Highly Efficient Room-Temperature Phosphorescence from Halogen-Bonding-Assisted Doped Organic Crystals

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Metal-free organic room temperature phosphorescence (RTP) materials are crucial for advanced applications like sensors and anticounterfeiting.
• Achieving high RTP efficiency is challenging due to inefficient intersystem crossing (ISC) and competing nonradiative relaxation pathways.

Purpose of the Study:

• To develop a facile strategy for highly efficient metal-free organic RTP materials.
• To investigate the role of halogen bonding in enhancing RTP efficiency.

Main Methods:

• Doping iodo difluoroboron dibenzoylmethane (I-BF2dbm-R) derivatives into a rigid crystalline 4-iodobenzonitrile (Iph-C≡N) matrix.
• Utilizing halogen bonding (Iph-C≡N···I-BF2dbm-R) to suppress nonradiative relaxation and promote spin-orbit coupling (SOC).
• Systematically varying the substituent group R on the I-BF2dbm-R dopant to tune phosphorescence properties.

Main Results:

• The doped crystals exhibited intense RTP with an efficiency of up to 62.3%.
• Halogen bonding was identified as a key interaction suppressing nonradiative decay and enhancing SOC.
• Increasing the electron-accepting strength of the substituent R group significantly enhanced the phosphorescence-to-fluorescence intensity ratio.

Conclusions:

• A novel strategy using halogen bonding in doped crystals enables highly efficient metal-free organic RTP.
• The developed materials show significant promise for applications in sensing, imaging, and anticounterfeiting.
• Tuning molecular structure provides a pathway to optimize RTP performance.