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01:26Photochemical Electrocyclic Reactions: Stereochemistry
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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
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01:21IR Absorption Frequency: Hybridization
1.5K
Hydrocarbons such as alkanes, alkenes, and alkynes show characteristic C–H stretching absorption bands. These IR stretching frequencies depend on the hybridization of the involved carbon atom and can be explained in terms of the s character of each hybridized atomic orbital.
Among the sp, sp2, and sp3 hybridized orbitals, sp orbitals have the maximum s character (50%). Consequently, the electrons are held more closely to the nucleus, resulting in stronger and shorter C–H bonds that...
Among the sp, sp2, and sp3 hybridized orbitals, sp orbitals have the maximum s character (50%). Consequently, the electrons are held more closely to the nucleus, resulting in stronger and shorter C–H bonds that...
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01:13¹H NMR: Complex Splitting
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A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
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01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
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Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
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01:37Super-resolution Fluorescence Microscopy
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Super-resolution fluorescence microscopy (SRFM) provides a better resolution than conventional fluorescence microscopy by reducing the point spread function (PSF). PSF is the light intensity distribution from a point that causes it to appear blurred. Due to PSF, each fluorescing point appears bigger than its actual size, and it is the PSF interference of nearby fluorophores that causes the blurred image. Various approaches to achieving higher resolution through SRFM have recently been...
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02:52Stereoisomerism
14.3K
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
14.3K
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Tuning Photophysical Conflict Into Synergy: Stereoelectronic Planarity Disruption Unlocks Concurrent
1State Key Laboratory of Flexible Electronics (LoFE) & Institute of Advanced Materials (IAM), School of Flexible Electronics (Future Technologies), Nanjing Tech University (NanjingTech), Nanjing, China.
Small (Weinheim an Der Bergstrasse, Germany)
|March 12, 2026
Summary
Researchers developed novel near-infrared-II fluorescent photosensitizers by disrupting molecular planarity, enhancing both fluorescence and reactive oxygen species generation upon aggregation. This breakthrough enables efficient tumor imaging and photodynamic therapy.
Area of Science:
- Materials Science
- Nanotechnology
- Biomedical Engineering
Background:
- Near-infrared-II (NIR-II) fluorescent photosensitizers face a trade-off where aggregation causes quenching of fluorescence and reactive oxygen species (ROS).
- This aggregation-caused quenching limits their efficacy in biomedical applications like photodynamic therapy (PDT).
Purpose of the Study:
- To overcome the aggregation-caused quenching in NIR-II photosensitizers.
- To develop a new molecular design strategy that enhances both fluorescence and ROS generation through aggregation.
- To create efficient NIR-II fluorescent nanoparticles for tumor theranostics.
Main Methods:
- Designed small molecules (AS4T, AS4Se) with disrupted stereoelectronic planarity using an acceptor-donor-acceptor-donor-acceptor (A-DA'D-A) scaffold.
- Integrated sterically demanding and electronically communicative peripheries.
- Characterized molecular properties using theoretical and structural analyses.
- Formulated nanoparticles (NPs) from the designed molecules.
Main Results:
- Achieved concurrent aggregation-enhanced ROS and fluorescence efficiencies by disrupting detrimental π-π interactions.
- AS4T NPs demonstrated a record-high singlet oxygen (1O2) quantum yield (24.7%) and robust superoxide radical (O2•-) production.
- AS4T NPs exhibited 6.3-fold higher NIR-II brightness compared to ICG/FBS.
- Demonstrated high-contrast tumor imaging and complete tumor elimination via photodynamic therapy using AS4T NPs under low-power laser irradiation.
Conclusions:
- Established a new design paradigm for NIR-II fluorescent photosensitizers by unifying aggregation-enhanced ROS and fluorescence.
- The developed strategy offers a transformative approach for highly efficient tumor phototheranostics.
- Disrupting molecular planarity is a key strategy to convert aggregation-caused quenching into an aggregation-enhanced process.