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A simple method for the synthesis of Nb2O5 films of thicknesses ranging from tens to several hundreds of nanometers on amorphous silicon dioxide or quartz substrates is presented. Nb2O5 films were formed by annealing the sputter deposited Nb films under an Ar flow and without oxygen plasma in a quartz tube within a furnace at 850 °C. The structural, compositional, optical, and vibrational properties were characterized by grazing incidence X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet visible spectroscopy, and Raman scattering. Each of the Nb2O5 films is polycrystalline with an orthorhombic crystal structure. We observed vibrational modes including longitudinal optical, transverse optical, and triply degenerate modes, and measured the indirect optical band gap to be ∼3.65 eV. The transmittance spectrum of the ∼20 nm thick Nb2O5 film shows over 90% transmittance below the band gap energy in the visible wavelength range and decreases to less than 20% in the ultraviolet regime. The optical properties of the films in the UV-vis range show potential applications as UV detectors.

Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC) reactivity was successfully employed to synthesize three donor-acceptor energy transfer (EnT) arrays that contain one (Dyad), three (Tetrad) and four (Pentad) 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) donors connected to a Zn-tetraphenylporphyrin acceptor via 1,2,3-triazole linkages. The photophysical properties of the three arrays, along with individual donor and acceptor chromophores, were investigated by UV-vis absorption and emission spectroscopy, fluorescence lifetimes, and density functional theory (DFT) electronic structure modeling. Comparison of the UV-vis absorption spectra and frontier molecular orbitals from DFT calculations of the three arrays with ZnTPP, ZnTTrzlP, and Trzl-BODIPY shows that the electronic structure of the chromophores is essentially unperturbed by the 1,2,3-triazole linkage. Time-dependent DFT (TDDFT) calculations on the Dyad reproduce the absorption spectra in THF and show no evidence of excited state mixing of the donor and acceptor. The BODIPY singlet excited state emission is significantly quenched in all three arrays, consistent with EnT to the porphyrin core, with efficiencies of 95.8, 97.5, and 97.2% for the Dyad, Tetrad, and Pentad, respectively. Fluorescence excitation spectra of the three arrays, measured at the porphyrin emission, mirror the absorption profile of both the porphyrin and BODIPY chromophores and are consistent with the Förster resonance energy transfer (FRET) mechanism. Applying Förster theory to the spectroscopic data of the chromophores gives EnT efficiency estimates that are in close agreement with experimental values, suggesting that the through-space mechanism plays a dominant role in the three arrays.

A new azido functionalized 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) has been synthesized to achieve spectral complementarity to a Zn(II) tetraphenylethynyl porphyrin (ZnTPEP). Mixed multilayer films were assembled on glass and quartz up to 10 bilayers thick in a layer-by-layer (LbL) fabrication process using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) to couple these two dyes together with a tris-azido linker. By varying the amount of BODIPY in the CuAAC reaction solutions for the azido linker layers, we achieve tunable doping of BODIPY within the porphyrin films. We are able to demonstrate linear film growth and determine thickness by X-ray reflectivity (XRR). XRR data indicated that lower BODIPY loading leads to higher porphyrin content and slightly thicker films. Fluorescence emission and excitation spectra of the mixed multilayer films show efficient quenching of the BODIPY singlet and enhanced ZnTPEP emission, suggesting efficient energy transfer (EnT). The ease of fabrication and tunability of these films may serve as potential light harvesting arrays for molecular-based solar cells.

Three perylene diimides (PDI) were synthesized with propargyl groups at the diimide positions to enable the fabrication of molecular multilayer thin films via sequential copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) coupling reactions in a layer-by-layer (LbL) fashion. The new PDIs with phenoxy (PhO-PDI), dodecylthiol (Thiol-PDI), and pyrrolidine (Pyrr-PDI) substituents in bay positions have optical absorption spectra that span a large portion of the visible region. Multilayer growth on 11-azidoundecylsiloxane coated silica glass and indium tin oxide (ITO) surfaces was demonstrated up to 10 bilayers of each PDI with 1,3,5-tris(azidomethyl)-benzene (N3Mest) via optical and infrared spectroscopy. Polarized UV-visible absorption measurements showed a strong dependence on the orientation of the film in the light path and was consistent with a preferential orientation of the PDI molecules in the film at 40–42° with respect to the substrate surface. Grazing-angle attenuated total reflectance (GATR) infrared spectra of the films show an increase in content of unreacted azides during multilayer growth from N3Mest as a result of the smaller molecular footprint as compared to the PDI components. Electrochemical scans of the multilayer films grown on ITO exhibited reversible two-electron reduction waves for the PDIs with linear increases in charge with bilayer growth. The electrochemically derived surface coverages of PDIs averaged 1.2–1.3 × 1014 molecules per cm2 for each layer added to the multilayer films. The flexibility of the CuAAC based LbL assembly methodology is highlighted by the assembly of a mixed multilayer film containing five layers of each PDI, resulting in a panchromatic film that is a summation of individual chromophores.