2.1 Porphyrins are involved in photosynthesis in plants
(excellent light-trapping properties).
Sunlight is the most abundant source of energy on Earth and is the
source of various bioenergy production. Phototrophic organisms are able
to access this light energy and convert it into chemical energy through
the process of phototropic charge separation(Harmatys et al. 2019). In
ecosystems, the chemical energy required for life is obtained mainly
through the conversion of light energy by photosynthesis(Mirkovic et al.
2017), and porphyrins are essential pigments for many biological energy
transfer processes in plants, algae and bacteria(Shen et al. 2015; Xie
et al. 2020; Zhu et al. 2019a). Chlorophyll is a magnesium
(Mg)-tetrapyrrole molecule (Fig. 2) that plays a crucial role in
photosynthesis. The functions of chlorophylls include capturing light
energy, transporting excitation energy down to the reaction center on a
time scale of 10-100 ps, and driving charge separation reactions at the
reaction center(Croce and van Amerongen 2014; Park et al. 2021). These
molecules contain similar five-membered ring structures, but with
different side chains or reduced states(Chen 2014). Variations in the
rings or side chains in different types of chlorophyll result in
different absorption properties, allowing the organism to capture
different wavelengths of sunlight and enhance light energy harvesting
efficiency(Chen and Scheer 2013). The ability of chlorophylls to convert
light energy into chemical energy has made porphyrins popular in light
energy capture research. Chlorophyll is widely found in nature and is a
key substance for plants and some bacteria to capture light energy and
produce organic matter, which is the basis for people’s survival. For
this reason, there is an urgent need to enter a new field in the study
of porphyrins and expect to move to a higher level.
Fig. 2 Chemical structure of chlorophyll (Chls).