A Magnetically Bistable Rigid Carbene─2,3-Benzofluorenylidene

Area of Science:

• Organic Chemistry
• Physical Chemistry
• Quantum Chemistry

Background:

• Spin-crossover (SCO) phenomena are typically observed in metal-containing compounds.
• Organic molecules exhibiting bistable spin states are exceptionally rare.
• Understanding SCO in metal-free systems is crucial for novel material design.

Purpose of the Study:

• To synthesize and characterize a spin-bistable organic carbene, 2,3-benzofluorenylidene.
• To investigate the influence of inert matrices on the spin state population.
• To explore the spin-selective reactivity of the singlet (S) and triplet (T) states.

Main Methods:

• Cryogenic synthesis and isolation of 2,3-benzofluorenylidene in inert matrices (Ne, Ar, Xe, N2).
• Spectroscopic analysis to determine the S/T spin state ratio.
• Ab initio calculations to model spin-selective solvation effects.
• Reactivity studies with small molecules (H2, D2, H2O, O2, CO).

Main Results:

• 2,3-benzofluorenylidene exists as a mixture of singlet and triplet states at cryogenic temperatures.
• The S/T ratio is strongly dependent on the inert matrix environment (e.g., T favored in Ar/Xe, S in Ne/N2).
• Matrix effects on the spin-state population are attributed to spin-selective solvation influencing intersystem crossing (ISC).
• Distinct reactivity patterns were observed for the S and T states toward various small molecules, demonstrating spin-selective chemical behavior.

Conclusions:

• The synthesized 2,3-benzofluorenylidene exhibits robust spin bistability in metal-free organic systems.
• Spin-selective solvation effects in inert matrices control the spin state population.
• The study highlights the potential for exploiting spin-selective reactivity in organic molecules for chemical applications.