Photoisomerization of "Partially Embedded Dihydropyridazine" with a Helical Structure

Area of Science:

• Organic Chemistry
• Photochemistry
• Materials Science

Background:

• Helicenes are chiral aromatic compounds with unique electronic and optical properties.
• Photochromic molecules can reversibly change color upon light irradiation.
• Biradicals are species with two unpaired electrons, often exhibiting unique magnetic properties.

Purpose of the Study:

• To synthesize novel partially embedded fused-dihydropyridazine N-aryl aza[5]helicene derivatives (PDHs).
• To investigate the photo-triggered multi-functional properties of these PDHs.
• To explore the potential for chirality control using photoracemization.

Main Methods:

• Synthesis of PDH-CF3 and PDH-C2F5 derivatives.
• Electron Spin Resonance (ESR) spectroscopy to detect biradical formation.
• Photo-irradiation studies in frozen solutions.
• Analysis of photochromic and thermally induced behaviors.

Main Results:

• PDHs exhibit axial chirality stable at room temperature.
• Photo-irradiation induces N-N bond dissociation, forming a triplet biradical.
• The system shows two equilibria: biradical/quinoidal and bond cleavage/recombination.
• T-type photochromism and photoracemization were observed.

Conclusions:

• The "partially embedded dihydropyridazine" structure is key to the observed functionalities.
• PDHs are promising candidates for photochromic materials and chirality control applications.
• The study demonstrates a novel mechanism for photoisomerization and biradical formation.