The synthesis, characterization and spectral properties of six new meso-aryl core modified sapphyrins are described. An efficient approach involving an acid catalyzed condensation of bithiophene diol 1 and modified tripyrranes 2a–2e allows preparation of the desired meso-aryl sapphyrins in 16–36% yield. The product distribution and the isolated yield were found to be dependent on the nature of the acid catalyst (Lewis acid or protic acid) and its concentration. Protic acid catalyst exclusively gave the expected sapphyrins while two additional products, an 18π tetraphenylporphyrin and a 26π modified rubyrin, were isolated under Lewis acid catalysis. An analysis of proton NMR and absorption spectral data suggests that in free base sapphyrins, the heterocyclic ring opposite to the bithiophene unit is inverted as in N-5 meso-aryl sapphyrin and the degree of inversion is dependent on the nature of the heterocyclic ring. The energy optimized structure calculated from the semi-empirical method substantiates such a conclusion. Protonation of sapphyrins generates respective mono- and dications and the heterocyclic ring retains an inverted structure in contrast to normal N-5 sapphyrins. The triplet excited lifetimes for free base and protonated derivatives are similar both under argon saturated and air equilibrated conditions, indicating that the triplet state quenching by oxygen is minimal. Cyclic voltammetric studies reveal easier reductions and harder oxidations relative to meso-aryl porphyrins and the Δredox observed for 3d suggests significant reduction of the HOMO–LUMO energy gap consistent with the large red shift observed for the Soret band.
描述了六种新的meso-芳基核心改性萨非林的合成、表征和光谱特性。采用一种高效的方法,通过酸催化的双噻烯二醇1和改性三
吡咯烷2a-2e的凝缩反应,可以在16-36%的产率下制备所需的meso-芳基萨非林。产物分布和分离产率依赖于酸催化剂的性质(
路易斯酸或质子酸)及其浓度。质子酸催化剂仅产生预期的萨非林,而在
路易斯酸催化下则分离出两种额外产物,分别为18π
四苯基卟啉和26π改性红色素。对质子NMR和吸收光谱数据的分析表明,在自由碱萨非林中,与双噻烯单元相对的杂环环结构颠倒,类似于N-5 meso-芳基萨非林,而颠倒的程度依赖于杂环的性质。从半经验方法计算得到的能量优化结构证实了这一结论。萨非林的质子化生成相应的单阳离子和双阳离子,而杂环结构保持颠倒,与正常的N-5萨非林形成对比。在
氩气饱和和空气平衡条件下,自由碱和质子化衍
生物的三重激发寿命相似,表明氧对三重态的淬灭作用很小。循环伏安研究显示,相对于meso-芳基
卟啉,萨非林易于还原而难以氧化,3d中观察到的Δ红ox表明HOMO-LUMO能隙显著减少,与Soret带观察到的红移相一致。