Structure and photochromic properties of a single-crystalline spiro[indolinepyranopyridinium] salt

Abstract

The molecular and crystal structure of single crystalline 5´ hydroxymethyl 1,3,3,7´,8´ pentamethylspiro[indoline 2,2´ [2H ] pyrano[3,4 b]pyridinium] iodide (1) was studied. The crystal structure is composed of cation layers separated by iodide ions and provides a sufficient volume for the phototransformation of compound 1. The spectroscopic and photochromic properties of this compound in the crystalline state were investigated. Upon irradiation with light at 270-370 nm, up to 600 layers of single crystals are subjected to photochromic transfor mations. The quantum yield of formation of the open form is ~0.1, and the quantum yield of decoloration is 0.04. After ten reversible photocyclizations, the absorption of the colored form was decreased by 10%. The photochromic properties were related to the single crystal struc ture.Key words: spiropyran salt, spiro[indolinepyranopyridinium] iodide, single crystal, photo chromic properties.In recent years, solid state photochromic transforma tions of spiropyrans have attracted considerable interest not only from the viewpoint of the design of new materi als for optical information storage and processing 1,2 but also for the preparation of new polyfunctional materials combining different properties in a crystal lattice. 3,4 In these crystals, photoinduced transformations can give rise to new functions (for example, photoswitching of nonlin ear optical properties 5 ). However, photochromic trans formations in crystals of spiropyrans and spirooxazines are rather hindered due to the close packing of the mol ecules in the crystal lattice and also because these phototransformations, which are associated with the C spiro -O bond cleavage followed by isomerization of the molecule, require a large free volume. As a rule, spiro pyrans and spirooxazines in microcrystalline powders do not exhibit the photochromic properties under conditions of stationary irradiation. However, the use of intense femtosecond laser irradiation leads to the formation of a short lived photocolored form in microcrystals, whose absorption spectrum is identical to the spectra of the photo forms of spiropyran and spirooxazine in solutions. 6 Recently, pyridinium containing salts of spiropyrans and spirooxazines, which possess the photochromic prop erties in the crystalline state, have been synthesized. 3,7,8 Study of ultrathin pressed microcrystalline samples dem onstrated that they become colored under continuous UV irradiation. The constant of thermal decoloration of the resulting photo form (k) is 10 -4 -10 -8 s -1 . The unusual behavior of the crystals of spiropyrans and spirooxazines was attributed to the electron withdrawing effect of the positively charged N methylpyridinium ring and/or the characteristic features of the crystal packing of salts of spiropyran and spirooxazine. To correctly interpret the properties of these compounds, it is necessary to study the structures of their single crystals and photochromic trans formations occurring in the crystals.In the present study, we synthesized cationic sp...

Photo-and thermochromic properties of 1′,3′,3′-trimethyl-6-nitro-8-pyridiniomethylspiro[2H-[1]benzopyran-2,2′-indoline] chloride in the crystalline state

“…Such a structure should prevent the isomerization of MC forms of the molecules and formation of closed SP forms in crystals, as observed for spiropyrans in the non salt form, 7 unlike the salt forms. 5, 6 Spectral and photochemical properties. It has been shown that compound 1 synthesized previously 2 exhibits photochromic properties in solutions.…”

“…It has recently been shown 3,4 that the structure of the magnetic anionic sublattice of bimetallic oxalates [M III M II (ох) 3 ] -allows cation size variation to perform in a wide range, and the crystal structure of the spiropyran cation in salts with chloride and iodide anions is found to be favorable for reversible photochromic transformations of spiropyrans. 5, 6 These features of the structures of the cationic and anionic sublattices allowed crystal chemical modeling of photochromic ferromagnets to be per formed. 1,2 In this case, it was important that the SP + cation was involved in the reaction in the closed form.…”

Photochromic properties of phenanthroline-annulated spirooxazine in the solid state

“…As a rule, spiropyrans and spirooxazines are not photochemically active in microcrystalline pow ders and single crystals. 9 This is explained by the fact that the phototransformations caused by bond cleavage between the spiro carbon atom and oxygen atom followed by isomerization of the molecule require large free volume.…”

Photo- and thermochromic spiranes. 31.* Photochromic cationic spiropyrans with a pyridinium fragment in the aliphatic side chain*2

“…Salts of spiropyrans (SP + X -) and spirooxazines (SO + X -) hold promise for the development of hybrid polyfunctional materials, combining photochromic and magnetic properties in a single crystal lattice [6][7][8][9]16], in which the spiropyran or spirooxazine cations have photochromic properties. Thus, the synthesis, structure, and photochemical properties of cationic spiropyrans and spirooxazines have recently attracted considerable investigation [8,9,[14][15][16][17]. A completely new class of hybrid polyfunctional compounds has recently been discovered.…”