A series of donor−spacer−acceptor triads has been synthesized and fully characterized. Both donor and acceptor units are built from boron dipyrromethene (BODIPY) dyes but they differ in their respective conjugation lengths, and thereby offer quite disparate optical properties. The spacer units comprise an oligomer of 1,4-phenylene-diethynylene repeat units and allow the boron−boron separation distance to be varied progressively from 18 to 38 A. A notable feature of this series is that each subunit can be selectively excited with monochromatic light. Highly efficacious electronic energy transfer (EET) occurs from the first-excited singlet state localized on the conventional BODIPY dye to its counterpart resident on the expanded BODIPY-based nucleus, but the rate constant follows a nonlinear evolution with separation distance. Overall, the rate of EET falls by only a factor of 4-fold on moving from the shortest to the longest spacer. This shallow length dependence is a consequence of the energy gap between ...

Length Dependence for Intramolecular Energy Transfer in Three- and Four-Color Donor-Spacer-Acceptor Arrays

A series of homologous bis-cyclometalated iridium(III) complexes Ir(2,4-di-X-phenyl-pyridine)2(picolinate) (X = H, F, Cl, Br) HIrPic, FIrPic, ClIrPic, and BrIrPic has been synthesized and characterized by NMR, X-ray crystallography, UV–vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the σp and σm Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with FIrPic and ClIrPic, the impact of the large bromine atom remarkably decreases the photolumine...

Influence of halogen atoms on a homologous series of bis-cyclometalated iridium(III) complexes

A series of carbazole derivatives was synthesized and their electrical and photophysical properties were investigated. It is shown that the triplet energy levels of these hosts are higher than that of the most popular blue phosphorescent material iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C-2'] picolinate (FIrpic) and the most extensively used phosphorescent host material 4,4'-N,N'-dicarbazole-biphenyl (CBP). These new host materials also showed good thermal stability and high glass transition temperatures (T-g) ranging from 78 to 115 degrees C as the linkage group between the carbazoles was altered. Photophysical measurements indicate that the energy transfer between these new hosts and FIrpic is more efficient than that between CBP and FIrpic. Devices incorporating these novel carbazole derivatives as the host material doped with FIrpic were fabricated with the configurations of ITO/NPB (40 nm)/host:FIrpic (30 nm)/BCP (15 nm)/AlQ (30 nm)/LiF (1 nm)/Al (150 nm). High efficiencies (up to 13.4 cd/A) have been obtained when 1,4-bis (4-(9H-carbazol-9-yl)phenyl)cyclohexane (CBPCH) and bis(4-(9H-carbazol-9-yl)phenyl) ether (CBPE) were used as the host, respectively.

Nonconjugated Carbazoles: A Series of Novel Host Materials for Highly Efficient Blue Electrophosphorescent OLEDs

The energy transfer cassettes composed of coumarin and Bodipy as well as NIR distyryl Bodipys were designed to capture photonic energy and convert it to longer wavelength fluorescence emission; large pseudo-Stokes' shifts (up to 410 nm) and efficient energy transfer efficiencies (up to 98.6%) as well as a marked antenna effect were demonstrated.

Through-bond energy transfer cassettes based on coumarin–Bodipy/distyryl Bodipy dyads with efficient energy efficiences and large pseudo-Stokes' shifts

Heteroleptic cyclometalated iridium(III) complexes (C^N)2Ir(Bpic) (4–6) (C^N = dfppy (4), ppy (5), btp (6)) supported by triarylborylpicolinate (Bpic) ancillary ligand were synthesized and characterized. X-ray diffraction study of 5 confirmed N^O chelation of the Bpic ligand to the iridium center forming an (C^N)2Ir–borane conjugate. While the UV/vis absorption bands of 4–6 remained almost unchanged in the low-energy region upon fluoride addition, a ratiometric turn-on phosphorescence response was observed for 4 and 5. In contrast, the phosphorescence of 6 was little affected by fluoride binding. Experimental and theoretical studies suggest that the LUMO in neutral 4 and 5 is dominated by the Bpic ligand, which makes the weakly emissive 3ML′CT/3LL′CT (L = C^N; L′ = Bpic) states as the lowest-energy triplet excited state, while the fluoride binding to 4 and 5 induces the highly emissive 3MLCT/3ππ* states centered on the (C^N)2Ir moiety. Thermally induced conversion from the 3MLCT/3ππ* to the 3ML′CT/3LL′CT ...

Heteroleptic cyclometalated iridium(III) complexes supported by triarylborylpicolinate ligand: ratiometric turn-on phosphorescence response upon fluoride binding.

Energy transfer and morphology study of a new iridium based cyclometalated phosphorescent complex

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Energy transfer and morphology study of a new iridium based cyclometalated phosphorescent complex