Hexa-Branched Nanographenes with Large Two-Photon Absorption.

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Conventional strategies for high two-photon absorption (TPA) rely on donor-acceptor molecular structures.
• Exploring alternative molecular architectures is crucial for advancing TPA materials.

Purpose of the Study:

• To investigate hexa-branched nanographenes as a novel platform for achieving large TPA.
• To demonstrate that TPA efficiency can be enhanced through molecular topology rather than solely relying on donor-acceptor designs.

Main Methods:

• Synthesis of two distinct hexa-branched nanographenes: one with benzoaceanthrylene arms and another with pyrenyl arms, both fused to a coronene core.
• Measurement of two-photon absorption (TPA) cross-sections for the synthesized nanographenes.
• Theoretical analysis to elucidate the relationship between molecular structure and TPA properties.

Main Results:

• The synthesized hexa-branched nanographenes exhibited significant TPA values (3.6 × 10³ and 1.9 × 10⁴ GM).
• These values represent the highest TPA cross-sections recorded for heteroatom-free hydrocarbon molecules to date.
• The study found no requirement for a donor-acceptor structure to achieve high TPA.

Conclusions:

• Molecular topology and fused conjugated skeleton design are critical factors for achieving large TPA cross-sections.
• Hexa-branched nanographenes offer a promising alternative structural motif for developing materials with enhanced TPA properties.
• This work expands the design principles for high-performance TPA molecules beyond traditional donor-acceptor approaches.