title: Synthesis of new chlorin e6 trimethyl and protoporphyrin IX dimethyl ester derivatives and their photophysical and electrochemical characterizations.
abstract: In view of increasing demands for efficient photosensitizers for photodynamic therapy (PDT), we herein report the synthesis and photophysical characterizations of new chlorin e6 trimethyl ester and protoporphyrin IX dimethyl ester dyads as free bases and Zn(II) complexes. The synthesis of these molecules linked at the β-pyrrolic positions to pyrano[3,2-c]coumarin, pyrano[3,2-c]quinolinone, and pyrano[3,2-c]naphthoquinone moieties was performed by using the domino Knoevenagel hetero Diels-Alder reaction. The α-methylenechromanes, α-methylenequinoline, and ortho-quinone methides were generated in situ from a Knoevenagel reaction of 4-hydroxycoumarin, 4-hydroxy-6-methylcoumarin, 4-hydroxy-N-methylquinolinone, and 2-hydroxy-1,4-naphthoquinone, respectively, with paraformaldehyde in dioxane. All the dyads as free bases and as Zn(II) complexes were obtained in high yields. All new compounds were fully characterized by 1D and 2D NMR techniques, UV/Vis spectroscopy, and HRMS. Their photophysical properties were evaluated by measuring the fluorescence quantum yield, the singlet oxygen quantum yield by luminescence detection, and also the triplet lifetimes were correlated by flash photolysis and intersystem crossing (ISC) rates. The fluorescence lifetimes were measured by a time-correlated single photon count (TCSPC) method, fluorescence decay associated spectra (FDAS), and anisotropy measurements. Magnetic circular dichroism (MCD) and circular dichroism (CD) spectra were recorded for one Zn(II) complex in order to obtain information, respectively, on the electronic and conformational states, and interpretation of these spectra was enhanced by molecular orbital (MO) calculations. Electrochemical studies of the Zn(II) complexes were also carried out to gain insights into their behavior for such applications.
authors.affiliation: Department of Chemistry and QOPNA, University of Aveiro, 3810-193 Aveiro (Portugal), Fax: (+351)234-401-470.
authors.forename: José C J M D S
authors.initials: JC
authors.lastname: Menezes
authors.forename: M Amparo F
authors.initials: MA
authors.lastname: Faustino
authors.forename: Kleber T
authors.initials: KT
authors.lastname: de Oliveira
authors.forename: Marciana P
authors.initials: MP
authors.lastname: Uliana
authors.forename: Vitor F
authors.initials: VF
authors.lastname: Ferreira
authors.forename: Steffen
authors.initials: S
authors.lastname: Hackbarth
authors.forename: Beate
authors.initials: B
authors.lastname: Röder
authors.forename: Thiago
authors.initials: T
authors.lastname: Teixeira Tasso
authors.forename: Taniyuki
authors.initials: T
authors.lastname: Furuyama
authors.forename: Nagao
authors.initials: N
authors.lastname: Kobayashi
authors.forename: Artur M S
authors.initials: AM
authors.lastname: Silva
authors.forename: M Graça P M S
authors.initials: MG
authors.lastname: Neves
authors.forename: José A S
authors.initials: JA
authors.lastname: Cavaleiro
mesh_terms: D002735:Chlorophyllides; D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry; D061565:Cycloaddition Reaction; D055664:Electrochemical Techniques; D008745:Methylation; D017319:Photosensitizing Agents / Q000138:chemical synthesis* / Q000737:chemistry; D011166:Porphyrins / Q000138:chemical synthesis* / Q000737:chemistry; D011524:Protoporphyrins / Q000138:chemical synthesis* / Q000737:chemistry; D013057:Spectrum Analysis; D015032:Zinc / Q000737:chemistry*
chemical_list: D002735:Chlorophyllides; D056831:Coordination Complexes; D017319:Photosensitizing Agents; D011166:Porphyrins; D011524:Protoporphyrins; C062985:phytochlorin; D015032:Zinc; C041104:dimethyl protoporphyrin IX
keywords: Chlorin e6; Knoevenagel; hetero Diels-Alder; photophysics; porphyrinoids