Photophysical properties of water-soluble porphyrin were studied in aqueous solutions with/without DNA and in DNA solid films. Ultrathin films were prepared from aqueous DNA solutions by a spin-coating method on glass or on gold nanoparticles (AuNPs). Remarkable enhancement of phosphorescence was observed for porphyrin immobilized in DNA films spin-coated on AuNPs, which was attributed to the electric field enhancement and the increased radiative rate by localized surface plasmon resonance of AuNPs.

We investigated luminescent properties in combination of red emissive europium complex of tris(dibenzoylmethane)-mono(4,7-dimethylphenanthroline)europium(III) [Eu(dbm)3phen] and blue phosphorescent molecule of bis[(4,6-difluorophenyl)-pyridinato-N,C2'] (picolinate) iridium (III) (FIrpic) doped in poly(N-vinyl-carbazole) (PVK). A sharp red emission from Eu(dbm)3phen was observed in photoluminescence (PL) measurement, whereas, in the case of electroluminescence (EL), emission from FIrpic and Eu compound were observed. The difference of the PL and EL spectra indicates that different energy transfer processes between Eu(dbm)3phen and FIrpic are suggested.

Newly designed cyclometalated iridium phosphors bearing 2,3-diphenylquinoxalines were characterized to provide highly efficient and vivid-red emitting materials for electrophosphorescent organic light-emitting devices. Excellent quantum efficiencies for photoluminescence (PL) within a range 50-79% were observed in dichloromethane solutions at room temperature. A greatly improved PL decay lifetime of 1.1 µsec was also observed in CBP coevaporated film. Luminescence peak wavelengths of the phosphors lay within a preferable range 653-675 nm in evaporated films. The most vivid-red electroluminescence with 1931 CIE chromaticity coordinates of (x=0.70, y=0.28) was successfully attained.

Theoretical calculation has been done on the decay time of photoluminescence of Ir(ppy)3 dissolved in tetrahydrofuran and its temperature dependence at 1.2-300 K. Taking into account that the emitting triplet state consists of three zero-field splitting substates and taking into account one-phonon non-radiative transitions among these substates, the rate equations for the populations of these substates have been obtained. Three decay components are derived by solving not only the secular equation but also the rate equations, where the slow decay time shows decrease from 145 to 2 µs with increasing temperature from 1.2 to 300 K. A good agreement has been obtained for the temperature dependence between the calculated slow decay time and the observed one.

Charge carrier generation, transport, and exciton diffusion in f ac tris(2-phenylpyridine)iridium(III) Ir(ppy)3 doped in 4,4'-N,N'-dicarbazole-biphenel (CBP) thin films, an emissive layer of green electrophosphorescent devices, have been studied in terms of time-of-flight (TOF) transient photocurrent, steady-state photocurrent and time-resolved photoluminescence (PL) spectroscopies. It is found that the excitation energy rapidly transfer from CBP to Ir(ppy)3, and that the charge carriers are generated on Ir(ppy)3 sites. With increasing Ir(ppy)3 concentration, the electron drift mobility is slightly decreased, while the hole transit signals become unobservable. The electron and hole transport properties of Ir(ppy)3 doped CBP thin films result from the energy levels of the lowest unoccupied molecular orbital and the highest occupied molecular orbital of Ir(ppy)3 with respect to those of CBP. From steady-state photocurrent measurement, the diffusion lengths of 3.5% and 7.0% Ir(ppy)3 doped CBP thin films are determined to be 21 nm and 50 nm, respectively.