence of ISC predicted by the ElSayed rules ((1)& pi;& pi;*-(3)n & pi;*),which ensures efficient photosensitization ability for QCy dyes. Hence,QTCy7-Ac exhibited the highest singlet oxygen yield (13-fold higherthan that of TCy7) and lossless fluorescence quantum yield (& phi;(F)) under near-infrared (NIR) irradiation. The preeminent photochemicalproperties accompanied by high biosecurity enable it to effectivelyperform photoablation in solid tumors. The revelation of this propertysupplies a new route for constructing high-performance PSs for achievingenhanced cancer phototherapy. Photoinducedmolecular vibrational torsion-enhanced spin-orbitcoupling (PVT-SOC) in quinoid cyanine dyes has been revealed. Thisstrategy enables cyanine photosensitizers to have enhanced intersystemcrossing for cancer photodynamic therapy.