Design And Synthesis Of Novel Diketopyrrolo-Pyrrole-Containing Two-Photon Fluo-Rescence Chemosensors For Fluoride Anion And Fully Aromatic Conjugated Polymers With High Two-Photon Activity

Two-photon excitation and two-photon fluorescence have many advantages over the commonly used UV-visible one-photon ones, including exclusive confinement of the excitation to the focal volume with high3D resolution and reduced photobleaching and phototoxicity by virtue of the low-energy NIR excitation with greater depths of penetration. Organic conjugated molecules (small and polymeric compounds) with large two-photon absorption (2PA) cross sections have attracted considerable interests because of their significant applications in the areas of nonlinear optical materials, such as two-photon excited fluorescence microscopy, optical limiting, optical data storage,3D-microfabrication, up-conversion lasing, photodynamic cancer therapy, and two-photon fluorescent probes. It is very desirable that2PA materials not only have large2PA cross sections but also exhibite good photo-and thermal-stability and so on, moreover, the functional units that can act with analytes to induce the significant changes of emission intensity or fluorescence color are also hoped earnestly if2PA materials are used as two-photon fluorescent probes such as for fluoride anion. In this paper, three N-monoalkylated DPP (mDPP) derivatives,3,6-bis(4-chloro-/methyl-/bromo-phenyl)-2-octyl-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-diones (mDPP-Cl/mDPP-Me/mDPP-Br) were designed and synthesized, by facile one-step monoalkylation of commercially available or easy-prepared corresponding DPP derivatives. Three compounds all have high fluorescence quantum yields (O) and exhibit usable two-photon absorption cross sections (8=58-87GM). They are not only effective one-photon but also more effective two-photon fluorescence chemosensors selectively for fluoride anion. Moreover, the substituents at benzene ring, even though simple methyl, chloride and bromide, could affect the intramolecular charge transfer from the lactam N to the DPP core, and the sensing performance of mDPP to fluoride ion are in the order, mDPP-Br> mDPP-CI> mDPP-Me. Proton NMR titrations indicate that the intermolecular proton transfer between the hydrogen atom on the lactam N and the fluoride anion is the sensing origin. The stable chemical structure, small molecular size and usable Φδ in terms of femto-second laser pulses make mDPP moieties suitable for the construction of new and effective fully aromatic two-photon materials applicable in two-photon science and technology. Moreover, two DPP-based polymers, PDCZ and PDFL, with large2PA cross sections and exhibite good photo-and thermal-stability by Suzuki cross-coupling between bis-alkylDPP and two aromatic monomers, were synthesized. There are very important theoretical and practical significance for the development of two-photon science and technology.