Synthesis and Property of Dichroic Photochromism of Bipyridinium Bis(phosphonate)s

4,4′-联吡啶的双季盐通过单电子光化学反应转化为强蓝色自由基阳离子。为了评价可逆光还原性（光致变色），研究了具有较好亲核性和各向异性的烷烃膦酸盐阴离子的合成及其二色性。采用两步Menshutkin反应制备了N，N'-二烷基-4,4'-联吡啶二卤化物，并用阴离子交换树脂将其与烷基膦酸盐交换。^ h - nmr和元素分析表明，viologens由两个膦酸盐阴离子组成，并且吡啶环上的质子被转移到更高的场，可能是由于与大体积的二价膦酸盐阴离子的低静电相互作用。这导致膦酸盐热不稳定，在相对较低的温度下分解而不熔化。在具有高电离势的有机溶剂中，近紫外辐射形成的自由基很少。在具有给电子性质（低IP）的高稀释溶剂中，光还原主要通过与周围溶剂分子的et反应进行。用稳态紫外线照射观察了玻璃夹层pvc膜中的自由基阳离子，自由基阳离子的颜色持续了数天。红外光谱表明，固体膦酸盐的光诱导还原是由紫外光分子内的反阴离子引起的。用烷膦酸逐渐冷却熔融的双膦酸紫罗兰根制备薄膜时，与快速冷却膜相比，二聚体自由基阳离子在530 nm处的吸收增加。虽然吸收差异很小，但在各向异性组织的烷膦酸中，紫素分子的取向使紫素-二膦酸盐的膜呈现二色性。

The viologens, bis-quaternary salts of 4,4'-bipyridine turn to intensive blue radical cations by one-electron by photochemical reaction. With the intention to evaluate the reversible photo-reduction(photochromism), the synthesis and dichroism of viologens with alkanephophonate anions which possess relatively good nucleophilicity and anisotrophic character was investigated. N,N'-dialkyl-4,4'-bipyridinium dihalides were prepared by two steps of Menshutkin reactions with different alkyl halides and their counter ions were exchanged with alkanephosphonates using an anion-exchange resin. ^1H-NMR and elemental analyses indicated that the viologens consist of two phosphonate anions, and protons at pyridinium rings are shifted to higher field, presumably due to low electrostatic interaction with bulky bivalent phophonate anions. This causes that the phosphonate salts are thermally unstable and decompose at relative low temperature without melting.The radical formation by near-UV irradiation is small in organic solvents possessing high ionization potential. The photo-reduction in high-diluted solvents possessing electron-donating property (low IP) mainly proceeds by the ET-reaction from surrounding solvent molecules. The radical cations in glass sandwiched PVC-films were observed by steady state UV-irradiation, and the color of the radical cations persisted for several days. IR-spectra indicate that the photo-induced reduction of solid phosphonate salts proceeds from counter anion within a viologen molecule. When films were prepared by gradually cooling the melted viologen-bisphosphonate with alkanephosphonic acids, the absorption at 530 nm corresponds to the dimeric radical cation increased compared with rapidly cooling ones. While the absorption difference was small, the films of viologen-bisphosphonate salt showed dichroism by the orientation of viologen molecules in anisotropically organized alkanephosphonic acids.