Synthesis of New Chlorin e6 Trimethyl and Protoporphyrin IX Dimethyl Ester Derivatives and Their Photophysical and Electrochemical Characterizations

• Published in: Chemistry : a European journal Vol. 20; no. 42; pp. 13644 - 13655
• Main Authors: Menezes, José C. J. M. D. S., Faustino, M. Amparo F., de Oliveira, Kleber T., Uliana, Marciana P., Ferreira, Vitor F., Hackbarth, Steffen, Röder, Beate, Teixeira Tasso, Thiago, Furuyama, Taniyuki, Kobayashi, Nagao, Silva, Artur M. S., Neves, M. Graça P. M. S., Cavaleiro, José A. S.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 13.10.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Anisotropy; Chemical synthesis; Chemistry; Chemistry, Multidisciplinary; Chlorin e6; Circular dichroism; Coordination Complexes - chemical synthesis; Coordination Complexes - chemistry; Correlation analysis; Coumarin; Cycloaddition Reaction; Dichroism; Electrochemical Techniques; Electrochemistry; Flash photolysis; Fluorescence; hetero Diels-Alder; Knoevenagel; Methylation; Molecular orbitals; NMR; Nuclear magnetic resonance; Photodynamic therapy; Photolysis; photophysics; Photosensitizing Agents - chemical synthesis; Photosensitizing Agents - chemistry; Physical Sciences; porphyrinoids; Porphyrins - chemical synthesis; Porphyrins - chemistry; Protoporphyrin; Protoporphyrin IX; Protoporphyrins - chemical synthesis; Protoporphyrins - chemistry; Quinones; Science & Technology; Singlet oxygen; Spectra; Spectroscopy; Spectrum Analysis; Zinc - chemistry; porphyrinoids; Chlorine; Knoevenagel; PORPHYRINS; photophysics; MAGNETIC CIRCULAR-DICHROISM; hetero Diels-Alder; METALLOPORPHYRINS; Chlorin e6
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201403214

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 ZnII 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 ZnII 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 ZnII 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 ZnII complexes were also carried out to gain insights into their behavior for such applications. Natural hybrid photosensitizers: The synthesis of new chlorin e6 trimethyl ester and protoporphyrin IX dimethyl ester dyads as free bases and ZnII complexes in high yields is reported. All compounds were fully characterized by 1D and 2D NMR techniques, UV/Vis spectroscopy, and HRMS. Their photophysical and electrochemical properties were evaluated. Magnetic circular dichroism and circular dichroism spectra were also recorded.