Scientific journal

European Journal of Natural History

ISSN 2073-4972

ИФ РИНЦ = 0.204

NOVEL PHOTOCHROMIC SPIROPYRANS DERIVED FROM 6-HYDROXY-4-METHYL-5-FORMYLCOUMARIN

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Dubonosov A.D., Nikolaeva O.G., Tsukanov A.V.

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Novel indoline, isobenzofuran and naphtopyran spiropyrans (SPPs) containing in 2H-chromene part of the molecules fused coumarin moiety were synthesized. According to 1H NMR, IR and UV/Vis spectral data these compounds exist in cyclic spiroform SP. Under irradiation of their solutions in isopentane-isopropanole (4:1) mixture at Т < 250 К the formation of merocyanine (MC) isomer was observed. The back reaction MC ® SP is thermally reversible.

hotochromic spiropyrans (SPPs) are widely used for data recording, as photocontrolled organic molecular switches, in devices of molecular electronics and as chemosensors for metal cations [1-4]. Some representatives of coumarin-containing SPPs were synthesized earlier [5-9]. In order to study influence of annelation manner of coumarin moiety to 2H-chromene part of the molecule on photochromic and spectral properties of SPPs novel indoline, isobenzofuran and naphtopyran spiropyrans were synthesized.

6-Hydroxy-4-methyl-5-formylcoumarin 1 as aldehyde component was used for the synthesis of above mentioned SPPs. Perchlorates of N-substituted 3H-indolium, isobenzofuranium and benzo[f]chromenium were employed to form hetaryl part of the molecules. Spiropyrans 2 were obtained by condensation of corresponding 3H-indolium perchlorates with aldehyde 1 in isopropanol in the presence of triethylamine
(scheme 1).

Spiropyrans 3,4 were synthesized in two steps (scheme 2). The first one represented condensation of isobenzofuranium and benzo[f]chromenium perchlorates with aldehyde 1 in acetic acid. The second step consisted in treatment of intermediate product by dry ammonia in benzene
solution.

In upfield region of ¹H NMR spectra of spiropyrans 2-4 are present two signals of magnetic unequivalent gem-methyl groups. Signals of diastereotopic methylen group protons of N-benzyl substituent in SPP 2a are observed as two doublets at 4,20-4,30 ppm. Signal of Н-2 proton in double bond of pyran cycle of compounds 2-4 are registered as doublet at
5,32-5,85 ppm. Doublet of Н-1 proton is closed by aromatic proton signals at 7,00-8,50 ppm. However for molecules 2b,c,d and 4 this doublet is seen at 7,40-7,60 ppm. These data confirm that SPPs 2-4 exist in cyclic SP form.

Singlet signal of Н-9 proton in coumarin moiety is registered in the region 6,15-6,19 ppm. The location of Н-5 and Н-6 protons is very specific: doublet at 6,56-6,90 ppm. The second doublet of these protons is closed by aromatic proton signals at 7,00-8,50 ppm, however for 2d it is seen at 7,32-7,36 ppm.

Notes:

* Signal of the second proton is in the region of aromatic proton signals;

Electronic absorption spectra of SPPs 2-4 in isopentane-isopropanol mixture (4:1) show long-wavelength bands with maxima centered around 364-402 nm with strongly marked vibration structure which are indicative for cyclic forms SP [2, 10, 11]. The irradiation of compounds 2-4 SP in above mentioned solution (λ_irr 365 nm, Т < 250 К) leads to formation of merocyanine isomers 2-4 MC. In dark conditions these isomers thermally convert into the initial spiroforms
(table 2).

According to these data a new type of photochromic coumarin-containing SPPs was synthesized.

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