Supramolecular Zinc Phthalocyanine–Imidazolyl Perylenediimide Dyad and Triad: Synthesis,Complexation, and Photophysical Studies

Two new supramolecular architectures based on zinc phthalocyanine (Pc) and imidazolyl‐substituted perylenediimide (PDI), ZnPc/DImPDI/ZnPc 1 and ZnPc/ImPDI 2 , have been prepared. A strong electron‐donor, 8 , which contained eight tert‐octylphenoxy groups was synthesized to ensure high solubility, thereby reducing aggregation in solution and providing σ‐donor features while avoiding regioisomeric mixtures. Also, PDI units were functionalized with tert‐octylphenoxy groups at the bay positions, which provide solubility to avoid aggregation in solution, together with one and two imidazole moieties in the amide position, 6 and 4 , respectively, to be able to strongly coordinate with the ZnPc complex. Supramolecular complexation studies by ¹H NMR spectroscopy and ESI‐MS demonstrate a high coordinative binding constant between imidazole‐substituted 4 or 6 and 8 . The same results were confirmed by UV/Vis and fluorescence titration studies. UV/Vis titration studies revealed the formation of a 1:1 complex ZnPc/ImPDI 2 for the systems 8 and 6 and a 2:1 complex ZnPc/DImPDI/ZnPc 1 for the interaction of 8 and 4 . The binding constant in both cases was determined to be on the order of 10⁵ M ⁻¹. Femtosecond laser flash photolysis measurements provided a direct proof of the charge‐separated state within both supramolecular assemblies by observing the transient absorption band at 820 nm due to the zinc phthalocyanine radical cation. The lifetimes of charge‐separated states are (9.8±3) ns for triad 1 and (3±1) ns for dyad 2 . As far as we know, this is the first time that a radical ion pair has been detected in a supramolecular assembled ZnPc–PDI system and has obtained the longest lifetime of a charge‐separated state published for ZnPc–PDI assemblies.     

Characterization and Polymerization of Thienylphenyl and Selenylphenyl Amines and Their Interaction with CdSe Quantum Dots

Hybrid quantum‐dot‐sensitized solar cells show promising novel optoelectronic properties. An adequate design of such cells requires a deep understanding of the characteristics of each component, including their interactions. In this context, the electrochemical properties of two different hole‐transporting materials (HTMs) and their chemical interactions with trioctylphosphine‐capped CdSe quantum dots are investigated to evaluate their potential use in hybrid quantum‐dot‐sensitized solar cells. Tris[4‐(thien‐2‐yl)phenyl]amine (TTPA) and tris[4‐(selen‐2‐yl)phenyl]amine (TSePA) are studied in the solid state as thin films deposited on a conducting substrate. Spectroelectrochemical studies evidence both solid‐state electropolymerization and doping. Upon addition of TSePA or partially polymerized TTPA to a colloidal solution of trioctylphosphine‐capped CdSe quantum dots, the steady‐state photoluminescence is quenched. This suggests that the quantum dots and the HTM strongly interact, probably through an excited‐state charge‐transfer mechanism. The combination of all these pieces of information indicates that polymerized TTPA and TSePA are potential candidates as HTMs for hybrid quantum‐dot‐sensitized solar cells.     

Ammonia IRMS-TPD measurements on Brønsted acidity of proton-formed SAPO-34

By utilizing the advantages of a combined method of IRMS-TPD of ammonia and DFT calculations, the solid acidity of HSAPO-34 was studied. The number, strength and structure of the Br?nsted OH were measured experimentally. The quantitative measurements and DFT calculations supported the identification of Br?nsted OH to account for the generation model of the Br?nsted OH primarily located in the edge of the Si domain (island). The acid strength of SAPO-34 was slightly weaker than that of chabazite, a zeolite with the same structure. Thus, some important insights were obtained to understand the acid site generation of SAPO-34.     

Application of Laguerre matrix polynomials to the numerical inversion of Laplace transforms of matrix functions

This paper presents an application of Laguerre matrix polynomial series to the numerical inversion of Laplace transforms of matrix functions.     

Light‐Harvesting Phthalocyanine–Diketopyrrolopyrrole Derivatives: Synthesis,Spectroscopic, Electrochemical,and Photochemical Studies

A new family of light‐harvesting zinc phthalocyanine (ZnPc)–diketopyrrolopyrrole (DPP) hybrids have been synthesized and characterized. The absorption spectral measurements showed that the major absorptions of DPP (450–600 nm) are complementary to those of zinc phthalocyanine (300–400 and 600–700 nm). Therefore, the designed hybrids absorb over a broad range in the visible region. The geometric and electronic structures of the dyads were probed by initio B3LYP/6‐311G methods. The majority of the HOMOs were found to be located on the ZnPc, while the majority of the LUMOs were on the DPP units. The DPP units serve as the antenna, which upon excitation undergo efficient singlet–singlet energy transfer to the attached ZnPc units. The formed singlet ZnPc, in turn, donates its electron to the electron‐deficient DPP forming the low‐lying radical ion pairs ZnPc^.+–DPP^.? (energy=1.44–1.56 eV as calculated from the electrochemical measurements). The excited‐state events were confirmed by using a transient absorption technique in the picosecond–microsecond time range, as well as a time‐resolved emission technique. The rates of energy transfer from the singlet DPP to ZnPc were found to be extremely fast >10¹⁰ s^?1, while the rates of electron transfer from the singlet excited state of ZnPc to DPP were found to be 3.7–6.6×10⁹ s^?1.     

Dispersive solid-state dye laser oscillators

Narrow-linewidth multiple-prism grating solid-state dye laser oscillators are analysed using ray transfer matrices. Attention is given to beam divergence measurements and the effect on them of thermal lensing, at the solid-state gain medium. It is found that although thermal lensing leads to an increment of beam divergence, it induces oscillation in the unstable resonator regime, thus contributing to the attainment of TEM00 beam profiles. In addition, narrow-linewidth emission in dispersive oscillators, incorporating rhodamine 6 G doped HEMA:MMA gain media, is reported for the first time. Laser efficiency is 4–5% at a laser linewidth ≤1.8 GHz for double-longitudinal-mode emission. Beam divergence is measured in the 2–2.3 mrad range, in good agreement with theory. This revised version was published online in November 2006 with corrections to the Cover Date.     

Comparative study between IR and UV laser radiation applied to the removal of graffitis on urban buildings

The present article focuses on a comparison between cleaning process of graffitis on urban buildings by using laser radiation at 308 nm (XeCl excimer laser) and 1064 nm (Nd:YAG laser). Laser-induced breakdown spectroscopy (LIBS) elemental analysis was applied as real-time diagnostic technique, safeguarding against possible damage of the substrate during ablation rate studies. The morphological analysis of the etched surfaces by optical microscopy and environmental scanning electron microscopy reveals remarkable features of interest to understand the wavelength dependence of the ablation efficiency. The ablation threshold fluences of different paints sprayed on several substrates were determined applying a photoacoustic technique. To remove graffitis from urban buildings the laser radiation at 1064 nm was observed to be the most efficient wavelength, supporting the best result.     

Photophysical and lasing properties of pyrromethene 567 dye in solid poly(trifluoromethyl methacrylate) matrices with different degrees of crosslinking

The effect of increasing the rigidity of the host matrix by controlled crosslinking of the polymeric chains on the lasing and photophysical properties of pyrromethene 567 (PM567) was evaluated. To this end, the dye was dissolved in 2,2,2-trifluoromethyl methacrylate (TFMA) together with different amounts of the crosslinking monomer ethylene glycol dimethacrylate (EGDMA). Increasing the concentration of this crosslinker monomer resulted in significant increases in both lasing efficiency and photostability. Good correlation between fluorescence and lasing properties has been observed, indicating the existence of an optimum degree of crosslinking for which lasing efficiency and photostabilty reach their highest values. These new solid materials show lasing efficiencies up to 18% when transversely pumped at 534 nm and good photostabilities, with a decrease in the initial laser output of 45% after 10000 pump pulses. Received: 16 February 2001 / Revised version: 9 April 2001 / Published online: 8 June 2001     

The protonation constant of triethanolamine in KBr and KNO3 solutions at 25°C

We determined the stoichiometric acid-base constants of triethanolamine at 25°C in KBr and KNO₃ at different ionic strengths by the potentiometric technique using glass electrodes sensitive to the H⁺ ion. By applying the Pitzer equations for the activity coefficients of the species present in the medium we obtained equations accounting for the dependency of pK on the ionic strength. The coefficients thus obtained are critically analyzed.     

Studies on laser action from polymeric matrices doped with coumarin 503

Received: 20 December 1997/Revised version: 10 February 1998