Electronic and vibrational exciton coupling in oxidized trianglimines

Area of Science:

• Chiroptical spectroscopy
• Supramolecular chemistry
• Computational chemistry

Background:

• Chiral macrocycles, specifically trianglimines, are valuable for studying exciton chirality methods.
• Polar substituents on macrocyclic skeletons significantly influence electronic and vibrational circular dichroism (ECD/VCD) spectra.

Purpose of the Study:

• To investigate the impact of polar substituents on the ECD and VCD spectra of chiral trianglimines.
• To evaluate the reliability of ECD and VCD exciton chirality interpretation for these macrocycles.
• To compare the chiroptical properties of trianglimines with their constituent diimines.

Main Methods:

• Synthesis of chiral trianglimines and their (poly)oxygenated derivatives.
• Measurement of electronic and vibrational circular dichroism (ECD/VCD) spectra.
• Density Functional Theory (DFT) calculations for spectral analysis.

Main Results:

• Hydroxyl group substitution reversed the exciton couplet sign in the UV absorption region.
• Methoxy group substitution resulted in two exciton couplets with differing signs in the ECD spectrum.
• Vibrational exciton couplets observed in VCD spectra of C=N stretches showed signs opposite to diamine chirality.
• Trianglimine VCD spectra provided more convincing exciton chirality interpretation than ECD spectra.
• Constituent diimines lacked observable vibrational exciton effects.

Conclusions:

• Trianglimine macrocycles are excellent models for testing and validating chiroptical methods.
• VCD spectroscopy offers a more robust interpretation of exciton chirality in these systems compared to ECD.
• DFT calculations provide accurate predictions, supporting experimental findings.