The electron transfer rate of large TPA based compounds: a joint theoretical and electrochemical approach

A series of triphenylamine (TPA) based compounds is investigated by means of density functional theory and cyclic voltammetry. Using the Nicholson\u27s formalism, the measured D E_p are correlated with B3LYP/6-31G* calculated reorganization energies (lambda), elucidating the trend followed by the self electron transfer rate (k_{ET}) of these compounds. Besides the direct dependency upon the dimension of the cationic fragment contributing to the hole stabilization, the lambdas are tuned by the symmetry local to the TPA units, as evidenced by the structural relaxation of the cations. TAPC turns out to be the most effective compound with respect to the self electron transfer process, while N,N\u27-diphenyl-N,N\u27-bis[N-phenyl-N-3-tolyl(4-aminophenyl)]benzidine (MDTAB) shows the interesting combination of low ionization potential (IP) and high k_{ET}. This can make these compounds interesting for practical applications in organic light emitting diodes (OLEDs) devices, due to the direct correlation of the IP and k_{ET} with the hole transfer efficiency to the anode, along with the hole mobility

A correlation between electrochemical properties and geometrical structure of some triarylamines used as hole transporting materials in organic electroluminescent devices

Two new compounds with four tertiary arylamine moieties connected in a fully para-conjugated system have been synthesised in order to obtain new molecules having low ionisation potentials, as required for hole transporting materials in Organic Light Emitting Diodes (OLEDs). Their electrochemical properties have been measured and compared to seven di erent commercial triarylamines tested in the same experimental conditions. Using the AM1 geometries and the statistical average of orbital potential method (SAOP), the redox potentials of the molecules have been estimated and found to be in good agreement with the experimental data. An evident correlation between the molecular geometry and the electrochemical potential of the rst oxidation exists and shows that, for equal number of para-conjugated triarylamine moieties, the starburst con guration is more e cient than the linear one in lowering the oxidation potential and that the amine moieties of the inner sphere play a more important role than those of the outer sphere. Besides, amine moieties connected by a biphenyl bridge show generally higher ionisation potentials than those connected via one phenylene

N∧C∧N-coordinated platinum(II) complexes as phosphorescent emitters in high-performance organic light-emitting devices

A series of terdentate cyclometallated PtII complexes with remarkable luminescence properties are used as new phosphorescence-emitting dopants in a blended host matrix as the emitting layer, resulting in very high electroluminescence efficiencies. Because of the high phosphorescence quantum yields of these Pt complexes and the efficient energy transfer from both singlet and triplet excited states of the host to the emitting guest, external electroluminescence quantum efficiencies as high as 4-16 % photons per carrier and luminous efficiencies of 15-40 cd A-1 are achieved. Moreover, these high efficiency values were maintained over a four-decade current intensity span with no significant roll-off. Tuning of the electroluminescence spectra from the yellow to the green-bluish region of the chromaticity diagram is obtained simply by changing the substituents at the central 5-position of the cyclometallating ligand

Platinum and palladium complexes of fluorenyl porphyrins as red phosphors for light-emitting devices

International audiencePlatinum(II) and palladium(II) complexes of a porphyrin with fluorenyl groups linked directly at the meso-positions (TFP) have been synthesized and characterized. Their luminescence properties in solution have been studied under ambient conditions and at 77 K. Compared to the corresponding complexes of tetraphenylporphyrin TPP, the emission is red-shifted in both cases. Radiative rate constants are found to be enhanced by the fluorenyl substituents, although non-radiative decay rates are also increased in solution. Short-wavelength UV excitation leads to no detectable fluorenyl-based fluorescence, indicating that very efficient transfer of energy to the porphyrin occurs. An OLED in which PtTFP is used as a red phosphor has been prepared and its electroluminescence performance assessed. High current "roll-off" is significantly delayed to higher currents compared to previously described OLEDs that make use of standard platinum porphyrins as emitters, an effect which can be attributed to the shorter radiative lifetime of PtTFP

Phosphorescence quantum yield enhanced by intermolecular hydrogen bonds in Cu4I4 clusters in the solid state

Organo-copper(I) halide complexes with a Cu4I4 cubane core and cyclic amines as ligands have been synthesized and their crystal structures have been defined. Their solid state photophysical properties have been measured and correlated with the crystal structure and packing. A unique and remarkably high luminescence quantum yield (76%) has been measured for one of the complexes having the cubane clusters arranged in a columnar structure and held together by N–HI hydrogen bonds. This high luminescence quantum yield is correlated with a slow radiationless deactivation rate of the excited state and suggests a rather strong enhancement of the cubane core rigidity bestowed by the hydrogen bond pattern. Some preliminary thin film deposition experiments show that these compounds could be considered to be good candidates for applications in electroluminescent devices because of their bright luminescence, low cost and relatively easy synthesis processe

Exciton coupling in molecular salts of 2-(1,8-naphthalimido)ethanoic acid and cyclic amines: modulation of the solid-state luminescence

In this study we have purposely altered the solid state luminescence properties of 2-(1,8-naphthalimido)ethanoic acid (NEaH) (0) via molecular salts formation with cyclic amines such as 1,4-diazabicyclo[2.2.2]octane (DABCO), quinuclidine (ABCO), 3-quinuclidinol (OH-ABCO), and piperazine (PIP). All crystalline materials have been characterized in the solid state via single-crystal and variable temperature powder X-ray diffraction and thermal methods; luminescence spectra in the solid state have been recorded. Exciton interactions have been determined with quantum-chemical calculations for all molecular organic salts, and tuning of their magnitude in response to changes in the crystal packing has been demonstrated. It is suggested that the variations in photoluminescence can be interpreted on the basis of the different excitonic interactions amongst the naphthalimide moieties