09-25-2021-1518 - Internal conversion

Internal conversion is a transition from a higher to a lower electronic state in a molecule or atom.^[1] It is sometimes called "radiationless de-excitation", because no photons are emitted. It differs from intersystem crossing in that, while both are radiationless methods of de-excitation, the molecular spin state for internal conversion remains the same, whereas it changes for intersystem crossing. The energy of the electronically excited state is given off to vibrational modes of the molecule. The excitation energy is transformed into heat.

Jablonski diagram indicating intersystem crossing (left) and internal conversion (right).

Examples[edit]

A classic example of this process is the quinine sulfate fluorescence, which can be quenched by the use of various halide salts.^{[citation needed]} The excited molecule can de-excite by increasing the thermal energy of the surrounding solvated ions.

Several natural molecules perform a fast internal conversion. This ability to transform the excitation energy of photon into heat can be a crucial property for photoprotectionby molecules such as melanin.^[2] Fast internal conversion reduces the excited state lifetime, and thereby prevents bimolecular reactions. Bimolecular electron transfer always produces a reactive chemical species, free radicals.^{[citation needed]} Nucleic acids (precisely the single, free nucleotides, not those bound in a DNA/RNA strand) have an extremely short lifetime due to a fast internal conversion.^[3]

Both melanin and DNA have some of the fastest internal conversion rates.^{[citation needed]}

In applications that make use of bimolecular electron transfer the internal conversion is undesirable. For example, it is advantageous to have a long lived excited states in Grätzel cells (Dye-sensitized solar cells).

https://en.wikipedia.org/wiki/Internal_conversion_(chemistry)

https://en.wikipedia.org/wiki/Emission_spectrum

https://en.wikipedia.org/wiki/Atomic_emission_spectroscopy

https://en.wikipedia.org/wiki/Atomic_orbital

https://en.wikipedia.org/wiki/Atomic_electron_transition

https://en.wikipedia.org/wiki/Electromagnetic_radiation

https://en.wikipedia.org/wiki/Valence_electron#Valence_shell

https://en.wikipedia.org/wiki/Valence_bond_theory

https://en.wikipedia.org/wiki/Electron_shell

https://en.wikipedia.org/wiki/Electron_configuration#Noble_gas_configuration

https://en.wikipedia.org/wiki/Ionization

https://en.wikipedia.org/wiki/Excited_state#Atomic_excitation

https://en.wikipedia.org/wiki/Hydrogen_atom

https://en.wikipedia.org/wiki/Boltzmann_distribution

https://en.wikipedia.org/wiki/Two-dimensional_gas

https://en.wikipedia.org/wiki/Rydberg_atom

https://en.wikipedia.org/wiki/Quantum_number

https://en.wikipedia.org/wiki/Spectral_line

https://en.wikipedia.org/wiki/Continuous_spectrum

https://en.wikipedia.org/wiki/Ground_state

https://en.wikipedia.org/wiki/node

https://en.wikipedia.org/wiki/Chemical_bond

https://en.wikipedia.org/wiki/Periodic_table

https://en.wikipedia.org/wiki/Wave_function

https://en.wikipedia.org/wiki/Observable

https://en.wikipedia.org/wiki/Lewis_structure

https://en.wikipedia.org/wiki/model

https://en.wikipedia.org/wiki/Schrödinger_equation

https://en.wikipedia.org/wiki/numerical_model

https://en.wikipedia.org/wiki/Orbital_hybridisation

https://en.wikipedia.org/wiki/Resonance_(chemistry)

https://en.wikipedia.org/wiki/Atomic_orbital

https://en.wikipedia.org/wiki/Probability

https://en.wikipedia.org/wiki/Orbital_hybridisation

https://en.wikipedia.org/wiki/Molecular_orbital

https://en.wikipedia.org/wiki/Modern_valence_bond_theory

https://en.wikipedia.org/wiki/Core_electron

https://en.wikipedia.org/wiki/Valence_electron

https://en.wikipedia.org/wiki/Valence_electron#Electron_configuration

https://en.wikipedia.org/wiki/Chemical_element

https://en.wikipedia.org/wiki/Chemistry

https://en.wikipedia.org/wiki/Covalent_bond

https://en.wikipedia.org/wiki/Electron