Supramolecular alternating copolymers with highly efficient fluorescence resonance energy transfer

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Polymer Chemistry

Background:

• Naphthalene-diimide (NDI) derivatives are explored for their unique photophysical properties.
• Controlled self-assembly of distinct molecular building blocks is crucial for designing functional materials.
• Supramolecular polymerization offers a pathway to ordered structures with tunable properties.

Purpose of the Study:

• To investigate the alternating supramolecular copolymerization of two distinct NDI monomers (NDI-1 and NDI-2).
• To elucidate the thermodynamic control and self-assembly behavior of these NDI derivatives.
• To explore the formation of ordered aggregates and their impact on photophysical properties like FRET.

Main Methods:

• Synthesis of NDI-1 and NDI-2 monomers with varying functional groups.
• UV/Vis spectroscopy and temperature-dependent studies to analyze aggregation and polymerization.
• Molecular dynamics simulations and theoretical calculations to predict intermolecular interactions and stacking.
• Job's plot analysis to determine copolymer stoichiometry.

Main Results:

• A 1:1 mixture of NDI-1 and NDI-2 spontaneously forms a fibrillar network and gels, unlike individual components.
• The mixed system exhibits J-aggregation in decane, indicated by sharp, bathochromically shifted absorption and emission bands with a small Stokes shift.
• Temperature-dependent studies reveal early nucleation and cooperative polymerization in the 1:1 mixture.
• Theoretical studies predict favorable alternating stacking due to partial charges and steric factors, confirmed by 1:1 stoichiometry.
• The resulting alternating supramolecular copolymers demonstrate highly efficient (>93%) fluorescence resonance energy transfer (FRET).

Conclusions:

• Alternating supramolecular copolymerization of NDI-1 and NDI-2 is achieved under thermodynamic control.
• The specific functionalization of NDI-2 promotes alternating stacking with NDI-1, leading to well-defined H-bonded supramolecular copolymers.
• These novel copolymers exhibit efficient FRET, highlighting their potential for applications in optoelectronics and sensing.