A fluorene-bridged squaraine dimer (SD-FLU-SD) was designed with the purpose of combining various chromophores in one molecule and enhancing its two-photon absorption properties using intra-and interchromophore transitions. Linear and nonlinear absorption properties of SD-FLU-SD were investigated with the goals of understanding the nature of one-and two-photon absorption spectra, determining the molecular optical parameters, and performing modeling of the photophysical processes. The optical behavior of this new SD-FLU-SD "hybrid" molecule was compared with its separate squaraine constituent moiety. Linear spectroscopic characterization includes absorption, fluorescence, excitation and emission anisotropy, and quantum yield measurements in solvents of different polarity and viscosity. Spectral positions of the absorption−fluorescence peaks and quantum yields of SD-FLU-SD and its separate squaraine moiety exhibited complex and nontrivial behavior as a function of solvent polarity. Comprehensive study of this unusual solvatochromism was conducted and interpreted using various models. Nonlinear spectroscopic studies included two-photon absorption measurements using the femtosecond Z-scan technique. The two-photon absorption spectrum of SD-FLU-SD was broad, covering the spectral range from 800 to 1400 nm with a maximum two-photon absorption cross section of 2 750 GM (1 GM = 1 × 10 −50 cm 4 s/photon). Quantum chemical analysis, based on time-dependent density functional theory, agreed with the experimental data and revealed details on the energy-level structure and origin of the linear and nonlinear absorption behavior of this novel SD-FLU-SD compound. These investigations advance the understanding of the nature of electronic transitions and the structure−property relations in long conjugated molecules, which are important for the rational design of new organic optical materials.

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Parkinsonian patients may have symptoms consistent with intestinal pseudo-obstruction, but a primary intestinal abnormality has not been shown. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), after conversion to a toxic metabolite via the monoamine oxidase system, can induce Parkinson's disease by destroying dopaminergic neurons in the substantia nigra in humans and primates. Rodents have some catecholamine depletion but much less so than primates. Using chronic bipolar electrodes on the proximal jejunum of Wistar rats, we show significant, chronic migrating myoelectric complex disruption (P less than 0.001) and prolongation of irregular spike activity (P less than 0.001). Pargyline (a monoamine oxidase inhibitor) pretreatment significantly blocked these myoelectric changes. Sinemet (L-dopa and carbidopa), given after MPTP to replete dopamine, decreased the MPTP-induced migrating myoelectric complex disruption. Jejunal myenteric plexus dopamine levels were significantly decreased (to 61% of control) after MPTP but after much higher doses than were required to disrupt migrating myoelectric complex activity (180 mg/kg total vs. 30 mg/kg). Dopamine in the central nervous system was not depleted. We conclude that MPTP causes intestinal myoelectric disruption (which can be blocked by pargyline and decreased by Sinemet) possibly through enteric, but not central, nervous system effects.

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Two indole-based squaraine dyes, bearing two pyrenyl groups through vinyl or ethynyl linkers, were synthesized with the aim of enhancing the intramolecular charge transfer interaction in addition to improving their optical properties. The absorption and emission properties of these derivatives were determined to gain insight into the intensity of this type of interaction, their aggregation behavior, and for comparison with results obtained through quantum chemical calculations. Both compounds exhibited high photochemical stability, high molar absorptivity, large fluorescence quantum yields, and relatively low tendency of forming excimers in several solvents. Nonlinear spectroscopic studies revealed two-photon absorption (2PA) cross section maxima greater than 10 000 GM (1 GM = 1 × 10–50 cm4 s/photon), which are higher values relative to the indole-based squaraine core. Experimental results were compared with time-dependent DFT calculations. These observations contribute to the study of intramolecular charge transfer interaction, and its tailoring for the improvement of linear and nonlinear optical properties as well as suggests a paradigm in the construct of highly absorbing organic molecules containing pyrenyl groups for the development of new photonics materials.