Iron–Carbonyl Aqueous Vesicles (MCsomes) by Hydration of [Fe(CO){CO(CH₂)₅CH₃}(Cp)(PPh₃)] (FpC6): Highly Integrated Colloids with Aggregation‐Induced Self‐Enhanced IR Absorption (AI‐SEIRA)

Abstract

Self-assembly of hydrophobic molecules into aqueous colloids contradicts common chemical intuition, but has been achieved through hydration of [Fe(CO){CO(CH2)5CH3}(Cp)(PPh3)] (FpC6). FpC6 has no surface activity, no NMR signals in D2O and no critical aggregation concentration (CAC) in H2O. The molecule, however, contains both acyl and terminal CO groups that are prone to being hydrated. By adding water to a solution in THF, self-assembly of FpC6 can be initiated through water-carbonyl interactions (WCIs) with the highly polarized acyl CO groups. This aggregation subsequently enhances the hydration of the acyl CO groups and also induces the WCI of otherwise unhydrated terminal CO groups. The resultant metal-carbonyl aggregates have been proved to be bilayer vesicles with iron complexes exposed towards water and alkyl chains forming inner walls (MCsomes). These MCsomes show high structure integration upon dilution due to the hydrophobic nature of the building blocks. The highly polarized CO groups on the surface of the MCsomes result in a negative zeta potential (-65 mV) and create a local electric field, which significantly enhances the IR absorption of CO groups by more than 100-fold. This is the first discovery of aggregation-induced self-enhanced IR absorption (AI-SRIRA) without the assistant of external dielectric substrates. Highly integrated MCsomes are, therefore, promising as a novel group of materials, for example, for IR-based sensing and imaging.

Hierarchical Self‐Assembly Induced by Dilution‐Enhanced Hydrophobic Hydration

“…We have reported aqueous self‐assembly of hydrophobic molecules, FpX (Fp head=(PPh 3 )(Cp)Fe(CO)(CO‐); X=hydrocarbon tail) . FpX molecules are non‐surface active and not amphiphilic, but able to assemble in water into Metal Carbonyl bi‐layer vesicles (MCsome) . HH of the hydrophobic Fp heads is responsible for the dispersion of MCsomes in water .…”

“…FpX molecules are non‐surface active and not amphiphilic, but able to assemble in water into Metal Carbonyl bi‐layer vesicles (MCsome) . HH of the hydrophobic Fp heads is responsible for the dispersion of MCsomes in water . The zeta potentials (ζ) of MCsomes is negative due to the presence of water carbonyl interactions (WCIs) .…”

“…HH of the hydrophobic Fp heads is responsible for the dispersion of MCsomes in water . The zeta potentials (ζ) of MCsomes is negative due to the presence of water carbonyl interactions (WCIs) . It suggests that the carbonyl oxygen is partially negative charged (O[δ − ]) with its HH level relatively higher than the partially positive charged Fe (Fe[δ + ]) .…”

“…Fp(CH 2 ) 6 Azobenzene trans molecules are hydrophobic and non‐surface active (Figure S1), and can self‐assemble in water using THF as a common solvent (Figure S2 a) . Like FpX, Fp(CH 2 ) 6 Azobenzene trans assembles into MCsomes (140 μ m ) (Figure a and Figure S3) with detectable WCIs (Figure S2 b).…”

The Effect of Solution Conditions on the Driving Forces for Self‐Assembly of a Pyrene Molecule

“…Fp‐pyrene was prepared in a reaction between 1‐(6‐bromohexyl) pyrene and potassium cyclopentadienyldicarbonyliron (FpK), followed by a migration insertion reaction (MIR) in the presence of triphenylphosphine (Supporting Information, Scheme S1 and Figure S1) . The self‐assembly was first performed by injecting water into a DMSO solution of Fp‐pyrene, which resulted in the same concentrated solutions with various volume ratios of the two solvents.…”