Synthesis of New Chlorin  e 6 Trimethyl and Protoporphyrin IX Dimethyl Ester Derivatives and Their Photophysical and Electrochemical Characterizations

• Published in: Chemistry : a European journal 2014-10, Vol.20 (42), p.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: Article
• Language: English
• 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  e 6 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.