Spiropyrans and spirooxazines represent an important class of photochromic compounds with a wide variety of applications. In order to effectively utilize and design these photoswitches it is desirable to understand how the substituents affect photochromic properties, and how the different structural motifs compare under identical conditions. In this work a small library of photoswitches was synthesized in order to comparatively evaluate the effect of substituent modifications and structure on photochromism. The library was designed to modify positions that were believed to have the greatest effect on C–O bond lability and therefore the photochromic properties. Herein we report a comparative analysis of the UV and visible light responses of 30 spiropyrans, spiroindolinonaphthopyrans, and spirooxazines. The influence of gadolinium(III) binding was also investigated on the library of compounds to determine its effect on photoswitching. Both assays demonstrated different trends in substituent and structural r...

Comparative Evaluation of Substituent Effect on the Photochromic Properties of Spiropyrans and Spirooxazines.

In this research a new method for preparing Mn(III)-salen complexes from 1,3-oxazine compounds has been investigated. The ligands were synthesized from the Mannich condensation of 1,2-diamines (1,2-ethylenediamine or 1,2-cyclohexanediamine) with phenolic compounds (2-naphthol or 4-flourophenol) and formaldehyde solution under reflux conditions. The reaction of the ligands with Mn(NO3)2·4H2O in methanol gave Mn(III) Schiff base complexes. The obtained compounds were characterized by elemental analysis and spectroscopic methods. The crystal structures of the ligand and complexes were characterized by single crystal X-ray diffraction studies. These analyses show that Mn(III)-salen type Schiff base complexes can be synthesized from the Mannich condensation of diamines, formaldehyde and phenols. This method eliminates the restrictions on the use of ortho-hydroxyaldehydes in preparing Mn(III)-Schiff base complexes.

Preparing Mn(III) salen-type Schiff base complexes using 1,3-oxazines obtained by Mannich condensation: towards removing ortho-hydroxyaldehydes

Photochromic Behavior and Diastereomeric Isomerism in [(η6-spirobenzopyran)RuCp*]PF6

Eleven new tetrahydrobenzo[b]pyran derivatives were synthesized via a three component reaction of different aromatic aldehydes, methyl cyanoacetate and 1,3-cyclohexadione, with water as solvent under catalyst-free microwave irradiation. The structures of all the new molecules were well analysed and their structures established by using various spectral techniques (1H NMR, 13C NMR, 15N NMR and HRMS). Various advantages of reported protocol are the ease of preparation, short reaction times (10 min), aqueous solvent and excellent yields (89–98%). Additionally, this method provides a clean access to the desired products by simple workup.

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A facile and one-pot synthesis of new tetrahydrobenzo[b]pyrans in water under microwave irradiation.

In this work, we present an innovative approach to stabilise the open-ring merocyanine form of a spiropyran compound. In the solid state, the merocyanine form is rarely observed, highlighting the importance of this contribution. Our concept is based on a co-crystallisation approach of the open form with an inorganic acid. This way, we identified a reliable technique for stabilising the coloured merocyanine form, and in one specific case, we even obtained crystals with increased stability towards photodegradation. 15 novel crystal structures of spiropyran derivatives with several inorganic acids were determined by single crystal X-ray diffraction. Solvent evaporation of spiropyran compounds, i.e. 1,3,3-trimethylindolinobenzopyrylospiran (SPH), 1,3,3-trimethylindolino-β-naphthopyrylospiran (SPBenz), 1,3,3-trimethylindolino-8′-methoxybenzopyrylospiran (SPOMe) and 1,3,3-trimethylindolino-6′-nitrobenzopyrylospiran (SPNO2), in the presence of inorganic acids, namely hydrochloric acid, hydrobromic acid, nitric acid, sulphuric acid and phosphoric acid, yielded the rare open-ring merocyanine form stabilised by protonation of the primary oxygen atom unfolded by ring-opening isomerisation and compensating the charge with a hydrogen bonded anion. Analysis of the solid state properties was performed by thermal gravimetric analysis and diffuse reflectance spectroscopy.

Acidochromic spiropyran–merocyanine stabilisation in the solid state

Spirobipyridopyrans, spirobinaphthopyrans, indolinospiropyridopyrans, indolinospironaphthopyrans and indolinospironaphtho-1,4-oxazines: synthesis, study of X-ray crystal structure, antitumoral and antiviral evaluation.

Linda Tomašković

Papers

Spirobipyridopyrans, spirobinaphthopyrans, indolinospiropyridopyrans, indolinospironaphthopyrans and indolinospironaphtho-1,4-oxazines: synthesis, study of X-ray crystal structure, antitumoral and antiviral evaluation.