Intermolecular energy transfer involving an iridium complex studied by a combinatorial method.
A recently developed combinatorial method utilizing angular dependence of evaporation rate was used to create compositional spread thin film libraries of Tris(2-pyridin-2-yl-indolizino[3,4,5-ab] isoindole-C(1), N('))iridium(III) [Ir(pin)(3)] and 4,4(')-N,N(')-dicarbazol-biphenyl (CBP) composite, with the molar fraction of Ir(pin)(3) complex varying in the 0.0003<chi(Ir(pin)(3) )<0.96 range. Spatially correlated absorbance and photoluminescence (PL) measurements were used to quantify luminescence quenching of photo-excited CBP molecules by the Ir(pin)(3) complex as a function of the average distance between two molecules. It was found that the CBP-->Ir(pin)(3) energy transfer proceeds by the Forster mechanism with the Forster radius of 30 A. The CBPxIr(pin)(3) composite has the highest photoluminescence quantum efficiency approximately 0.95, for chi(Ir(pin)(3) )=0.03 and is characterized by a structured green emission (lambda(max)=538 nm) originating from the ligand-centered (pi-pi(*))(3) state of the Ir(pin)(3) complex. On the contrary, the PL spectra of Ir(pin)(3) bulk are characterized by a weak red emission (lambda(max)=673 nm) attributed to the lowest metal-to-ligand charge transfer state. A statistical analysis based on a binomial distribution indicates that the emission from the (pi-pi(*))(3) state is quenched in Ir(pin)(3) molecules that are in a direct contact with each other.
Suljovrujic
E
E
Institute for Quantum Engineering, Science and Technology, University of California, Santa Barbara, California 93106, USA.
Ignjatovic
A
A
Srdanov
V I
VI
Mitsumori
T
T
Wudl
F
F