Modulating Heavy-Atom-Free Triplet-State Dynamics in Benzimidazole-Based D-π-A Molecules: Distinct Roles of Solvent
Yang Liu1, Tiantian Guan1, Beidou Feng1
1Henan Key Laboratory of Infrared Materials & Spectrum Measures and Applications, School of Optoelectronic Engineering, School of Physics, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang453007, P. R. China.
The Journal of Physical Chemistry Letters
|August 13, 2026
Summary
Heavy-atom-free organic molecules can efficiently generate triplet states using nitro substitution. Solvent polarity and hydrogen bonding significantly influence intersystem crossing and triplet state lifetimes for photonic applications.
Area of Science:
- Organic Photochemistry
- Materials Science
Background:
- Efficient triplet-state generation is crucial for organic photonic applications.
- Heavy-atom-free organic molecules are sought after to avoid heavy metal toxicity and cost.
- Benzimidazole-based donor-π-acceptor (D-π-A) molecules are promising candidates.
Purpose of the Study:
- Investigate triplet exciton dynamics in benzimidazole D-π-A molecules with varying acceptor groups (-OH, -NO2, -C(CN)2).
- Determine the influence of solvent polarity and protic/aprotic nature on intersystem crossing (ISC) and triplet-state lifetimes.
- Elucidate the mechanisms behind efficient triplet generation in these systems.
Main Methods:
- Transient absorption spectroscopy to study exciton dynamics.
- Synthesis of benzimidazole-based D-π-A molecules with -OH, -NO2, and -C(CN)2 acceptors.
- Theoretical calculations (e.g., DFT) to understand electronic transitions and ISC pathways.
Main Results:
- Nitro-substituted BVI-NO2 showed efficient ISC (863.4 ps) and triplet population (1.53 μs) in DMSO.
- Aprotic solvents prolonged ISC times and shortened triplet decay with decreasing polarity.
- Protic solvents significantly accelerated ISC and shortened triplet lifetimes due to hydrogen bonding.
- Theoretical calculations revealed a favorable S1(π, π) → T4(n, π*) transition for nitro substitution, absent in other groups.
- Protic solvents enhanced ISC via intermolecular orbital mixing and additional transition channels.
Conclusions:
- Nitro substitution is an effective heavy-atom-free strategy for generating triplet states in organic molecules.
- Solvent polarity and hydrogen-bonding interactions play a critical role in modulating ISC rates and triplet yields.
- These findings offer insights for designing efficient organic materials for photonic applications through solvent-assisted doping.
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