Mono-and bifunctional oligo(p-phenylene vinylene)s (OPVs) functionalized with ureido-s-triazine units have been synthesized and fully characterized. In chloroform monofunctional OPV derivatives dimerize with a dimerization constant of K dim ) (2.1 ( 0.3) × 10 4 L/mol, while bifunctional OPV derivatives are present as random coil polymers in this solvent. In more apolar solvents such as dodecane, the hydrogenbonded dimers of the monofunctional OPV derivative aggregate in chiral stacks, as can be concluded from UV/vis, fluorescence and CD spectroscopy. Temperature-dependent measurements show a first-order transition at 53 ( 3 °C from the aggregated state to the molecularly dissolved phase. The bifunctional derivative also aggregates in dodecane; however, based on CD measurements, these aggregates are less organized. This behavior is presumably the outcome of a competition between favorable π-π interactions and restricted conformational freedom, due to the hexyl spacer, which results in a frustrated supramolecular polymeric stack. The length of these polymers as well as the chiral order in the assemblies can be controlled by the addition of monofunctional OPV derivatives.

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The synthesis of a homologous series of oligo(p-phenylene vinylene)-fulleropyrrolidines (OPVn-C 60 , n ) 1-4, where n is the number of phenyl rings) is described. The photophysical properties of these donoracceptor dyads and the corresponding model compounds, R,ω-dimethyl-2,5-bis(2-(S)-methylbutoxy)-1,4phenylene vinylene oligomers (OPVn, n ) 2-4) and N-methylfulleropyrrolidine (MP-C 60 ), are studied as a function of the conjugation length in solvents of different polarity and as thin films. Fast singlet energy transfer occurs after photoexcitation of the OPVn moiety of the dyads toward the fullerene moiety in an apolar solvent. Photoexcitation of the dyads in a polar solvent results in electron transfer for OPV3-C 60 and OPV4-C 60 , and to some extent for OPV2-C 60 , but not for OPV1-C 60 . These results are compared to the results obtained for mixtures of OPVn and MP-C 60 in the same solvents. The solvent-dependent change in free energy for charge separation of the donor-acceptor systems is calculated from the Weller equation, and the rate constants for energy and electron transfer are derived from the fluorescence lifetime and quenching. The results show that in a polar solvent electron transfer in these dyads is likely to occur via a two-step process, that is, a very fast singlet energy transfer prior to charge separation. In thin solid films of OPV3-C 60 and OPV4-C 60 , a long-lived charge-separated state is formed after photoexcitation. The long lifetime in the film is attributed to the migration of charges to different molecules. A flexible photovoltaic device is prepared from OPV4-C 60 .

The excited state properties of a series of ␣,-dimethyl-oligo͕2,5-bis͓2-(S)-methylbutoxy͔-p-phenylene vinylene͖s (OPVns, with n the number phenyl rings͒ are investigated for nϭ2 -7 in solution at ambient temperature, under matrix-isolated conditions at low temperature, and as nanoaggregates using absorption ͑time-resolved͒, photoluminescence, photoinduced absorption, circular dichroism, and circular polarized luminescence spectroscopies. The singlet (S 1 ←S 0 ) and triplet (T n ←T 1 ) transition energies decrease with conjugation length. For the S 1 state of OPVn the lifetime strongly decreases with chain length due to enhanced nonradiative decay and radiative decay. The increase in the nonradiative decay rate constant is much more pronounced, and as a result the photoluminescence quantum yield is less for longer oligomers. Studies at low temperature afforded spectra with well-resolved vibronic fine structure. Under these conditions the Stokes' shift is very small (р0.04 eV). The Huang-Rhys parameter and relaxation energies in the excited state associated with S 1 ←S 0 and T n ←T 1 transitions and their evolution with conjugation length have been determined via a Franck-Condon analysis of the vibronic fine structure. For OPV7, the relaxation energy of S 1 with respect to S 0 (0.165Ϯ0.02 eV) is considerably larger than for T n with respect to T 1 ͑0.03 eV͒, but the latter increases for the shorter oligomers, in contrast to the relaxation energy of S 1 . The OPVns (nу5) form nanoaggregates in polar solvents such as ethanol. The changes in absorption and emission together with a strong circular dichroism and circularly polarized emission indicate the formation of chiral H-type aggregates under these conditions.

Poly(propylene imine) dendrimers have been functionalized with π-conjugated oligo(p-phenylene vinylene)s (OPV's) through an amide linkage and are fully characterized. In solution the dendrimers behave as globular entities without specific interactions between the OPV units. The OPV dendrimers have an amphiphilic nature and self-assemble at the air−water interface forming stable monolayers in which the dendritic surfactants presumably adopt a cylindrical shape; all the OPV's are aligned perpendicular to the water surface, and the dendritic poly(propylene imine) cores face the aqueous phase. Optical spectra taken from Langmuir−Blodgett films show a small blue shift indicative of interactions between the OPV units. Spin-coated homogeneous thin films could be obtained from solutions containing dendrimers loaded with dyes. The optical properties of these films are similar to the Langmuir−Blodgett films which points to the same type of organization of the OPV's. The OPV dendrimers are effective extractants of anionic dye molecules from water to organic solvents. Ratios between dye and dendrimer can be easily tuned by varying the concentration of dye in the water layer. The host−guest assemblies show not complete energy transfer from the OPV units to the encapsulated dye molecules in solution. The energy transfer is very efficient in spin-coated films of dendrimer/dye assemblies and the emission wavelength can be adjusted by using a variety of dye molecules. The dendrimer/dye systems mix very well with poly(p-phenylene vinylene)s (PPV's) forming good quality thin films in contrast to films obtained from dye/PPV without dendrimer. The OPV units in the dendrimer act as a compatibilizer in these systems and energy transfer is observed from the organic PPV polymer to the dye. It gives the possibility of tuning the emission wavelength of the PPV thin films by using the appropriate encapsulated dye.