Donor-bridge-acceptor triads consisting of the Alq3 complex, oligofluorene bridge, and PtII tetraphenylporphyrin (PtTPP) were synthesized. The triads were designed to study the energy level/distance-dependence in energy transfer both in a solution and in solid state. The materials show effective singlet transfer from the Alq3-fluorene fluorophore to the porphyrin, while the triplet energy transfer, owing to the shorter delocalization of triplet excitons, appears to take place via a triplet energy cascade. Using femtosecond transient spectroscopy, the rate of the singlet-singlet energy transfer was determined. The exponential dependence of the donor-acceptor distance and the respective energy transfer rates of 7.1 x 1010 to 1.0 x 109 s-1 with the attenuation factor â of 0.21 +/- 0.02 A-1 suggest that the energy transfer proceeds via a mixed incohererent wire/superexchange mechanism. In the OLEDs fabricated using the Alq3-oligofluorene-PtTPP triads with better triplet level alignment, the order of a magnitude increase in efficacy appears to be due to facile triplet energy transfer. The devices, where the triplet-triplet energy transfer is of paramount importance, showed high color purity emission (CIE X,Y: 0.706, 0.277), which is almost identical to the emission from thin films. Most importantly, we believe that the design principles demonstrated above are general and may be used to prepare OLED materials with enhanced quantum efficacy at lowered operational potentials, being crucial for improved lifespan of OLEDs.

A series of unsymmetrical thiophene diols has been prepared in two steps from thiophene in 16-46 % yields. The unsymmetrical thiophene diols containing functionalised aryl groups were then used as key synthons for the synthesis of a series of monofunctionalised 21-thia (N 3 S), 21,23-dithia (N 2 S 2 ) and 21-thia-23-oxaporphyrins (N 2 SO). Condensation of one equivalent of unsymmetrical diol with either two equivalents of aldehyde and three equivalents of pyrrole, one equivalent of symmetrical 16-thiatripyrrane or one equivalent of symmetrical 16-oxatripyrrane under standard porphyrin-forming conditions resulted in monofunctionalised 21-

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