Amphiphilic chlorins and bacteriochlorins in micellar environments. Molecular design, de novo synthesis, and photophysical properties
作者:Kunche Aravindu、Olga Mass、Pothiappan Vairaprakash、Joseph W. Springer、Eunkyung Yang、Dariusz M. Niedzwiedzki、Christine Kirmaier、David F. Bocian、Dewey Holten、Jonathan S. Lindsey
DOI:10.1039/c3sc51335a
日期:——
The incorporation of amphiphilic tetrapyrrole macrocycles in organized media is of great value for a variety of fundamental photochemical studies, yet work to date has chiefly employed porphyrins rather than chlorins or bacteriochlorins. The latter absorb strongly in the red or near-infrared spectral region, respectively. Here, eight amphiphilic macrocycles (six chlorins and two bacteriochlorins) have been designed, synthesized and characterized; the compounds differ in long wavelength absorption (610–745 nm) and peripheral substituents (type of auxochrome, hydrophobic/hydrophilic groups). A methyl pyridinium or benzoic acid substituent at the 15-position provides a polar “tail” whereas a hydrophobic group distal thereto (in the chlorins) provides a lipophilic “head” for the spontaneous incorporation in organized media. The eight (bacterio)chlorins are characterized by static and time-resolved absorption and fluorescence spectroscopy in N,N-dimethylformamide (DMF) and three micellar environments (TX-100, CTAB, and SDS) as well as ultrafast transient absorption studies in DMF. In most cases, a long-lived excited singlet state was observed [free base chlorins (Φf = 0.14–0.20; τS = 7.9–12.1 ns; Φisc = 0.5), zinc chlorins (Φf = 0.08–0.19; τS = 2.0–3.4 ns; Φisc = 0.6–0.8) and free base bacteriochlorins (Φf = 0.06–0.16; τS = 1.8–4.6 ns; Φisc = 0.4)]. In the case of bacteriochlorins, minimal medium dependence was observed whereas changing the hydrophilic group from methyl pyridinium to benzoic acid increases the fluorescence yield and excited-state lifetime by 50%. In the case of chlorins, the zinc chelate with methyl pyridinium substitution exhibits substantial environmental dependence due to interaction of the solvent with the methyl pyridinium group and the central zinc metal. Collectively, the studies provide valuable information for the design of red or near-infrared absorbing chromophores for incorporation into amphiphilic environments such as micelles, membranes, or proteins.
在有组织介质中加入两亲性四吡咯大环对于各种基础光化学研究具有重要价值,但迄今为止的工作主要采用的是卟啉而不是氯素或细菌氯素。后者分别在红光或近红外光谱区吸收强烈。在此,我们设计、合成并鉴定了八种两亲大环(六种氯素和两种细菌氯素);这些化合物在长波长吸收(610-745 纳米)和外围取代基(辅助色素类型、疏水/亲水基团)方面各不相同。位于 15 位的甲基吡啶或苯甲酸取代基提供了极性 "尾部",而位于其远端(在氯素中)的疏水基团则提供了亲脂性 "头部",以便自发地掺入有组织的介质中。通过在 N,N-二甲基甲酰胺(DMF)和三种胶束环境(TX-100、CTAB 和 SDS)中进行静态和时间分辨吸收和荧光光谱分析,以及在 DMF 中进行超快瞬态吸收研究,对这八种(细菌)氯化物进行了表征。在大多数情况下,都观察到了长寿命激发单线态[游离碱基氯素(Φf = 0.14-0.20; τS = 7.9-12.1 ns; Φisc = 0.5)、锌氯素(Φf = 0.08-0.19; τS = 2.0-3.4 ns; Φisc = 0.6-0.8) 和游离碱基细菌氯化物 (Φf = 0.06-0.16; τS = 1.8-4.6 ns; Φisc = 0.4)]。对于细菌氯素,观察到的介质依赖性很小,而将亲水基团从甲基吡啶改为苯甲酸,则会使荧光产率和激发态寿命增加 50%。就氯素而言,甲基吡啶取代的锌螯合物表现出很大的环境依赖性,这是由于溶剂与甲基吡啶基团和中心金属锌相互作用的结果。总之,这些研究为设计红色或近红外吸收发色团提供了宝贵的信息,这些发色团可用于胶束、膜或蛋白质等两亲环境中。