Theoretical studies on electronic and electron blocking properties of iridium complexes with phenylpyrazolato ligands

The tris(1-phenylpyrazolato,N,C2′)iridium(III) Ir(ppz)3, (fac-Ir(ppz)3, 1; mer-Ir(ppz)3, 2) and iridium(III)bis(1-phenylpyrazolato,N,C2′) (2,2,6,6-tetramethyl-3,5-heptane-dionato-O,O) ppz2Ir(dpm) (C-cis,N-trans-ppz2Ir(dpm), 3; C-cis,N-cis-ppz2Ir(dpm), 4) have been investigated theoretically to explore their electronic structures, spectroscopic and electron blocking properties. A detailed comparison of the electronic structure characteristics of the two isomers has been addressed for pointing out differences in absorption and emission properties. The geometries and electronic structures are investigated at B3LYP and CIS levels for ground and excited states, respectively. At the TD-DFT and PCM levels, 1–4 give rise to absorptions at 329, 346, 355 and 347 nm, respectively, and phosphorescent emissions at 377, 461 and 405 nm for 1–3, respectively. The transitions of 1–2 are attributed to [d(Ir) + π(phenyl)] → [π*(pyrazolyl)] charge transition, whereas 3–4 are related to [d(Ir) + π(phenyl)] → [π*(pyrazolyl) + π*(dpm)]. The reorganization energies computed for hole (λhole) except 2 are smaller than that of N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine which is a typical hole transport material. Fac-Ir(ppz)3 is the most efficient electron blocking material among the four complexes.