Abstract:
Potential photosensitizing property of three new natural plant pigment extracts and variation of their UV-vis spectra with pH have been
investigated. The pigment-extracts were obtained from fruits of Basella alba
(spinach), Brassica oleracea (red cabbage) and sawdust of Artocarpus
heterophyllus (Jack tree). The extraction efficiency of the pigments of fruit
of spinach into water, ethanol and methanol was also studied at three
different temperatures. The best extraction efficiency was achieved in water
at low temperature, however, the stability of the spinach pigments in water
was very poor. Therefore, pigment mixture of fruits of spinach extracted into
80% methanol, which was quite stable at room temperature was used for
further studies. The colour of this pigment extracts remained unchanged
under acidic conditions. The variation of λmax of the UV-vis absorption
spectrum of the pigment extract with pH was studied. A hypsochromic shift
of the spectrum was seen, indicating a decrease in conjugation with
increasing pH. Photosensitizing nature of this pigment extract was studied by
preparing a Dye Sensitized Solar Cell (DSSC) and found to be effective in
photosensitization. Pigments of red cabbage were extracted into water and
the variation of λmax of the UV-vis spectrum of this pigment-extract with pH
was also studied. It showed a bathochromic shift of its λmax with increasing
pH. This pigment extract also showed photosensitizing property when used
in DSSC. The pigments of sawdust of Jack tree were extracted into dilute
NaOH and the variation of UV-vis spectra of this pigment extract with pH
was also studied. This pigment extract did not show any photosensitizing
properties when used in DSSC. Pigment extract of this species was found to
be highly fluorescent and could well be the reason for poor sensitizing
property in solar cell.