The sterically congested tetraarylpyrenes 1-3, which can be readily accessed by Suzuki coupling, exhibit no-aggregation (pi-stacking) behavior in both solution and solid states. The indisposed tendency of 1-3 toward crystallization and their moderate molecular dimensions permit exploitation as blue light emitting materials in OLEDs with respectable device performances.

In this paper we present the synthesis, spectroscopic characterization and theoretical modelling of two pairs of correlated dipolar and octupolar donor-acceptor conjugated chromophores, based on the triphenylamine branching centre. The two pairs of chromophores differ for the electron withdrawing end-groups. Linear absorption, fluorescence and two-photon absorption of all the compounds in different solvents can be well described by the use of charge-resonance theoretical models based on essential-state descriptions of the electronic structure, and taking into account the coupling to effective molecular vibrations and to polar solvation degrees of freedom. On the contrary, the alternative Frenkel exciton model does not provide a good description of the observed behavior. The robustness of the proposed theoretical models is demonstrated for the first time by the fact that the modulation of a single molecular parameter (the one linked to the electron-withdrawing ability of the end groups) is enough to describe the evolution of the spectroscopic properties along the whole series of chromophores, both "intra-pair" and "inter-pair". The effectiveness of the approach suggests that this kind of theoretical modelling can be very useful to predict different properties of the compounds at hand or of correlated structures of increasing complexity, such as dendrons and dendrimers, giving a guide to the synthesis of (macro)molecules for applications in light-emitting and nonlinear optical devices, artificial light-harvesting systems or optical imaging of living tissues.

The unique structural attributes inherent to D(2d)-symmetric rigid tetraarylbimesityls render their close packing in the solid state difficult. We have exploited the indisposed tendency of such modules based on the bimesityl scaffold toward crystallization to design a novel class of amorphous functional materials with high glass transition temperatures and thermal stability (T(d) > 400 degrees C). It is shown that a variety of 2- and 4-fold anthracene-functionalized bimesityls, 1-7, that exhibit excellent amorphous properties (T(g) = ca. 190-330 degrees C) can be readily prepared via facile Pd(0)-mediated cross-coupling strategies. As the communication between the bimesityl core and the anchored anthracenes is negligible or only marginal, the trends observed for luminescence of model constituent anthracenes are reproduced in the condensed-phase photoluminescence and electroluminescence of 1-7. In other words, the emission characteristics, i.e., lambda(max) and quantum yields, are readily modulated via appropriate modification of the fluorophores. The functional behavior of this unique class of amorphous materials based on the bimesityl scaffold is demonstrated by fabrication of OLED devices. The 2-fold functionalized derivatives 1 and 2 lend themselves to sublimation techniques, so that the electroluminescence is captured with high efficiencies at low turn-on voltages (3.5-6.5 V). The device ITO/NPB (400 A)/1% 2:MADN (400 A)/TPBI (400 A)/LiF (10 A)/Al (1500 A) for 2 yields the highest luminance of approximately 13,900 cd/m(2) at 17.5 V, a maximum luminance efficiency of approximately 7.4 cd/A at 4.5 V, and a power efficiency of approximately 5.3 lm/W at 4.0 V. Further, at a brightness of 800 cd/m(2) and a current density of 13.8 mA/cm(2), the device is found to exhibit excellent luminance efficiency of 5.8 cd/A, external quantum efficiency of 4.3% with a power efficiency of 2.2 lm/W, and pure blue light with a CIE(x,y) (x = 0.13, y = 0.18). The performance characteristics of the devices fabricated for 1 and 2 are remarkable. Although the 4-fold functionalized systems did not permit sublimation leading to spin-coating as a means for device fabrication, the observed electroluminescence for 4 and 5 attests to a broader scope and applicability of this new category of amorphous molecules for application in OLEDs.