Cations of Photochromic Spiropyrans as Promising Blocks for Polyfunctional Materials

Abstract

ABSTRACT Molecular and crystalline strucutre has been studied for the single crystals of neutral spiropyran (SP) 1,3,3,6′-tetramethylspiro[indoline-2,2′-[2H]pyran[3,2-b] pyridine ( Ia ) and its salts, 1,3,3,5′,6′-pentamethylspiro[indoline-2,2′-[2H]pyran[3,2-b]pyridinium] iodide ( I ) and 5′-hydroxymethyl-1,3,3,7′,8′-pentamethylspiro[indoline-2,2′-[2H]pyran[3,4-b]-pyridinium iodide ( II ). Compounds are monoclinic, i.e., for Ia : a = 11,942(2), b = 11,733(2), c = 11,493(2) A˚, α = 90°. β = 96,96(3)°, γ = 90°, V = 1568,5(5) A˚, ρcalc. = 1.215 g/cm3, Z = 4; I : a = 24.107(5), b = 10.959(2), c = 15.557(2) A˚, α = 90°, β = 108.74°(3), γ = 90°, V = 3892.1(13), A˚3, ρ calc. = 1.482 g/cm3, Z = 8, space group P2(1)/c, while for compound II a = 12.789(3), b = 10.807(2), c = 15.612(3) A˚, α = 90°, β = 108.09°(3), γ = 90°, V = 2050.8(7) A˚3, ρcalc = 1.578 g/cm3, space group P2(1)/n, Z = 4. The crystalline structure of salts I and II differs from that of the neutral SP being formed by the cationic layers separated by I− ions, thus providing a sufficient volume for spiropyran phototransformations. Photochromism of I and II single crystals has been first studied. The quantum yield of the open form formation is about 0.1, and of bleaching 0.04. Tenfold reversible photocycling reduces absorption of the colored form by 10% Photochromic properties have been correlated with the single crystals structure.