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Updated: Feb 20, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Enhanced intersystem crossing in carbonylpyrenes.
Shinaj K Rajagopal1, Ajith R Mallia, Mahesh Hariharan
1School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Maruthamala P.O., Vithura, Thiruvananthapuram 695551, Kerala, India. mahesh@iisertvm.ac.in.
Carbonylpyrenes exhibit efficient triplet formation via ultrafast intersystem crossing (ISC), leading to high triplet quantum yields. This contrasts with pyrene, showing a new pathway for photophysical studies.
Area of Science:
- Photochemistry
- Spectroscopy
- Organic Chemistry
Background:
- Pyrene typically exhibits fluorescence as its dominant decay pathway.
- Carbonyl functionalization significantly alters the photophysical properties of pyrene derivatives.
Purpose of the Study:
- To investigate the ultrafast intersystem crossing (ISC) dynamics in carbonylpyrenes.
- To determine the mechanisms and efficiency of triplet state formation in these compounds.
Main Methods:
- Femtosecond pump-probe spectroscopy was employed to monitor transient species.
- Kinetic analysis of excited singlet and triplet state populations.
Main Results:
- Carbonylpyrenes show near-unity triplet formation upon photoexcitation.
- Rapid intersystem crossing (kISC) and internal conversion (kIC) occur within 5-11 ps.
- High triplet quantum yields (ΦT = 97%) were observed, exemplified by tetraacetylpyrene.
- Phosphorescence decay on a microsecond timescale indicates population of the emitter triplet state.
Conclusions:
- Ultrafast intersystem crossing is a dominant photophysical pathway for carbonylpyrenes.
- Carbonyl groups enhance triplet state formation efficiency compared to unsubstituted pyrene.
- These findings offer insights into controlling photophysical pathways for potential applications.
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