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Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
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The Electronic Structures of Azaphenanthrenes and Their Dimers
F Sturm1, L N Philipp1, M Flock1
1Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, Würzburg D-97074, Germany.
The Journal of Physical Chemistry. A
|February 12, 2024
Summary
Introducing nitrogen into polycyclic aromatic hydrocarbons (PAHs) alters their electronic structure and photochemistry. This study investigates azaphenanthrenes, revealing how nitrogen
Area of Science:
- Photochemistry
- Quantum Chemistry
- Spectroscopy
Background:
- Polycyclic aromatic hydrocarbons (PAHs) are fundamental molecules with diverse applications.
- Incorporating nitrogen atoms into PAHs creates polycyclic aromatic nitrogen-containing hydrocarbons (PANHs), altering their electronic and photochemical properties.
- The position of the nitrogen atom significantly influences the electronic structure and excited states of PANHs.
Purpose of the Study:
- To investigate the electronic structures of isolated PANH monomers and dimers.
- To understand the influence of nitrogen atom position on electronic properties and photochemistry.
- To characterize the excited electronic states of azaphenanthrenes using experimental and computational methods.
Main Methods:
- Resonance-enhanced multiphoton ionization (REMPI) spectroscopy for experimental characterization of excited states.
- Density functional theory (DFT) computations for theoretical analysis.
- Time-independent approach for simulating vibrationally resolved spectra.
Main Results:
- Azaphenanthrene monomers exhibit similar REMPI spectra with 1ππ* ← S0 transitions between 3.645 and 3.670 eV.
- The 2ππ* ← S0 transition in azaphenanthrenes is broad and unstructured, unlike in phenanthrene.
- Low-lying 1(nπ*) states in azaphenanthrenes accelerate nonradiative deactivation.
- Spectra of PANH dimers show overlapping bands from two π-stacked isomers, complicating assignments.
Conclusions:
- The presence of a low-lying 1(nπ*) state significantly perturbs the electronic structure of azaphenanthrenes compared to phenanthrene.
- This perturbation leads to accelerated nonradiative decay pathways.
- The electronic spectra of PANH dimers are complex due to contributions from multiple π-stacked isomers.
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