Negatively photochromic organic compounds: Exploring the dark side

Gelombang mikro ialah gelombang elektromagnetik yang mempunyai kemampuan untuk proses pemanasan dalam 
menjalankan tindak balas kimia khususnya dalam sintesis sebatian heterosiklik. Penggunaan kaedah gelombang ini adalah 
salah satu alternatif untuk memperbaiki atau meningkatkan tahap kecekapan suatu tindak balas dengan mengurangkan 
masa tindak balas malah meningkatkan peratusan hasil yang diperoleh.

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Kaedah Gelombang Mikro: Alternatif Sintesis Sebatian Heterosiklik Konvensional

Comprehensive study of substituent effects on structure and photochromic properties of 1,3-benzoxazine-4-one spiropyrans

The corresponding merocyanins (II and III), which are not capable of intramolecular cyclization to form spiropyrans, were obtained by the condensation of quaternary salts of 2- and 4-methylquinoline with o-hydroxyaryl aldehydes. In contrast to II and III, the products of the condensation of 5, 6-dimethylphenanthridinium salts with o-hydroxyaryl aldehydes (IV and V) exist, under the usual conditions, in the spiropyran form, while the derivative of 5-nitrosali-cylaldehyde can be isolated in both the cyclic and merocyanin forms. These differences are associated with the magnitude of the positive charge on the carbon atom which participates in closing the pyran ring.

Spiropyrans based on nitrogen heterocycles

Synthesis and properties of spiropyrans capable of reversible opening of the pyran ring

1.

The photochemical opening of the ring of phenanthridine spiropyrans occurs through a singlet excited state in direct photolysis and through a triplet state in sensitized photolysis.




2.

At high concentrations of the colored form of spiropyrans, its molecules are capable of dimerization.




3.

Atmospheric oxygen accelerates the decolorization of the colored form.

Investigation of the photochrome properties of spiropyrans of the phenanthridine series by the method of pulsed photolysis

The relative stabilities of the cyclic and open forms of spiropyrans of the phenanthridine series depend on the character and position of the substituents in the chromene ring and also on the polarity of the media. The structure of the open forms of the spiropyrans is closer to the limiting dipolar structure. The open forms of the carboxy derivatives of the spiropyrans are stabilized in alcohol solutions due to proton transfer to the phenoxide oxygen.

L. S. Efros

Papers

Spiropyrans based on nitrogen heterocycles

Synthesis and properties of spiropyrans capable of reversible opening of the pyran ring

Investigation of the photochrome properties of spiropyrans of the phenanthridine series by the method of pulsed photolysis

Spiropyrans of the phenanthridine series