Porphyrazine
Encyclopedia
Porphyrazines, or tetraazaporphyrins, are tetrapyrrole
macrocycles similar to porphyrins and phthalocyanines
. Pioneered by Sir R. Patrick Linstead
as an extenstion of his work on phthalocyanines, porphyrazines differ from porphyrins in that they contain -meso nitrogen atoms, rather than carbon atoms, and differ from phthalocyanines in that their β-pyrrole positions are open for substitution. These differences confer physical properties that are distinct from both porphyrins and phthalocyanines.
or diiminoisoindole derivatives is possible introducing a flexibile synthetic route that has led to the synthesis of porphyrazines with peripheral heterocyclic rings, heteroatom
substituents (S, O, N),, peripherally bound metal atoms, and mixed -benzo porphyrazine systems.
, and NIR spectral regions. Electronic absorption spectra for porphyrazines are similar to those of phthalocyanines, with an intense Soret band (λ ≈ 300 - 400 nm) and Q-band (λ > 600 nm).
Porphyrazines exhibit fluorescence
from the first excited singlet state (S1 → S0) at visible and NIR wavelengths which is typical of tetrapyrrole macrocycles. Dual-emission from organic fluorophores is not common
but, as observed in phthalocyanines, violet emission from an upper excited state (S2 → S0) is observed in porphyrazines.
Tetrapyrrole
Tetrapyrroles are compounds containing four pyrrole rings. With the exception of corrin, the four pyrrole rings are interconnected through one-carbon bridges, in either a linear or a cyclic fashion...
macrocycles similar to porphyrins and phthalocyanines
Phthalocyanine
Phthalocyanine is an intensely blue-green coloured macrocyclic compound that is widely used in dyeing. Phthalocyanines form coordination complexes with most elements of the periodic table...
. Pioneered by Sir R. Patrick Linstead
Patrick Linstead
Sir Patrick Linstead CBE, DSc, HonDSc, DIC, HonFCGI, HonMIMM, FRS was an English chemist.-Career:...
as an extenstion of his work on phthalocyanines, porphyrazines differ from porphyrins in that they contain -meso nitrogen atoms, rather than carbon atoms, and differ from phthalocyanines in that their β-pyrrole positions are open for substitution. These differences confer physical properties that are distinct from both porphyrins and phthalocyanines.
Synthesis
Porphyrazines are prepared by magnesium templated cyclization of maleonitriles. Cross-cyclization with phthalonitrilePhthalonitrile
Phthalonitrile is an organic compound with the formula C6H42, which is an off-white crystal solid at room temperature. It is a benzene derivative, containing two adjacent nitrile groups. The compound is partially soluble in water, and is soluble in acetone, nitrobenzene, and benzonitrile...
or diiminoisoindole derivatives is possible introducing a flexibile synthetic route that has led to the synthesis of porphyrazines with peripheral heterocyclic rings, heteroatom
Heteroatom
In organic chemistry, a heteroatom is any atom that is not carbon or hydrogen. Usually, the term is used to indicate that non-carbon atoms have replaced carbon in the backbone of the molecular structure...
substituents (S, O, N),, peripherally bound metal atoms, and mixed -benzo porphyrazine systems.
Optical properties
Porphyrazines are most well known for their intense electronic absorption throughout the UV, visibleVisible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
, and NIR spectral regions. Electronic absorption spectra for porphyrazines are similar to those of phthalocyanines, with an intense Soret band (λ ≈ 300 - 400 nm) and Q-band (λ > 600 nm).
Porphyrazines exhibit fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
from the first excited singlet state (S1 → S0) at visible and NIR wavelengths which is typical of tetrapyrrole macrocycles. Dual-emission from organic fluorophores is not common
Kasha's rule
Kasha's rule is a principle in the photochemistry of electronically excited molecules. The rule states that photon emission occurs in appreciable yield only from the lowest excited state of a given multiplicity...
but, as observed in phthalocyanines, violet emission from an upper excited state (S2 → S0) is observed in porphyrazines.