Tuning the singlet-triplet energy gap: a unique approach to efficient photosensitizers with aggregation-induced emission (AIE) characteristics
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Authors: | Shidang Xu Youyong Yuan Xiaolei Cai Chong-Jing Zhang Fang Hu Jing Liang Guanxin Zhang Deqing Zhang Bin Liu |
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Institution: | a Department of Chemical and Biomolecular Engineering , National University of Singapore , 4 Engineering Drive 4 , Singapore 117585 ; b Beijing National Laboratory for Molecular Sciences , Organic Solids Laboratory , Institute of Chemistry , Chinese Academy of Sciences , Beijing 100190 , China ; c Institute of Materials Research and Engineering , 3 Research Link , Singapore 117602 . Email: |
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Abstract: | The efficiency of the intersystem crossing process can be improved by reducing the energy gap between the singlet and triplet excited states (ΔE
ST), which offers the opportunity to improve the yield of the triplet excited state. Herein, we demonstrate that modulation of the excited states is also an effective strategy to regulate the singlet oxygen generation of photosensitizers. Based on our previous studies that photosensitizers with aggregation-induced emission characteristics (AIE) showed enhanced fluorescence and efficient singlet oxygen production in the aggregated state, a series of AIE fluorogens such as TPDC, TPPDC and PPDC were synthesized, which showed ΔE
ST values of 0.48, 0.35 and 0.27 eV, respectively. A detailed study revealed that PPDC exhibited the highest singlet oxygen efficiency (0.89) as nanoaggregates, while TPDC exhibited the lowest efficiency (0.28), inversely correlated with their ΔE
ST values. Due to their similar optical properties, TPDC and PPDC were further encapsulated into nanoparticles (NPs). Subsequent surface modification with cell penetrating peptide (TAT) yielded TAT–TPDC NPs and TAT–PPDC NPs. As a result of the stronger singlet oxygen generation, TAT–PPDC NPs showed enhanced cancer cell ablation as compared to TAT–TPDC NPs. Fine-tuning of the singlet-triplet energy gap is thus proven to be an effective new strategy to generate efficient photosensitizers for photodynamic therapy. |
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