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T 1/2 Tuning in a Synergistic BODIPY-Tetrazole Fe(II) Spin Crossover-Photoluminescence System via Counterion
Martin Huber1, Matthias Schöbinger1, Berthold Stöger2
1Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9, 1060 Vienna, Austria.
Crystal Growth & Design
|November 10, 2025
Summary
Researchers developed new spin crossover (SCO) materials by combining them with photoluminescence (PL). They found that counteranion size influences SCO abruptness, enabling tunable molecular sensors.
Area of Science:
- Coordination Chemistry
- Materials Science
- Molecular Electronics
Background:
- Spin crossover (SCO) materials offer bistability for molecular sensors.
- Integrating SCO with photoluminescence (PL) is challenging but promising.
- Tuning SCO properties while maintaining PL is key for advanced applications.
Purpose of the Study:
- Synthesize novel heteroleptic Fe(II) coordination compounds with a BODIPY-tetrazole ligand.
- Investigate the effect of counteranion size and coordination on SCO and PL properties.
- Establish a platform for independent tuning of SCO and PL for multifunctional devices.
Main Methods:
- Synthesis of Fe(II) coordination compounds with varying counteranions (BF4-, ClO4-, PF6-, CF3SO3-, SbF6-).
- Magnetic susceptibility measurements to study spin crossover transitions.
- Spectroscopic analysis to correlate SCO with photoluminescence changes.
Main Results:
- Counteranion size impacts SCO transition abruptness and completeness.
- The BF4- complex shows the most abrupt SCO with synergistic SCO-PL modulation.
- CF3SO3- coordination to Fe(II) leads to a phase transition, not SCO.
- Coordination of CF3SO3- is reversible via topochemical exchange with water.
Conclusions:
- Counteranion engineering provides a route to tune SCO behavior in Fe(II) complexes.
- Electronic coupling between SCO and PL is observed in specific complexes.
- The developed system offers independent control over SCO and PL properties for sensor applications.
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