Two-photon absorption cross sections delta and solvatochromic properties were determined for a series of quadrupolar and dipolar compounds by using femtosecond excitation in the spectral range between 710 and 960 nm. The compounds investigated were distyrylbenzenes and polyenes bearing appropriate pi or sigma acceptors. The delta values for the centrosymmetric compounds trans, trans- 1,4-bis[2-(2',5'-dihexyloxy)phenylethenyl]-2,3,5,6-tetrafluorobenzene (6), trans, trans-1,4-bis[2-(4'-dibutylamino)phenylethenyl]- 2,3,5,6-tetrafluorobenzene (2), trans, trans-1,4-bis[2-(4'dimethylamino)phenylbutadienyl]- 2,3,5,6-tetrafluorobenzene (7), trans,-trans-1,4-bis[2-(4'-dimethylamino)phenylethenyl]2,5- dicyanobenzene (4) and trans,trans-1,4-bis[2-(4'-dimethylamino)phenylethenyl]-2- propylsulfonyl-5-(2-ethylhexyl)sulfonylbenzene (3) are on the order of 600, 1400, 1700, 3000, and 4100 x 10(-50) cm4 s photon-1, respectively. The corresponding dipolar compounds trans-2-(4'- dimethylaminophenyl)ethenyl-2,3,4,5,6-pentafluorobene (8), trans-4-(4'-dimethylaminophenyl)butadienyl-2,3,4,5,6-pentafluorobenzene (9), trans-6-(4'-dimethylaminophenyl)hexatrienyl-2,3,4,5,6- pentafluorobenzene (10) were additionally investigated. All centrosymmtric compounds are good fluorescent materials, while the dipolar chromophores 8-10 exhibit low fluorescence quantum yields. Solvatochromism was also observed for the fluorophores 2-10 as a result of intramolecular charge transfer (ICT). Furthermore, a reasonable correlation was obtained between measured and calculated delta. Quantum chemical calculations were performed by using the INDO Hamiltonian with a MRDCI scheme. The results show that the sum over states (SOS) expression for the second hyperpolarizability gamma is appropriate to describe the mechanism of two-photon absorption. Mechanistic investigations of quadrupolar compounds showed that the energy of the two-photon excited state is higher than S1.

Several substituted oligophenylenevinylenes were synthesized using the Wittig−Horner−Emmons reaction to produce the trans isomers. Optical properties of these compounds were evaluated using absorption and steady-state fluorescence spectroscopy. Fluorescence quantum yields, Φf, decrease with increasing solvent polarity and approach unity in nonpolar solvents in the case of substituted trans,trans-1,4-bis[2-(2‘,5‘-difluoro)phenylethenyl]benzenes and trans,trans-1,4-bis[2-(2‘,5‘-dialkoxy)phenylethenyl)-2,3,5,6-tetrafluorobenzenes. The compounds show a strong solvatochromic shift as a function of solvent polarity, yielding a slope of −13 300 cm- 1 according to the Lippert−Mataga equation and indicating the emission of an additional charge-transfer species. A two-state reaction model was confirmed for trans,trans-1,4-bis[2-(2‘,5‘-dialkoxy)phenylethenyl)-2,3,5,6-tetrafluorobenzene (6d) in different solvents by time-correlated single-photon counting using global analysis. A dependence of the kinetic data on solvent polarity was found (global fitted decay times in picoseconds for τ1 and τ2:  381/1281 in n-hexane; 101/1590 in toluene; 27/2974 in acetonitrile). Investigations of the solid state showed liquid crystalline behavior for 6d and for trans,trans-1,4-bis[2-(2‘,5‘-difluoro)phenylethenyl]-2,5-diheptyloxybenzene (3b). This was confirmed by polarization microscopy and thermal analysis. Both the long alkoxy chains and fluorine substitution are responsible for the formation of mesophases. Photoluminescence studies of 3b and 6d in the solid state indicated an intense emission that was yellow for 3b.

Three fluorine-containing polymers, poly(2-fluoro-1,4-phenylene vinylene), poly(2,5-difluoro-1,4-phenylene vinylene), and poly(2[5]-(n-hexyloxy)-5[2]-fluoro-1,4-phenylene vinylene) (1-3, respectively) have been synthesized by the soluble precursor method and were used to fabricate light emitting diode (LED) devices. Monosubstituted 1 yielded an electroluminescent emission peaking at 560 nm (greenyellow); polymers 2 and 3 emitted in the 600-610 nm region (red). The result for 1 represents a blue shift in emission relative to emission from hompolymeric unsubstituted poly(1,4-phenylene vinylene) (PPV) LEDs fabricated by similar techniques, while the results for 2 and 3 represent a substantial red shift. These results may be compared to those obtained from LEDs fabricated from copolymers of PPV and poly(2,3,5,6-tetrafluoro-1,4-phenylene vinylene), which show a slightly blue shifted emission relative to homopolymeric PPV (Benjamin, I.; Faraggi, E. Z.; Avny, Y.; Davidov, D.; Neumann, R. Chem. Mater. 1996, 8, 352). The qualitative difference in EL emission for this work compared to that of Benjamin et al. is attributed to the fact that EL emission from 1-3 reflects the electronic effects of fluorine substitution upon the EL spectra, whereas the work of Benjamin et al. demonstrated the effects of changes in the average chain length of EL emitting homo-PPV blocks in PPV-co-PPVF4 copolymers.

The “push−pull” electronically substituted systems poly(2[5]-chloro-5[2]-(n-hexyloxy)-1,4-phenylenevinylene) and poly(2[5]-bromo-5[2]-(n-hexyloxy)-1,4-phenylenevinylene)1 and 2, respectivelywere synthesized by a modified soluble precursor route. Thermal elimination of polyether precursors to 1 and 2 yields the final conjugated polymers as free-standing, flexible red films. The polyether precursors may be film-cast from methanol to make light emitting diode (LED) devices which have red light emission in the 620 nm region. The ease of synthesis and processibility of 1 and 2 make these promising candidates for red light emitting LEDs.