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Issue 10, 2015
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Tuning the singlet-triplet energy gap: a unique approach to efficient photosensitizers with aggregation-induced emission (AIE) characteristics

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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 (ΔEST), 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 ΔEST 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 ΔEST 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.

Graphical abstract: Tuning the singlet-triplet energy gap: a unique approach to efficient photosensitizers with aggregation-induced emission (AIE) characteristics

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Supplementary files

Article information


Submitted
12 May 2015
Accepted
04 Jul 2015
First published
06 Jul 2015

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2015,6, 5824-5830
Article type
Edge Article

Tuning the singlet-triplet energy gap: a unique approach to efficient photosensitizers with aggregation-induced emission (AIE) characteristics

S. Xu, Y. Yuan, X. Cai, C. Zhang, F. Hu, J. Liang, G. Zhang, D. Zhang and B. Liu, Chem. Sci., 2015, 6, 5824
DOI: 10.1039/C5SC01733E

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