CHIRAL PURIFICATION OF IRIDIUM (III) COMPLEXES BY SFC

Importance of the Topic

Chiral iridium(III) complexes are key phosphorescent materials employed in OLED devices and as intracellular fluorescent probes. Their enantiomers exhibit distinct photophysical behaviors that directly influence device efficiency and biological imaging performance. Efficient separation of these stereoisomers is therefore critical for optimizing functional properties and ensuring reproducible results in research and industry.

Study Objectives and Overview

• Demonstrate supercritical fluid chromatography (SFC) for enantiomeric purification of two iridium(III) complexes: Flrpic and Ir(ppy)3.
• Optimize analytical-scale separation conditions on the Waters ACQUITY UPC2 System.
• Scale up the optimized methods to preparative purification using the Waters Prep SFC 150 Mgm System.
• Evaluate fraction recovery and enantiomeric purity following stacked injections.

Methodology

The study began with screening of co-solvents (acetonitrile and isopropanol) and gradient conditions to achieve baseline resolution of the two complexes on a 4.6×150 mm Chiralpak IA column. Isocratic elution parameters were then calculated to support stacked injections. Injection volumes were scaled from 2 µL to 20 µL for analytical studies, and further to 420–500 µL for preparative runs. CO₂ flow rates were converted from volumetric to mass flow for method transfer to the Prep SFC system. Recovery calculations were based on comparison of peak areas between collected fractions and standards.

Used Instrumentation

• Waters ACQUITY UPC2 System: 4.6×150 mm and 21×150 mm Chiralpak IA columns, PDA detection at 251 nm.
• Waters Prep SFC 150 Mgm System: 21×150 mm Chiralpak IA column, modifier‐stream injection mode.
• MassLynx 4.1 and ChromScope 2.0 software for data acquisition and method control.

Results and Discussion

• Optimal isocratic conditions were 30 % of 50:50 acetonitrile:isopropanol for Flrpic and 38 % isopropanol for Ir(ppy)3 at 40 °C and 124 bar.
• Analytical separation achieved complete enantiomeric resolution with retention times around 3.5–4.5 min.
• Preparative scaling maintained resolution using 60 mL/min CO₂ flow with matching co-solvent ratios and achieved clear peak shapes in stacked injections.
• Flrpic recoveries were 95 % and 97 % for enantiomeric fractions; Ir(ppy)3 recoveries were 87 % and 89 %, with minor loss attributed to solubility limits and transfer steps.
• No impurities were detected in Flrpic fractions; a ~1.5 % cross‐contamination was noted in one Ir(ppy)3 fraction.

Benefits and Practical Applications

• SFC offers faster run times, reduced solvent usage, and high throughput compared to traditional chiral HPLC.
• Scalable method enables preparative purification of enantiopure iridium complexes for OLED fabrication and bioimaging probes.
• High recovery and purity support consistent performance in device and biological applications.

Future Trends and Opportunities

• Integration of automated fraction collection with real‐time purity assessment.
• Expansion of chiral SFC to other transition‐metal complexes with challenging stereochemistry.
• Development of greener co‐solvent systems and alternative chiral stationary phases for improved selectivity.

Conclusion

SFC on Waters UPC2 and Prep SFC platforms provides a robust, scalable approach for the chiral separation and purification of iridium(III) complexes. The optimized isocratic methods delivered high enantiomeric resolution and recovery, demonstrating SFC's suitability for both analytical and preparative applications in materials science and chemical biology.

References

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5. Runco J., Aubin A. Chromatography Today, 11(3) (2018) 18–20