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Structural disorder as a key to photoprotection in eumelanin multimers
Kavya Vinod1, Diana Thomas1, Mahesh Hariharan1
1School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram (IISER TVM) Maruthamala P.O., Vithura Thiruvananthapuram 695551 Kerala India mahesh@iisertvm.ac.in.
Chemical Science
|July 14, 2025
Summary
Eumelanin multimers show broader absorption and faster energy relaxation with increased size. Excitonic interactions in these model systems explain the pigment
Area of Science:
- Photophysics
- Biomaterials Science
- Spectroscopy
Background:
- Eumelanin, a natural pigment, offers UV protection by dissipating energy.
- Mechanisms of eumelanin's broad absorption and rapid energy relaxation are not fully understood due to its complex structure.
Purpose of the Study:
- To investigate the optical properties of model eumelanin multimers (monomer, dimer, trimer).
- To elucidate the role of multimer size and aggregation in eumelanin's photophysical behavior.
- To understand the contribution of excitonic interactions to energy dissipation.
Main Methods:
- Synthesis and characterization of eumelanin model multimers: DMICE (monomer), DMICE-D (dimer), and DMICE-T (trimer).
- Optical property measurements in solution and thin films.
- Analysis of excited state dynamics and excitonic couplings.
Main Results:
- Increased multimer size and aggregation broaden absorption spectra due to amplified excitonic interactions.
- Non-radiative decay processes (internal conversion, intersystem crossing) become more efficient with longer multimers.
- Eumelanin dimers and trimers in thin films show ultrafast excited state relaxation (<30 ps) via internal conversion.
Conclusions:
- Structural organization and excitonic interactions are key to eumelanin's photophysical properties.
- Model eumelanin multimers replicate the ultrafast energy dissipation of natural eumelanin.
- Findings advance the development of eumelanin-inspired biomimetic materials for photoprotection.
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