Hydroxypyridinechromene and pyridinechalcone: two coupled photochromic systems

Area of Science:

• Organic Chemistry
• Photochemistry
• Supramolecular Chemistry

Background:

• 2-hydroxychalcones are versatile organic compounds with diverse reaction pathways.
• The electronic and structural properties of chalcones influence their reactivity and photochemical behavior.
• Understanding reaction networks in solution is crucial for designing novel photoresponsive materials.

Purpose of the Study:

• To investigate the chemical reaction network of 2-hydroxychalcones substituted with a 4-pyridine unit.
• To characterize the formation, equilibrium, and kinetics of chalcone-type and hemiketal species.
• To explore the photoisomerization and photochromism within this novel compound system.

Main Methods:

• Synthesis and characterization of the 4-pyridine substituted 2-hydroxychalcone.
• (1)H NMR spectroscopy to analyze reaction equilibria and kinetics.
• UV/Vis spectrophotometry to monitor spectral changes and photochemical transformations.

Main Results:

• Substitution with a 4-pyridine unit led to the formation of trans-chalcone-type (Ct), cis-chalcone-type (Cc), and hemiketal (B) species, with no flavylium cation detected.
• Equilibria between Ct, Cc, and B occurred on a timescale four orders of magnitude slower than in analogous 2-phenyl-2-benzopyrylium compounds.
• Photoirradiation induced cis-trans isomerization (Ct <--> Cc) and photochromism (Ct/Cc <--> B) with distinct quantum yields.

Conclusions:

• The 4-pyridine substitution significantly alters the reaction network and kinetics of 2-hydroxychalcones.
• The compound exhibits complex photochemical behavior, including photoisomerization and photochromism.
• Detailed kinetic and equilibrium studies are feasible due to the slow timescale of these processes, enabling potential applications in photoresponsive systems.