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Issue 9, 2013
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Amphiphilic chlorins and bacteriochlorins in micellar environments. Molecular design, de novo synthesis, and photophysical properties

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Abstract

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.

Graphical abstract: Amphiphilic chlorins and bacteriochlorins in micellar environments. Molecular design, de novo synthesis, and photophysical properties

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Publication details

The article was received on 13 May 2013, accepted on 12 Jun 2013 and first published on 24 Jun 2013


Article type: Edge Article
DOI: 10.1039/C3SC51335A
Citation: Chem. Sci., 2013,4, 3459-3477
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    Amphiphilic chlorins and bacteriochlorins in micellar environments. Molecular design, de novo synthesis, and photophysical properties

    K. Aravindu, O. Mass, P. Vairaprakash, J. W. Springer, E. Yang, D. M. Niedzwiedzki, C. Kirmaier, D. F. Bocian, D. Holten and J. S. Lindsey, Chem. Sci., 2013, 4, 3459
    DOI: 10.1039/C3SC51335A

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