The substitution of Mg2+ with Mn2+/4+ metal ions in chlorophyll structure isolated from Gliricidia sepium leaves

Abstract

One of the critical issues of using chlorophyll (Mg-Chl) as a dye photosensitizer in DSSC is related to a rapid decay of this material. Changing the alkali metal using transition metal ions could theoretically increase the stability of chlorophyll. In this research, the substitution of Mg2+ with Mnn+ ions (n = 2 and 4) in chlorophyll structure isolated from Gliricidia sepium leaves had been carried out. The column chromatography technique was chosen to separate the chlorophyll followed by modifying the metal centre using two different compounds containing manganese, namely MnCl2 and MnO2. The results show that there are differences in Rf values after substitutions, [0.90 (Mg-Chl), 0.81 (Mn2+-Chl), and 0.96 (Mn4+-Chl)]. The Soret bands experience a redshift from 330 to 338 nm for Mn2+-Chl and a blue shift from 411 to 401 nm for Mn4+-Chl while the Q band has a redshift from 665 to 668 nm for Mn2+-Chl but a blue shift from 665 to 526 nm for Mn4+-Chl. The obtained products have similar IR absorption patterns to Mg-Chl but differ only in its transmittance with slightly higher wavenumbers shifts. Shifting of UV-Visible and Infra-red characteristics indicate different molecular electronic nature of the obtained compounds. This implies successful substitution for the metal centre without damaging the structure of the chlorophyll.