Anion-π and cation-π interactions on the same surface.

Area of Science:

• Supramolecular Chemistry
• Photophysics
• Organic Electronics

Background:

• Aromatic systems are known to engage in anion-π and cation-π interactions independently.
• Understanding simultaneous interactions is crucial for designing advanced functional materials.
• Push-pull chromophores offer a unique platform due to their inherent dipole moments.

Purpose of the Study:

• To investigate the simultaneous occurrence of anion-π and cation-π interactions on the same aromatic surface.
• To explore push-pull chromophores as platforms for "ion pair-π" interactions.
• To quantify the influence of these interactions on photophysical properties.

Main Methods:

• Synthesis of 4-amino-1,8-naphthalimides functionalized with carboxylate-guanidinium pairs.
• Spectroscopic analysis (UV-Vis absorption and emission) in various solvents.
• Theoretical calculations (DFT) to model ground and excited states.

Main Results:

• Observation of a significant bathochromic shift (red shift) in antiparallel ion pair-π orientation.
• Experimental red shift of 41 nm in non-polar solvent, aligning with theoretical predictions of 70 nm.
• Intramolecular Stark effect from antiparallel interactions dominates over solvatochromic effects.
• Theoretical evidence for interactions with π-acidic (naphthalenediimides) and π-basic (pyrenes) surfaces.

Conclusions:

• Push-pull chromophores are effective platforms for simultaneous anion-π and cation-π interactions.
• Antiparallel ion pair-π interactions induce substantial electronic changes, particularly a bathochromic shift.
• These interactions offer a powerful tool for tuning chromophore properties, with potential applications in molecular electronics and sensing.