"Impurity"-driven tunable organic room temperature phosphorescence via conformational regulation in multi host/guest...

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Trace impurities significantly impact organic room temperature phosphorescent (ORTP) material properties.
• Biphenyl carboxylic acids (BCA) and biphenyl-4,4'-dicarboxylic acids (BDCA) were synthesized via Friedel-Crafts and cross-coupling routes.

Purpose of the Study:

• To investigate the cause of unexpected orange phosphorescence in Friedel-Crafts synthesized BCA and BDCA.
• To explore the potential of trace impurities as activators for tunable ORTP materials.

Main Methods:

• Comparative photoluminescence spectroscopy of synthesized BCA and BDCA.
• Identification of impurities using analytical techniques.
• Fabrication and characterization of bicomponent solids with controlled doping.
• Theoretical calculations to understand photophysical mechanisms.

Main Results:

• Friedel-Crafts synthesized materials exhibited orange phosphorescence, absent in cross-coupling products.
• Diphenylbenzil (DPB) impurities (<0.3 mol%) were identified as the RTP activators.
• Doping DPB into organic matrices yielded tunable RTP (green to red) with high quantum yield (26.4%) and long lifetime (1.6 ms).
• Photoexcited conformational dynamics of DPB and energy transfer channels (SSET, TTET) were elucidated.

Conclusions:

• Trace DPB doping is a novel strategy for developing tunable ORTP materials by controlling guest molecule geometry.
• Stabilizing specific DPB conformers in host matrices enhances quantum yield.
• Unusual RTP in commercial BDCA likely stems from DPB impurities, highlighting the need for careful system analysis.