Red-shifted Absorption Spectra Research Articles

Optical Characteristics of La-Doped ZnS Thin Films Prepared by Chemical Bath Deposition

Undoped and La-doped ZnS thin films are prepared by chemical bath deposition (CBD) process through the co-precipitation reaction of inorganic precursors zinc sulfate, thiosulfate ammonia and La2O3. Composition of the films is analyzed using an energy-dispersive x-ray spectroscopy (EDS). Absorption spectra and spectral transmittances of the films are measured using a double beam UV-VIS spectrophotometer (TU-1901). It is found that significant red shifts in absorption spectra and decrease in absorptivity are obtained with increasing lanthanum. Moreover, optical transmittance is increased as La is doped, with a transmittance of more than 80% for wavelength above 360 nm in La-doped ZnS thin films. Compared to pure ZnS, the band gap decreases and flat-band potential positively shifts to quasi-metal for the La-doped ZnS. These results indicate that La-doped ZnS thin films could be valuably adopted as transparent electrodes.

Fluorinated Membrane Potential Probes

To explore the effect of fluorination on photophysical properties of membrane potential probes, we developed synthetic methods for ANEP dyes with fluorine substitutions at the donor, bridge, and acceptor sides. Fluorination on acceptor side induces red shifts in optical spectra while on donor side it induces blue shifts. The trend can be qualitatively rationalized as electron redistribution from donor in the ground state to acceptor in the excited state, and quantitatively predicted by quantum mechanical calculations using time-dependent density functional theory (TDDFT). Compared with parent ANEP dyes, fluorinated dyes generally show improved photostabilities in addition to similar fast response kinetics and high voltage sensitivities when tested in a voltage-clamped hemispherical lipid bilayer (HLB) apparatus. The characteristics of red-shifted absorption spectra, improved photostability, and high voltage sensitivity have enabled us to achieve a single trial resolution of 50 mV in two-photon imaging of cultured hippocampal neurons using 1100-1350 nm laser excitation, paving the way for in vivo imaging of spontaneous action potentials. (Supported by NIH grants EB001963).

Synthesis of Quinoxaline-Based Donor−Acceptor Narrow-Band-Gap Polymers and Their Cyclized Derivatives for Bulk-Heterojunction Polymer Solar Cell Applications

A series of narrow-band-gap donor−acceptor (D−A) conjugated polymers, with thiophene-substituted quinoxaline monomer 5,8-bis(5-bromothiophen-2-yl)-2,3-bis(5-octylthiophen-2-yl)quinoxaline (TTQx) or its cyclized phenazine derivative monomer 8,11-bis(5-bromothiophen-2-yl)-2,5-dioctyldithieno[2,3-a:3′,2′-c]phenazine (TTPz) as acceptors, were synthesized via Suzuki coupling reaction. It was found that the copolymers based on thiophene-substituted quinoxaline TTQx exhibit obviously red-shifted absorbance compared to previously reported D−A copolymers based on phenyl-substituted quinoxaline. Their analogous copolymers based on the cyclized TTPz acceptor show more pronounced red-shifted absorption spectra with a significantly decreased band gap due to the enlarged planar polycyclic aromatic ring of TTPz. Moreover, compared to the copolymers based on TTQx, the TTPz-based copolymers’ mobilities are also significantly increased due to the reduced steric hindrance and improved structural planarity among the copolymers. Bulk-heterojunction polymer solar cells based on the blends of the copolymers with a fullerene derivative as an acceptor exhibit promising performance, and the best device performance with power conversion efficiency up to 4.4% was achieved.

A sandwich anion receptor by a BODIPY dye bearing two calix[4]pyrrole units

AbstractA novel dicalix[4]pyrrolyl-substituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye I with an absorption peak at approximately 670 nm and an emission peak at about 690 nm was prepared. As an anion receptor, I displayed a red shift in absorption spectra and fluorescence quenching in varying degrees in the presence of F−, AcO−, H2PO4−, or Cl−. Compared with the parent calix[4]pyrrole, a representative anion receptor, I exhibited a stronger affinity to these anions due to the formation of a sandwich complex through multiple hydrogen-bonding interactions.

A large perturbation on geometry structures, excited state properties, charge-injection and -transporting abilities of Ir(iii) complexes by different substituents on ligands: a DFT/TDDFT study

The molecular geometries, electronic structures, photophysical properties, charge-injection and -transporting abilities of a series of Ir(III) complexes with different carrier-transporting substituents, such as carbazole, oxadiazole and dimesitylboryl groups, are investigated theoretically using density functional theory (DFT) and time-dependent DFT (TDDFT) calculations to understand the influence of these substituents on the optical and electronic properties of Ir(III) complexes and to explore how to improve the optoelectronic properties of the complexes. It is found that the introduction of substituents can stabilize both HOMOs and LUMOs and induce variations in the energy gap between HOMO and LUMO. The introduction of hole-transporting carbazole substituent induces the blue-shift of absorption spectrum and improves the hole-injection and -transporting performances of complex. The introduction of electron-transporting oxadiazole substituent and electron-accepting dimesitylboryl substituent induces the red-shift in absorption spectra of complexes, improves their charge transfer abilities and leads to the better balance between the hole- and electron-transporting abilities. Through Lewis acid/base interactions between B atom and F(-), the electronic properties of 4 show dramatic changes in the presence of F(-) and thus 4 can also be used as selective phosphorescent F(-) probe.

A Porphyrin Fused to Four Anthracenes

We have synthesized a fused tetraanthracenylporphyrin by oxidation of a meso-anthracenyl nickel(II) porphyrin with FeCl(3). This compound exhibits an intense red-shifted absorption spectrum (λ(max) = 1417 nm; ε = 1.2 × 10(5) M(-1) cm(-1)) and a small electrochemical HOMO-LUMO gap (0.61 eV). The crystal structure shows that it forms π-stacked dimers with a short Ni···Ni distance (3.32 Å).

Synthesis and Light-Emitting Properties of Solution-Processable Oligothiophenes Containing Triazole Moiety

The aromatic triazole is an interesting electron-injection/transport chromophore because it possesses high electron affinity and thermal stability. In organic lighting-emitting diodes (OLEDs), highly electron-deficient triazole (Tz) derivates have been demonstrated to have more efficient electron-transport and hole-blocking characteristics and have a higher stability to high current density than the oxadiazole derivates. In this study, we have successfully synthesized a star-shaped soluble oligomer,4-(4-butylphenyl)-3,5-bis(4-(5'-hexyl-2,2'-bithiophen-5-yl)phenyl)-4H-1,2,4-triazole(Tz-2T-Hex) via Suzuki coupling reaction. The Tz-2T-Hex shows a red-shifted UV-vis absorption spectrum than Tz-Br with a maximum at 380 nm, due to the introduction of two bithiophene units at both ends. As film, Tz-2T-Hex showed the PL maximum at 530 nm. Tz-2T-Hex emitted light of a white color with the CIE coordinates (0.32 and 0.34).

Oligothiophene Tetracyanobutadienes: Alternative Donor−Acceptor Architectures for Molecular and Polymeric Materials

Oligothiophene-substituted 1,1,4,4-tetracyanobutadienes (TCBDs) have been synthesized by [2 + 2] cycloaddition reactions between tetracyanoethylene and oligothiophene alkynes. The TCBD moiety is compared to other electron acceptors attached to dibutylterthiophene including dicyanovinyl (DCV) and tricyanovinyl (TCV). These donor−acceptor molecules (TCBD-3T, DCV-3T, and TCV-3T) show red-shifted absorption spectra relative to the unsubstituted oligothiophene as a result of intramolecular charge-transfer (ICT). Monosubstituted terthiophenes bearing the electron acceptors show both oxidation and reduction processes as characterized by cyclic voltammetry. Density functional theory (DFT) calculations are used to explain the electronic and redox properties of the materials. Electrochemical oxidation of a bis(terthienyl)-substituted TCBD molecule (3T-TCBD-3T) yields a conducting polymer exhibiting balanced ambipolar redox conduction with similar values for the oxidized and reduced states of the polymer (1 × 10−3 S...

Synthesis and properties of novel perylenetetracarboxylic diimide derivatives fused with BODIPY units

Two novel fluorescent dyes based on perylenetetracarboxylic diimde (PDI) with methylpyridine or methylquinoline group at the carbonyl position were designed and synthesized. Their structures were confirmed by 1H NMR, 13C NMR, MS, and elementary analysis. The resulted new compounds show longer wavelength absorption with relative high extinction coefficient and red-shifted emission with high fluorescence quantum yields. These compounds can further react with BF 3·Et 2O to form novel dyes containing BODIPY (difluoroboradiazaindacene) analogue unit, by which both the absorption and emission maximum have been red-shifted further. The minimized structures based on density function theory (DFT) calculation show planar configurations for the compounds. The calculated molecular orbital correlates well with their red-shifted absorption and emission spectra.

Theoretical investigation into optical and electronic properties of oligothiophene derivatives with phenyl ring as core or end-capped group in linear and V-shape

A series of thiophene-based oligomers has been designed to explore their optical, electronic, and charge transport properties for charge transport materials. These oligomers consist of oligothiophene, oligo(thienylenevinylene), and m- or p-phenyl as the core in two shapes (linear shape and V-shape). Phenyl ring as the end-capped group is also investigated in the linear shape. The DFT-PBE0/6-31G(d,p) and the TD-PBE0/6-31+G(d,p) calculated results reported herein show that the V-shape oligomers have larger HOMO-LUMO gaps because of meta-substitutions on phenyl cores, corresponding to blue shifts of absorption spectra. The linear oligomers with phenyl ring as end-capped group display red shifts of absorption spectra. The V-shape oligomers provide small reorganization energies. Our recommended polymer possessing 1,2,4-phenyl core and longer OTV side fragments is a good candidate for the design of charge transport and/or solar cell materials.

An efficient fluoroionophore for selective recognition of Hg 2+ and Cu 2+ ions

An azo-phenol based receptor 2 viz., 1-(6-nitrobenzothiazole-2-ylazo)naphthalene-2-ol has been designed, synthesized and characterized. The sensing behavior of receptor for different metal ions viz. Na +, K +, Ca 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Hg 2+, Ag + and Cd 2+ has been studied in aqueous acetonitrile solution and was found specific for both the Hg 2+ and Cu 2+ transition metal ions. The chemosensor upon interaction with Hg 2+ and Cu 2+ ions shows well defined naked-eye visible color change from a yellow-green to pink and blue respectively, with a significant red-shift in absorption spectra. The estimated association constant and, enhancement and quenching in fluorescence emission spectra respectively, reveals the affinity of chemosensor for Hg 2+ and Cu 2+ ions. The FT-IR spectral analysis have suggested the probability of complexation, in the reaction medium, between metal ions and 2, through naphthol OH, azo N and thiazole N as a potential coordination sites.

A Red-Shifted Chlorophyll

Chlorophylls are essential for light-harvesting and energy transduction in photosynthesis. Four chemically distinct varieties have been known for the past 60 years. Here we report isolation of a fifth, which we designate chlorophyll f. Its in vitro absorption (706 nanometers) and fluorescence (722 nanometers) maxima are red-shifted compared to all other chlorophylls from oxygenic phototrophs. On the basis of the optical, mass, and nuclear magnetic resonance spectra, we propose that chlorophyll f is [2-formyl]-chlorophyll a (C55H70O6N4Mg). This finding suggests that oxygenic photosynthesis can be extended further into the infrared region and may open associated bioenergy applications.

Bis-Anthracene Fused Porphyrins: Synthesis, Crystal Structure, and Near-IR Absorption

Synthesis of fused bis-anthracene porphyrin monomers and dimers has been achieved by oxidative ring closure using FeCl(3) and Sc(OTf)(3)/DDQ, respectively. The fused compounds display red-shifted absorption spectra with maxima in the near-IR at 973 and 1495 nm, respectively, and small electrochemical HOMO-LUMO gaps. The crystal structure of the fully fused bis-anthracene porphyrin shows that it has a regular planar pi-system.

Analysis of interaction between tamoxifen and ctDNA in vitro by multi-spectroscopic methods

Multi-spectroscopic methods including resonance light scattering (RLS), ultraviolet spectra (UV), fluorescence spectra, (1)H NMR spectroscopy, coupled with thermo-denaturation experiments were firstly used to study the interaction of antitumor drug tamoxifen (TMX) with calf thymus (ctDNA) in acetate buffer solutions (pH 4.55). The interaction of TMX with ctDNA could cause a significant enhancement of RLS intensity, the hyperchromic effect, red shift of absorption spectra and the fluorescence quenching of TMX, indicating that there is an inserting interaction between TMX and ctDNA. This inference was confirmed by (1)H NMR spectroscopy. The chemical shift of the benzene proton changes significantly which indicates that TMX could insert into the base pairs of ctDNA. These studies are valuable for a better understanding the mode of TMX-ctDNA interaction further, which are important and useful for designing of new ctDNA targeted drug. And the antitumor drug TMX inserted directly into ctDNA in vitro, which can provide a lot of useful information to explore the development of new and highly effective anti-cancer drugs.

Synthesis and characterization of porphyrin-terthiophene and oligothiophene π-conjugated copolymers for polymer solar cells

Two novel conjugated polymers with alternating main chain structures of zinc porphyrin-terthiophene (P-PTT) and zinc porphyrin-oligothiophene (P-POT) were synthesized by Stille reaction. The effect of different lengths of thiophene chains on the thermal, optical, electrochemical, and photovoltaic properties of the two copolymers were investigated in detail. P-PTT exhibited higher onset decomposition temperature (392 °C) and glass-transition temperature (152 °C) than those of P-POT. The introduction of thiophene units in the meso-aryl positions of porphyrin resulted in the red shift and broader absorption spectrum compared with zinc porphyrin (P Zn) monomer both in chloroform solutions and on thin solid films. The electrochemical properties indicated that the energy levels of the polymers were suitable for efficient charge transfer and separation at the interface between the polymer donor and PCBM acceptor. The bulk heterojunction solar cells based on P-PTT and P-POT showed power conversion efficiencies up to 0.32% and 0.18%, respectively.

The determination of thiols based using a probe that utilizes both an absorption red-shift and fluorescence enhancement

A pyridylvinylene derivative containing piazselenole displayed high selectivity toward glutathione in the presence of other biorelevant analytes. The compound exhibited a 19 nm red-shift in absorption spectra and ∼3-fold fluorescence intensity enhancement; in addition, it was possible to detect micromolar amounts of glutathione quantitatively using both red-shift absorbance and enhanced fluorescence. The mechanism of the reaction between the modified pyridylvinylene derivative and glutathione was confirmed using ESI-MS and absorption/fluorescence spectra.

Curcumin as a colorimetric and fluorescent chemosensor for selective recognition of fluoride ion

The binding properties of curcumin with anions in acetonitrile were examined for the first time by UV–vis absorption and fluorescence spectroscopies. The results showed that curcumin highly and selectively responded to F − over other anions such as AcO −, H 2PO 4 − and Cl − because of anionic complex formation via hydrogen bond. Curcumin gave rise to the red-shift of absorption spectra and its fluorescence was quenched with concomitant color change from yellow to purple upon addition of F −, which was detected by naked eyes. The addition of other anions such as AcO −, H 2PO 4 −, HSO 4 −, NO 3 −, Cl − and Br − did not result in observable spectral change and solution color change. The binding constant between curcumin and F − was 2.0×10 5 mol −1 L and the recognizing mechanism was investigated as well.

Synthesis, Self-Assembly and Solution-Processed Field-Effect Transistors of a Liquid Crystalline Bis(dithienothiophene) Derivative

A new liquid crystalline dithienothiophene dimer cap-functionalized with 3,4,5-tris-n-dodecyloxyphenyl groups (1) has been synthesized. The absorption spectrum blue-shifts 7 nm, while the fluorescence spectrum red-shifts 95 nm in thin film with respect to that in solution, suggesting that H-aggregate formation may occur and the molecules are cofacially aligned in the solid state. Compound 1 self-organized into highly ordered, long-range 2-dimensional nanopatterns on highly oriented pyrolytic graphite; their structures were characterized by scanning tunneling microscopy. The liquid crystalline phase was formed upon heating or cooling and was investigated using differential scanning calorimetry and polarizing optical microscopy. Thermal annealing led to a 13 nm red shift of absorption spectra of 1 in the thin film, indicating liquid crystalline enhanced ordering. Solution-processed organic field-effect transistors based on 1 exhibited a mobility of 1.7 × 10−3 cm2 V−1 s−1 and an on/off ratio of 2 × 105.

Revealing Linear Aggregates of Light Harvesting Antenna Proteins in Photosynthetic Membranes

How light energy is harvested in a natural photosynthetic membrane through energy transfer is closely related to the stoichiometry and arrangement of light harvesting antenna proteins in the membrane. The specific photosynthetic architecture facilitates a rapid and efficient energy transfer among the light harvesting proteins (LH2 and LH1) and to the reaction center. Here we report the identification of linear aggregates of light harvesting proteins, LH2, in the photosynthetic membranes under ambient conditions by using atomic force microscopy (AFM) imaging and spectroscopic analysis. Our results suggest that the light harvesting protein, LH2, can exist as linear aggregates of 4 +/- 2 proteins in the photosynthetic membranes and that the protein distributions are highly heterogeneous. In the photosynthetic membranes examined in our measurements, the ratio of the aggregated to the nonaggregated LH2 proteins is about 3:1 to 5:1 depending on the intensity of the illumination used during sample incubation and on the bacterial species. AFM images further identify that the LH2 proteins in the linear aggregates are monotonically tilted at an angle 4 +/- 2 degrees from the plane of the photosynthetic membranes. The aggregates result in red-shifted absorption and emission spectra that are measured using various mutant membranes, including an LH2 knockout, LH1 knockout, and LH2 at different population densities. Measuring the fluorescence lifetimes of purified LH2 and LH2 in membranes, we have observed that the LH2 proteins in membranes exhibit biexponential lifetime decays whereas the purified LH2 proteins gave single exponential lifetime decays. We attribute that the two lifetime components originate from the existence of both aggregated and nonaggregated LH2 proteins in the photosynthetic membranes.

Structures and excitation energies of Zn–tetraarylporphyrin analogues: A theoretical study

The photophysical properties of β-substituted Zn–tetraarylporphyrin (ZnTAP) analogues used as dyes in dye-sensitized solar cells were studied using density functional theory (DFT). Singlet-excitation energy calculations of ZnTAP analogues were performed using time-dependent DFT with B3LYP, B3PW91, PBE0 exchange–correlation functionals at 6-31G(d) and 6-31+G(d) basis sets using B3LYP/6-31G(d) geometries. The PBE0 functional at 6-31+G(d) basis set provided a better correlation with the experimental data for both B- and Q-bands. The inclusion of solvation effect in the calculations provided a good agreement in terms of B:Q ave ratio of the oscillator strengths for both analogues with the experimental values. Analogue 2 has a higher and a more balanced charge-carrier transport rates than analogue 1. In general, the addition of an electron-donating group in the meso-substituent (analogue 2) resulted in a narrower band gap, higher oscillator strength, a more red-shifted absorption spectra, and better charge-transfer characteristics than analogue 1.