Diphenylamine-substituted cruciform oligo(phenylene vinylene)s: Enhanced one- and two-photon excited fluorescence in the solid state

1,4-di(4'-N,N-diphenylaminostyryl)benzene (DPA-DSB) is a well known compound with a large two-photon absorption (TPA) section and strong fluorescence in solution. However, the ease with which it crystallizes results in the formation of discontinuous crystalline phases during vacuum deposition processes, thereby greatly limiting its applicability in solid-state devices. A cruciform dimer of DPA-DSB, 2,5,2',5'-tetra(4'-N,N-diphenylaminostyryl)biphenyl (DPA-TSB) is reported, wherein two DPA-DSB molecules are linked through a central biphenyl bond. The DPA-TSB molecules take on a cruciform configuration because of the steric crowding around the central biphenyl core, which has the effect of efficiently suppressing crystalline and intermolecular interactions. ne neat DPA-TSB solid shows strong green-blue fluorescence because of both steady-state absorption as well as TPA. The DPA-TSB solid exhibits a photoluminescence (PL) efficiency (eta(solid)) of 29% and a solid-state two-photon action cross section (delta eta(solid)) of 954 GM (1 GM = 1 x 10(-50) cm(4) s photon(-1) molecule(-1)), which is much greater than for the model compound DPA-DSB (eta(solid) = 16% and delta eta(solid) = 150 GM, where delta is the TPA cross section and eta is the fluorescence quantum yield). Based on its high PL efficiency, good film-forming ability, and strong TPA, DPA-TSB seems to be a good candidate for applications in solid-state optical devices.