462
K. Imato and Y. Ooyama
Fig. 13.9 Photosensitizing dyes based on transition metal complexes: a Ru, b Ir, and c Pt metal
complexes
long-lived τ T and high Φ values (Fig. 13.9b, [Ir(ppy) 2 (acac)], [Ir(bt) 2 (acac)],
[Ir(btp) 2 (acac)]) (Stacey and Pope 2013; Djurovich et al. 2007). For example,
the Φ value of a cyclometalated Ir(III) complex with 2-phenylpyridine (ppy) and
acetylacetone (acac) ([Ir(ppy) 2 (acac)]) is 0.9.
Pt(II) complexes show excellent
1 O 2 generation characteristics, although some
of them are photochemically unstable (Fig. 13.9c). Cyclometal-diketonated Pt(II)
complexes with monoanionic ligands (CˆN) ([Pt(CˆN)(OˆO)]) have broad absorption bands derived from MLCT around 350–450 nm (ε = 2000–6000 M
–1 cm
–1 ).
For example, [Pt(ppy)(acac)] and [Pt(btp)(acac)] (acac: acetylacetone) with 2phenylpyridine (ppy) and 2,2
-benzothienopyridine (btp) as cyclometalated ligands,
respectively, have photoabsorption bands in short-wavelength regions but show
Φ values close to 1 in deuterated methanol (Djurovich et al. 2007). The relatively strong MLCT photoabsorption bands of diimine-aryldithiolate platinum(II)
complexes ([Pt(SˆS)(mesBIAN)]) (mesBIAN: bismesitylbiazanaphthenequinone)