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Unlocking the Room Temperature Phosphorescence through Halogen Engineering in Carbazole Dimer
Jibin Sivanarayanan1, Kavya Vinod1, Anitta Benoy1
1School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Maruthamala-P. O., Vithura, Thiruvananthapuram, 695551, India.
Researchers developed metal-free organic materials for room-temperature phosphorescence (RTP). Bromine substitution in carbazole dimers enhanced spin-orbit coupling and facilitated RTP through halogen bonding in crystals.
Area of Science:
- Materials Science
- Organic Chemistry
- Photophysics
Background:
- Room-temperature phosphorescence (RTP) in metal-free organic materials is crucial for optoelectronics.
- Designing and controlling RTP is challenging due to complex structure-photophysics relationships.
Purpose of the Study:
- To investigate the role of intersystem crossing (ISC), spin-orbit coupling (SOC), and halogen interactions in promoting RTP.
- To explore the structure-property correlations for developing efficient organic phosphorescent materials.
Main Methods:
- Synthesis of brominated carbazole dimer (BrCz-D) and unsubstituted carbazole dimer (Cz-D).
- Femtosecond transient absorption (fsTA) spectroscopy to confirm triplet state population.
- Crystallographic analysis to identify halogen interactions.
Main Results:
- Bromine substitution significantly enhanced spin-orbit coupling (VSOC = 14.94 cm⁻¹) in BrCz-D, promoting efficient ISC and RTP.
- BrCz-D exhibited robust RTP in crystalline form, attributed to intermolecular halogen interactions (Br···Br, C···Br, H···Br).
- The unsubstituted Cz-D showed thermally activated delayed fluorescence (TADF) and lacked RTP in solution due to negligible halogen interactions.
Conclusions:
- SOC and halogen bonding are critical for achieving efficient RTP in organic materials.
- Crystallochemistry and strategic halogenation are effective strategies for designing high-performance organic phosphorescent materials.
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