Hydrogen-bonding-induced phenomena in bifunctional heteroazaaromatics

Area of Science:

• Photochemistry
• Supramolecular Chemistry
• Organic Chemistry

Background:

• Heterocyclic compounds with proton donor and acceptor sites are key for studying hydrogen bonding.
• Hydrogen bond formation significantly influences molecular electronic states and reactivity.
• Understanding excited-state dynamics is crucial for molecular design and function.

Purpose of the Study:

• To investigate ground and excited state processes in heterocyclic compounds induced by hydrogen bond formation.
• To elucidate the mechanisms of excited-state double proton transfer and internal conversion.
• To explore the role of molecular structure and environment in these photochemical reactions.

Main Methods:

• Spectroscopic analysis of heterocyclic compounds capable of forming hydrogen bonds.
• Investigation of photophysical properties in various solvent environments.
• Characterization of excited-state dynamics, including proton transfer and internal conversion.

Main Results:

• Excited-state double proton transfer and rapid S(0) <-- S(1) internal conversion observed in cyclic, multiply hydrogen-bonded complexes.
• Phototautomerization occurs in 1:1 cyclic, doubly hydrogen-bonded solvates, even in rigid solvents at low temperatures.
• Fluorescence quenching via photoinduced electron transfer detected with aromatic hydrogen-bonded acceptors like pyridine.
• Syn-anti rotamerization observed in molecules with linked proton donor and acceptor units due to hydrogen bonding.

Conclusions:

• Cyclic hydrogen-bonded complexes are essential for observing excited-state double proton transfer and internal conversion.
• Solvent rearrangement is critical for internal conversion, limiting it in rigid environments.
• Photoinduced electron transfer and rotamerization are additional hydrogen-bonding-induced processes affecting molecular behavior.