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      Retaining individualities: the photodynamics of self-ordering porphyrin assemblies†

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          Abstract

          Retained photochemical properties – a simple porphyrin–polyDMA conjugate with the ability to self assemble into large (∼1 μm) vesicles in water. The photodynamics are remarkably preserved despite the extensive aggregation.

          Abstract

          The retention of photochemical properties of individual chromophores is a key feature of biological light harvesting complexes. This is achieved despite extensive aggregation of the chromophores, which in synthetic chromophore assemblies often yields a change in spectral characteristics. As an alternative approach towards mimicking biological light harvesting complexes, we report the synthesis of porphyrin assemblies which retained the photochemical properties of the individual chromophore units despite their substantial aggregation. These new materials highlight a new bottom-up approach towards the design and understanding of more complex biomimetic and naturally occurring biological systems.

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          Most cited references57

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          Cross-linked block copolymer micelles: functional nanostructures of great potential and versatility.

          Rachel O’Reilly, Craig Hawker, Karen L. Wooley (2006)
          Supramolecular self assembly techniques have provided a versatile means by which to selectively assemble polymer molecules into well-defined three dimensional core-shell nanostructures. The covalent stabilisation and tailoring of these dynamic nanostructures can be achieved using a range of chemistries within the assembly to afford robust functional nanoparticles. Many examples of the stabilisation, functionalisation and decoration of these nanoparticles have been reported in the literature and this tutorial review will focus on these recent developments and highlight their potential applications.
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            Discrete cyclic porphyrin arrays as artificial light-harvesting antenna.

            Naoki Aratani, Dongho Kim, Atsuhiro Osuka (2009)
            The importance of photosynthesis has driven researchers to seek ways to mimic its fundamental features in simplified systems. The absorption of a photon by light-harvesting (antenna) complexes made up of a large number of protein-embedded pigments initiates photosynthesis. Subsequently the many pigments within the antenna system shuttle that photon via an efficient excitation energy transfer (EET) until it encounters a reaction center. Since the 1995 discovery of the circularly arranged chromophoric assemblies in the crystal structure of light-harvesting antenna complex LH2 of purple bacteria Rps. Acidophila, many designs of light-harvesting antenna systems have focused on cyclic porphyrin wheels that allow for efficient EET. In this Account, we review recent research in our laboratories in the synthesis of covalently and noncovalently linked discrete cyclic porphyrin arrays as models of the photosynthetic light-harvesting antenna complexes. On the basis of the silver(I)-promoted oxidative coupling strategy, we have prepared a series of extremely long yet discrete meso-meso-linked porphyrin arrays and covalently linked large porphyrin rings. We examined the photophysical properties of these molecules using steady-state absorption, fluorescence, fluorescence lifetime, fluorescence anisotropy decay, and transient absorption measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly related to the EET processes within the porphyrin rings. Within these structures, the exciton-exciton annihilation time and the polarization anisotropy rise time are well-described in terms of the Forster-type incoherent energy hopping model. In noncoordinating solvents such as CHCl(3), meso-pyridine-appended zinc(II) porphyrins and their meso-meso-linked dimers spontaneously assemble to form tetrameric porphyrin squares and porphyrin boxes, respectively. In the latter case, we have demonstrated the rigorous homochiral self-sorting process and efficient EET along these cyclic porphyrin arrays. The meso-cinchomeronimide appended zinc(II) porphyrin forms a cyclic trimer. We have also shown that the corresponding meso-meso-linked diporphyrins undergo high-fidelity self-sorting assembling to form discrete cyclic trimer, tetramer, and pentamer with large association constants through perfect discrimination of enantiomeric and conformational differences of the meso-cinchomeronimide substituents. Collectively, these studies of covalently and noncovalently linked discrete cyclic porphyrin arrays aid in the understanding of the structural requirements for such very fast EET in natural light-harvesting complexes.
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              Photodynamic therapy in oncology: mechanisms and clinical use.

              Robert H Pass (1993)
              In photodynamic therapy (PDT), a sensitizer, light, and oxygen are used to cause photochemically induced cell death. The mechanism of cytotoxicity involves generation of singlet oxygen and other free radicals when the light-excited sensitizer loses or accepts an electron. Although selective retention of sensitizer by malignant tissue is seen in vivo, the mechanisms for this sensitizer targeting remain unclear. The first-generation sensitizers are porphyrin based and vary in lipophilicity and hydrophilicity. Targeting of the vasculature seems to be a prominent feature of the cytotoxic effect of these sensitizers in vivo, with resulting necrosis. Treatment depth varies with the wavelength of light that activates the sensitizer used, and the second-generation sensitizers are activated at longer wavelengths, allowing for a 30% increase in treatment depths. The selectivity of targeting can be increased when the sensitizer is delivered with the use of liposomes or monoclonal antibodies specific for tumor antigens. Studies have demonstrated direct effects of PDT on immune effector cells, specifically those with lineage from macrophages or other monocytes. Clinically, this therapy has been chiefly used for palliation of endobronchial and esophageal obstruction, as well as for treatment of bladder carcinomas, skin malignancies, and brain tumors. The future of PDT rests in defining its use either as an intraoperative adjuvant to marginal surgical procedures or as a primary treatment for superficial malignancies. Phase III trials in esophageal cancer and lung cancer are in progress and will help in evaluation of whether Photofrin II, the most widely used sensitizer, can be added to the oncologic armamentarium, pending approval from the U.S. Food and Drug Administration.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Chem Commun (Camb)
                Journal ID (iso-abbrev): Chem. Commun. (Camb.)
                Title: Chemical Communications (Cambridge, England)
                Publisher: Royal Society of Chemistry
                ISSN (Print): 1359-7345
                ISSN (Electronic): 1364-548X
                Publication date (Print): 31 January 2016
                Publication date (Electronic): 18 December 2015
                Volume: 52
                Issue: 9
                Pages: 1938-1941
                Affiliations
                [a ] Department of Chemistry , University of Warwick , Gibbet Hill Road , Coventry , UK . Email: v.stavros@ 123456warwick.ac.uk ; Email: rachel.oreilly@ 123456warwick.ac.uk
                [b ] Molecular Organisation and Assembly of Cells Doctoral Training Center (MOAC DTC) , University of Warwick , Gibbet Hill Road , Coventry , UK
                [c ] School of Chemistry & Institute for Life Sciences , University of Southampton , Highfield , Southampton , UK
                [d ] School of Life Science , University of Warwick , Gibbet Hill Road , Coventry , UK
                Article
                Publisher ID: c5cc09095d
                DOI: 10.1039/c5cc09095d
                PMC ID: 4720934
                PubMed ID: 26680651
                SO-VID: c4767f8c-eaca-47f6-b1f8-5982da5d041a
                Copyright © This journal is © The Royal Society of Chemistry 2015
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 2 November 2015
                Date accepted : 1 December 2015
                Categories
                Subject: Chemistry

                Notes

                †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5cc09095d


                ScienceOpen disciplines: General chemistry
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                ScienceOpen disciplines: General chemistry

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