We investigated on cyanine dye (HQ) in Langmuir and Langmuir-Blodgett (LB) films using UV-visible spectra and second-harmonic generation (SHG) methods. UV-visible spectra indicated a uniform film transfer. The significant SHG fringe signal as a function of angle of incidence for Z-type LB films observed respectively. The second-order susceptibility χ(2)zzz, refractive indexes at 532 nm as well as the average tilt angle ψ between the molecular (dipolar) axis and surface normal, obtained by means of fitting the SHG data, are 42 pM/V-1, 1.4841, 57° and 32 pM/V-1, 1.4775, 53° for LB films without and with Cd2+ ions, respectively. These high nonlinearities are due to resonant enhancement resulting from the proximity of the second harmonic wavelength to the absorption band of the films.
We investigated on cyanine dye (HQ) in Langmuir and Langmuir-Blodgett (LB) films by surface pressure-area (π-A)
isotherms, UV-visible and polarized UV-visible spectra as well as small angle x-ray diffraction (SAXD) measurement.
It is found from the isotherms that there is a critical point on Langmuir films near the area 0.8nm2/molecule for HQ LB
films with and without Cd2+ ions respectively and suggested that the facts should result from the phase transition due to
the change of molecular tilt angle on surface of sub-phase. UV-visible spectra indicated a uniform film transfer. The
orientation angle of HQ molecular chromophore in LB films was measured by polarized UV-visible absorption spectra,
and the result showed that the angle with respect to the substrate surface was 65 and 59 degree without and with Cd2+
ions respectively, which are agreement with those obtained from the surface pressure-area isotherm. It is suggested that
the arrangements of the HQ molecule in LB films incorporating Cd2+ ions was more compact than those without Cd2+.
A novel cyanine-fullerene dyad is used as active layer in a heterostructure photovoltaic cell based on PEDOT and buckminsterfullerene C60. The photocurrent spectrum of the device matches the absorption spectrum of the film and shows monochromatic quantum efficiencies of 5.5% and fill factors above 0.35 at white light irradiation intensities up to 310 mW/cm2. By blending a long wavelength absorbing cyanine with the dyad, the photocurrent spectrum extends to 800 nm with appreciable monochromatic quantum efficiency. Sensitization by cyanine dyes demonstrates the possibility to achieve photovoltaic response in the near infrared.
A novel naphthalimide dimer tethered by photochtomic bisthienylethene-bridge was syhthesized by Suzuki coupling method as potentially all photo-mode memory media and fluorescent molecular switch. Bisthienylethene-bridged
naphthalimide (BTE-NP) dimer reversibly changed the fluorescence intensity by alterative irradiation with ultraviolet and green visible light probably due to the fluorescence resonance energy transfer (FRET) from naphthalimides to the closed form of bisthienylethene moiety. All compounds were characterized by 1H NMR spectra and mass spectra etc. The spectroscopic properties including the fluorescence lifetime and photochromic quantum yields of BTE-NP were also measured.
A fluorene derivative having two diarylethene units at the 9,9'-positions was synthesized, and the photochromic behavior was examined in solution. Upon irradiation with UV (240nm), the solution of the diarylethene dimer turned yellow. It can returned to ring-open form upon irradiation with visible light (405nm). Two diarylethene chromophores are connected to the fluorene without π-conjugation between them in the dimer. Its synthesis can be performed on a large scale from cheap commercial products and no expensive drugs were concerned in the synthetic route.
Organic light emitting diodes (OLED) employing an Ir complex with coumarin (C6) and acetylacetone (acac) ligands Ir(C6)2(acac) are studied. This novel Ir complex can be used both as electron transporting material and light emitting dopant. From a calculation, the PL quantum efficiency of Ir(C6)2(acac) in dilute chloroform solution is 70%. With a device structure of ITO (indium tin oxide)/T-NATA(4,4’,4"-tris(N-(2-Naphthyl)-N-phenyl-amino)triphenylamine)(40nm)/NPB(N,N’-bis(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’diamine)(40nm)/Alq3(tris-(8-hydroxy-quinoline)aluminum):Ir(C6)2(acac)(1%)(40nm)/Alq3(tris-(8-hydroxy-quinoline)aluminum)(40nm)/LiF(Lithium fluoride)(1nm)/Al
(120nm), a green color (CIE coordinates x=0.22; y=0.65) and a max luminance of 33792 cd/m2 and an efficiency of 12cd/A are obtained. The solid film of Ir(C6)2(acac) excited at 400 nm shows a strong orange PL emission with a peak at 562 nm. This means When C6 is coordinated with Ir metal; the concentration quench is significantly prevented. As a result, even J is high to 200mA/cm2, the device with a structure of ITO/T-NATA/NPB/Alq3:Ir (C6)2(acac)(1%)/Alq3 (40nm)/ LiF/Al can maintain the high efficiency (11.9cd/A) and the high luminance (23683 cd/m2).
This paper presents a novel series of dendrimers containing perylene diimide cores, Fréchet-type poly(arylether) dendrons, and peripheral functional units such as hole-transporting groups (carbazole) via a convergent synthetic approach with three generation. The higher generation dendrimer has an obvious site-isolation effect or dilution effect of dendrons, which results in a relatively small red-shift of absorption and emission spectra when they form a solid thin film for applications. The interactions between peripheral units and perylene diimide core in the dendrimers are studied by fluorescence spectra. The steady-state fluorescence shows there is no effective Förster intramolecular energy transfer. DSC results indicate that the incorporation of Fréchet-type poly(arylether) dendrons can improve the amorphous property and increase glass transition temperature (Tg). The preliminary EL results with a single-layer architecture demonstrate that these dendrimers could be utilized as a promising kind of active red luminescent emitters.
Two bisindolylmaleimide derivatives were prepared in good yields, characterized and successfully employed in the fabrication of organic light-emitting-diodes (OLEDs). The absorption spectra and photoluminescence spectra of the compounds in solution and in thin film were also measured and they show larger Stokes shifts (>100nm). With the electroluminescence devices configured as ITO/NPB/dopant:Alq3 /Alq3/LiF/Al, they exhibit yellow (A) and orange (B) color. In particularly, the two devices can be turned on at 5.2 V (device A) and 5.9V (device B), and reached the maximum brightness of 15066 and 8593cd/m2 at 21V, respectively. From the cyclic voltammetry and the onset absorption, the highest occupied molecule orbital (HOMO) and the lowest unoccupied molecule orbital (LUMO) energy levels can be estimated as A (5.3, 2.9eV) and B (5.4, 3.1eV).
Some novel 2, 5, 9, 12- tetra-substituted quinacridones were synthesized. The comparison of absorption spectra and fluorescence spectra of these soluble quinacridones between in solutions and in solid film indicated that the formation of intermolecular hydrogen bonds in the crystalline was obstructed by N-alkylation. These compounds have good solubility in common solvents such as dichloromethane, chloroform, acetone, DMF etc. The good solubility provides an opportunity for a higher doping concentration of the quinacridone fluorophore chromophore in the application of photoelectronic devices. The longer fluorescence lifetimes (ca. 20 ns) of these soluble quinacridones were measured by single-photon counting technique, which seems to be hopeful for the luminescence application. The EL device made with the soluble quinacridone show a luminance of 150 cd/m2 and injected current as high as 400 mA/ cm2 at 18 V.
A series of naphthalimides containing schiff base moiety were prepared by condensation of 4-hydrazino-1,8-naphtahlimides with subsititued formaldehyde. Electronic interaction between the 4-amino-1,8-naphthalimide and the substitutent moiety results in red shift of the absorption and fluorescence maximum wavelengths in the acetonitrile solution and in the solid state. Some of these dyes emit brilliant red fluorescence in the solid state.
With the development made by Graetzel et al on solar cell, the studies on dye-sensitized nanocrystalline TiO2 solar cell have been widely investigated. Here we synthesized four cyanine dyes containing carboxyl group. The absorption spectra and fluorescent spectra of the dyes in solution and in adsorbed state on the surface semiconductor were measured. These dyes have high absorption coefficient (~10 5M-1 cm-1), which is a major factor that affects the conversion efficiency of the solar cell. These cyanine dyes were used to sensitize nanocrystalline TiO2, and the photoelectrochemical properties of the electrodes sensitized by these cyanine dyes were measured. From the absorption spectra of the electrode it can be seen that these dyes have been efficiently adsorbed on nanocrystalline TiO2. The maximum IPCE values of dye CY-1, CY-2, CY-3 and CY-4 were 42%, 51.8%, 75.9% and 22.2% respectively. The results show that cyanine dye derivatives are promising sensitizers for nanocrystalline solar cell.
Novel bisthienylethene-based photochromic material (TAP-BTE), in which four bisthienylethenes link on the ring of tetraazaporphyrin, has been synthesized. This kind of macrocyclic-linked bisthienylethenes has demonstrated better ring-closing quantum yield and has higher absorption cross- sections (1.65 X 104 M-1cm-1). The optical switch and fatigue resistance properties of the novel photochromic material have been investigated. The results showed that TAP-BTE has a thermally gated reactivity, and is useful for non-destructive readout when it is used as the memory medium.
Subphthalocyanines (SubPc) are composed of three isoindole units containing boron inside, which defines a molecular axis and forms a cone-shaped structure. Despite being non-planar, they show a delocalized 14(pi) -electron system similar to that present in phthalocyanines. The attractive characteristics of SubPc are their chemical stability and thermal stability. We report here the synthesis of three SubPc compounds, in which the axial substituent is a bromide. The peripheral substituent in the compounds leads to an improved solubility in common organic solvents. The results demonstrated that SubPc showed a strong and broad absorption region near 600 nm. This is advantageous for the purification and important for the applications in optical storage (DVD-R).
A cyanine-in-polymer film was prepared by spin-coating process on pregrooved polycarbonate substrate, and its optical storage performance was studied. The reflectance and absorbance of the film at 830 nm wavelength are high enough for optical storage. With optimum recording condition, 58 dB of carrier-to-noise ratio was obtained for single layer disk. Both of carrier-to-noise ratio and carrier signal level are proportional to log of the reflectivity change of the film before and after laser recording.
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