Highly Strained, Radially π-Conjugated Porphyrinylene Nanohoops

Area of Science:

• Supramolecular Chemistry
• Organic Electronics
• Materials Science

Background:

• Small π-conjugated nanohoops are challenging to synthesize but valuable for studying strain effects.
• These macrocycles are increasingly used in host-guest chemistry and self-assembly applications.

Purpose of the Study:

• To report the synthesis of novel radially π-conjugated porphyrinylene/phenylene nanohoops.
• To investigate the impact of ring strain on optoelectronic and supramolecular properties.

Main Methods:

• Synthesis of porphyrinylene/phenylene nanohoops using a defined strategy.
• Characterization of strain energy, HOMO-LUMO gap, and absorption spectra.
• Host-guest binding studies with fullerenes (C60, C70) using X-ray crystallography.
• Computational analysis (DFT) to understand synthetic limitations.

Main Results:

• The smallest nanohoop [2]CPT exhibits significant strain energy (54 kcal mol⁻¹), leading to a narrowed HOMO-LUMO gap and red-shifted absorption.
• [2]CPT shows high binding affinity (>10⁸ M⁻¹) for C60.
• Extended π-systems ([2]CPTN, [3]CPTN, [3]CPTA) were synthesized; [2]CPTN binds C70 five times more strongly than [2]CPT.
• Failed synthesis of [2]CPTA highlights limitations of strain introduction methods.

Conclusions:

• Introducing ring strain into organic semiconductors is a viable strategy to tune optoelectronic and supramolecular properties.
• Strained nanohoops show promise for advanced host-guest chemistry and materials applications.