| Due to the unique advantages of the organic light-emitting materials, it has attracted a great deal of research attention. Now luminescent efficiency and life time are still the thresholds that prevent the materials from practical usage. Molecular design can solve both the problems which have been testified by a lot of research works. By molecular design, the orientation of chromophores and interaction of dipole between chromophores can be controlled to get high luminescent efficiency. Meanwhile, materials with high-Tg can also be obtained by molecular designing to extend the life-time of devices. To get light-emitting materials with high synthetic characteristics, here we attempt to combine both the designing thoughts: using the oligo(phenylenevinylene)(OPV) derivatives which show high luminescent efficiency in solution as chromophores and using criss-cross structural biphenyl as criss-cross core to prevent the chromophores aggregation and using 9-ethyl carbazole, 1,3,5-trimethoxylphenyl and 9-anthracene as peripheral substituents to get higher 7g.In this paper, we have synthesized the 2, 5, 2', 5'-teramethylbiphenyl by Yamamoto coupling reaction, and the substituents in 2, 2'-position prevent the biphenyl from inter-rotation, which force the whole molecule to be criss-cross structure. Using the criss-cross structure as molecular core, we synthesized compound 1a-e by Wittig and modified Wittig-Horner reaction.Theoretical calculations have demonstrated that different peripheral substituent with different volume all can keep the two OPV branches in criss-cross configuration, and effectively inhibit the transition dipole coupling between chromophores in each branch. At the same time such a configuration bestews the molecule with amorphous solid, which is help to get high-efficiency luminescent. When the volume ofperipheral substituents becomes larger enough, the connection style and rigidity affect the configuration greatly, thereby affect the fluorescence properties. This finding provides a new research topic and sheds new light to molecular design of this materials family. Uv-vis spectra characterization indicates that the push-pull properties of peripheral sustituents can modify the energy gap (Eg) and emission color of the OPVs with 2, 5, 2',5'-terasustituent biphenyl as rigid core. The Eg of le and la are 3.105 and 2.737eV, and emission colors are blue and green respectively.Compound la displays the same absorption characteristics in the solution of concentration of lO^mol/L as in dilute solution, which suggests no obvious aggregation between the OPV molecular chromophores in the high concentration. Its fluorescence quantum yield is 41%, and its linear analog is 28% in the same condition. Its Uv-vis spectra in solid film is similar to that in toluene solution, and no obvious changes have been observed after annealing for 4hr in 100°C, because of the inhibiting of the criss-cross molecular core to the chormophore aggregation. The TGA and DSC measurement results showed that compound la has good thermostability, and its weight-loss temperature begins at 295.5°C, and the Tg is 167.8°C.In a lO^mol/L toluene solution, when excited by laser pules of 810nm, the two-photon absorption (TPA) cross-section (a) of the linear analog of la is 458.3;While the a of la is up to 1197.4, which is 2.6 times of its linear analog. As far as our knowledge, la is in the list of TPA materials with high a value. The two-photon action absorption cross-section of la is 3.6 times of its linear analog, which is obvious larger than the linear addition of the linear analog. Hereinbefore the designing stategy of this criss-cross structure acting as the molecular core proves to be feasible to explore new two-photon absorption materials, and provide a new way to design andsynthesize new type of TPA material with large a value.The research results stated above demonstrate that our molecular designing issuccessful. |
PDF Full Text Request