Various iridium complexes consisting of phenylpyrazole (ppz) ligands and isoquinolinecarboxylic acids (iq) as ancillary ligands were designed by energy band-gap calculations via ab initio calculations and synthesized to give rise to various emission wavelengths as expected. Fine color tuning was achieved through varying the position of the methyl substituent on the phenylpyrazole moiety with HOMO electron densities. Additional color tuning was made possible by altering the LUMO through the use of different ancillary ligands such as 1-isoquinolinecarboxylic acid (1iq) and 3-isoquinolinecarboxylic acid (3iq).

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A series of efficient light-harvesting systems (FIr3mGx, x = 1−3) based on dendrimer donor (mCP:  N,N‘-dicarbazolyl-3,5-benzene) derivatives coupled with a sky blue phosphorescent acceptor (FIrpic:  iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C 2‘]-3-hydroxypicolinate derivative) were prepared, and their photophysical properties were investigated. The light-harvesting ability of FIr3mGx (x = 1−3) increases with the number of energy donor mCP units. The acceptor PL intensity of the donor−acceptor conjugate dendrimers (FIr3mGx, x = 1−3) increases over 6 times with the number of mCP units via sensitization from the light-harvesting antenna after excitation at the donor absorption (λex = 310 nm), as compared to that of only an acceptor without a donor (FIrpic) upon excitation at the MLCT region (λex = 380 nm) because of efficient intramolecular singlet−singlet and triplet−triplet energy transfer from the donor to the acceptor and less luminance quenching induced by the bulky dendrimer structure. The singlet−singlet intramolecular energy transfer in FIr3mGx from the dendrimer donor to the acceptor exhibits a high efficiency of greater than 90% via the steady-state PL method and 94% via the transient PL method. Additionally, the triplet−triplet energy transfer efficiency via the transient PL method exhibits an efficiency greater than 99%. This indicates that FIr3mGx exhibits good light-harvesting abilities because the mCP unit is an efficient light absorber and because the core FIrpic functions as a spatial energy concentrator that drains energy from the dendrimer donor.