Comparison of oxyferrous PGIS complexes in solution and in sol–gel. (A) Absorption spectra of PGIS (solid line) and its oxyferrous complex formed at 1.5 h (dotted line), 2.5 h (dashed line) and 4 h (dot–dot–dash line) in the sol–gel. (B) Left panel, absorption spectra of 4.6 µm ferric PGIS (solid line) and ferrous PGIS (dotted line) in solution. Right panel, ferric PGIS (thin solid line), ferrous PGIS (dashed line), re-oxidized PGIS (dash-dot-dot line) and oxyferrous PGIS (thick solid line) in sol–gel.