Related Experiment Video
Updated: Jun 27, 2026
06:08
Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera
Published on: December 27, 2018
Ultrafast Excited-State Dynamics and Two-Photon Near-Infrared Induced Photodynamic Therapy Performance of
Shuo Wang1, Qian Zhou1, Guang-Ning Pan1
1College of Chemistry, Beijing Normal University, Beijing 100875, China.
JACS Au
|June 26, 2026
Summary
This study introduces 5-Phenylethynyl-4-thiouridine (5ph-4TU) as a novel photosensitizer for deep-tissue cancer photodynamic therapy (PDT). Its unique structure enables enhanced two-photon absorption and efficient singlet oxygen generation for targeted cancer cell death.
Area of Science:
- Photochemistry
- Biophysics
- Medicinal Chemistry
Background:
- Conventional thio-nucleosides have limited UVA absorption for photodynamic therapy (PDT).
- Dual modifications like phenylethynyl and carbonyl-sulfur substitutions can enhance nucleoside photoactivity.
- Ultrafast excited-state dynamics of modified nucleosides are crucial for their photoactivity but remain underexplored.
Purpose of the Study:
- To investigate the excited-state dynamics and synergistic effects of dual modifications in 5-Phenylethynyl-4-thiouridine (5ph-4TU).
- To explore the potential of 5ph-4TU as a photosensitizer for deep-tissue cancer photodynamic therapy (PDT).
Main Methods:
- Ultrafast spectroscopy combined with QM-(MS-CASPT2//CASSCF)/MM calculations.
- Analysis of excited-state pathways, internal conversion, and intersystem crossing.
- In vitro biocompatibility and singlet oxygen generation assays.
- Two-photon irradiation experiments for cancer cell death induction.
Main Results:
- The C5-phenylethynyl group suppresses C5-C6 bond twisting, leading to a long-lived S2 (1ππ*) state (∼600 ps) with enhanced fluorescence (ΦFL = 0.11 ± 0.03).
- Efficient population of the triplet manifold occurs via S1 (1nπ*)/T2 (3ππ*)/T1 (3nπ*) quasi-degeneracy with significant spin-orbit coupling (SOC = 123 cm⁻¹).
- Extended π-conjugation enhances two-photon absorption in the near-infrared range, maintaining similar excited-state dynamics as single-photon excitation.
- In vitro studies confirmed excellent biocompatibility and efficient singlet oxygen (1O2) generation.
Conclusions:
- 5ph-4TU exhibits unique excited-state dynamics, including enhanced fluorescence and efficient triplet generation, due to its dual modifications.
- The compound demonstrates potential for deep-tissue PDT by inducing cancer cell death under two-photon irradiation (760-770 nm).
- 5ph-4TU represents a new paradigm for designing next-generation biophotosensitizers with combined imaging and therapeutic capabilities.
Related Concept Videos
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:23Photoluminescence: Fluorescence and Phosphorescence
Photoluminescence is a process where a molecule absorbs light energy and re-emits it in the form of light. This phenomenon occurs when a substance absorbs photons, promoting its electrons to higher energy level excited states, followed by a relaxation process in which the electrons return to their original ground state energy levels and emit light. Photoluminescence is widely observed in various materials, including semiconductors, and organic and inorganic compounds.
A pair of electrons in a...
A pair of electrons in a...
01:14Photoluminescence: Applications
Photoluminescence offers a wide range of applications due to its inherent sensitivity and selectivity. This technique allows for both direct and indirect analyses of the analyte. Direct quantitative analysis is possible when the analyte exhibits a favorable quantum yield for fluorescence or phosphorescence. However, an indirect analysis may be feasible if the analyte is not fluorescent or phosphorescent, or if the quantum yield is unfavorable. Indirect methods include reacting the analyte with...
01:26Variables Affecting Phosphorescence and Fluorescence
Fluorescence and phosphorescence are essential phenomena in fields like analytical chemistry, biological imaging, and materials science, where they detect molecular properties and visualize cellular structures. Understanding the variables that influence these luminescent behaviors is crucial for maximizing accuracy and efficiency in their applications. These variables can broadly be grouped into chemical structure, solvent properties, and external conditions, each playing a distinct role in...