Long-wavelength Absorbance Research Articles

Long-wavelength absorbing and mitochondria or lysosome organelle-targeting photosensitizers with flexible or rigid terminus for fluorescence imaging and high-performance photodynamic therapy

In this study, two chlorin photosensitizers (PSs) having long-wavelength absorbing (λmax 707 and 709 nm) and mitochondria or lysosome organelle-targeting abilities have been developed for use in photodynamic therapy (PDT). We simply modified two PSs, PS1 (N-propyl unit as a flexible terminus) and PS2 (N-propargyl unit as a rigid terminus), which displayed near-infrared absorption and fluorescence emission and high 1O2 quantum yield (0.720 and 0.593), indicating a suitable PS for PDT, resulting in high-performance photodynamic activity with low IC50 values (0.31–0.36 μM against A549 and HeLa cells). Importantly, PS1 and PS2 exhibited excellent mitochondrial or lysosomal organelle-targeting ability with high Pearson's correlation coefficient values (∼0.9). The excellent PDT effect of PS1 and PS2 was confirmed by fluorescence images of intracellular reactive oxygen species generation as well as live/dead staining images. Therefore, these two PSs have great potential as fluorescence imaging materials and PDT reagents.

Donor–Acceptor Structure-Dependent Electrochemiluminescence Sensor for Accurate Uranium Detection in Drinking Water

As is known to all, uranium is regarded as an important hazardous element in drinking water and extremely limited by the World Health Organization. To realize the accurate monitoring of uranyl in drinking water, an efficient strategy for designing an electrochemiluminescence (ECL) sensor with a low ECL potential as well as high sensitivity and selectivity is reported in this work. In detail, a donor–acceptor type structure is built in polymer dots (Pdots) to obtain a low ECL potential and long-wavelength absorbance waves to give a resonance energy transfer process from uranyl to Pdots, which is beneficial for developing a uranyl ECL sensor with high sensitivity and selectivity. The obtained Pdots are modified with ssDNA chains to be prepared into a uranyl sensor, which gives a quite low limit of detection of 6.4 ng/L as well as excellent selectivity. Furthermore, an accurate determination is then realized in practical tap water samples. This work provides a novel strategy for designing efficient ECL sensors for trace uranyl ion monitoring in drinking water, indicating its significance in environmental and public security fields.

1,6,7-Trisubstituted perylene bisimides with tunable optical properties for colorimetric and “turn-on” fluorescence detection of HCl

To elucidate the effect of different substituents on the optical and redox properties of perylene bisimide (PBI), a novel series of 1,6,7-trisubstituted PBIs (1–6) with a highly twisted perylene core was synthesized and characterized. By substituting the hydrogen atoms at the bay-positions with various substituents (dihexylamino, piperidinyl, morpholinyl, hexoxy, and bromo), the absorption and fluorescence wavelengths of 1–6 in cyclohexane were extensively tuned within the ranges of 551–646 and 586–720 nm, respectively, simply by harnessing the electron-donating strength of the substituents. Varying the substituents generated a new family of long-wavelength absorbing and fluorescent dyes. Moreover, PBI 2 exhibited colorimetric and “turn-on” fluorescence responses in extremely acidic medium (pH 1.0 to −0.6). Low-cost test strips containing 2 were easily prepared and could be used to detect HCl.

Variable electronic structure and spin distribution in bis(2,2'-bipyridine)-metal complexes (M = Ru or Os) of 4,5-dioxido- and 4,5-diimido-pyrene.

The odd-electron compounds [M(bpy)2(L1)](ClO4) M = Ru ([1](ClO4)) or Os ([2](ClO4)), and the even-electron species [M(bpy)2(H2L2)](ClO4)2, M = Ru ([3](ClO4)2) or Os ([4](ClO4)2) were obtained from pyrene-4,5-dione, L1, or 4,5-diaminopyrene, H4L2, and were characterised structurally, electrochemically and spectroscopically. Experimental and computational analysis (TD-DFT) revealed rather different electronic structures and spin distributions of the paramagnetic monocations 1+-4+. EPR investigations and electronic absorption studies exhibit increasing metal contributions to the singly occupied MO along the series 1+ < 3+ < 4+ < 2+, illustrated by g value and long-wavelength absorbance. In addition to variations of the metal (Ru,Os) and the donor atoms (O,NH) the extension of the π system of the semiquinone-type ligand has a large effect on the electronic structure of the paramagnetic cations.

Computational Assessment of the Three-Dimensional Configuration of Dissolved Organic Matter Chromophores and Influence on Absorption Spectra.

The three-dimensional configuration of dissolved organic matter (DOM) is an important factor in determining the role of DOM in natural and engineered systems, yet there is still considerable uncertainty regarding the formation and potential stability of molecular aggregates within DOM. In this paper, we describe a computational assessment of the three-dimensional configuration of DOM. Specifically, we were interested in evaluating the hypothesis that DOM forms thermodynamically stable molecular aggregates that as a result were potentially shielded from water solvent molecules. Molecular dynamics simulations of DOM model compounds carefully selected based on ultrahigh-resolution mass spectrometry data revealed that, while DOM does indeed form molecular aggregates, the large majority of molecules (especially, O-atom bearing molecules) are solvent accessible. Additionally, these computations revealed that molecular aggregates are weak and dissociate when placed in organic solvents (tetrahydrofuran, methyl tert-butyl ether). Time-dependent density functional theory calculations demonstrated long-wavelength absorbance for both model DOM chromophores and their molecular aggregates. This study has important implications for determining the origin of DOM optical properties and for enhancing our collective understanding of DOM three-dimensional structures.

The structural basis of far-red light absorbance by allophycocyanins.

Phycobilisomes (PBS), the major light-harvesting antenna in cyanobacteria, are supramolecular complexes of colorless linkers and heterodimeric, pigment-binding phycobiliproteins. Phycocyanin and phycoerythrin commonly comprise peripheral rods, and a multi-cylindrical core is principally assembled from allophycocyanin (AP). Each AP subunit binds one phycocyanobilin (PCB) chromophore, a linear tetrapyrrole that predominantly absorbs in the orange-red region of the visible spectrum (600-700nm). AP facilitates excitation energy transfer from PBS peripheral rods or from directly absorbed red light to accessory chlorophylls in the photosystems. Paralogous forms of AP that bind PCB and are capable of absorbing far-red light (FRL; 700-800nm) have recently been identified in organisms performing two types of photoacclimation: FRL photoacclimation (FaRLiP) and low-light photoacclimation (LoLiP). The FRL-absorbing AP (FRL-AP)from the thermophilic LoLiP strain Synechococcus sp. A1463 was chosen as a platform for site-specific mutagenesis to probe the structural differences between APs that absorb in the visible region and FRL-APsand to identify residues essential for the FRL absorbance phenotype. Conversely, red light-absorbing allophycocyanin-B (AP-B; ~ 670nm) from the same organism was used as a platform for creating a FRL-AP. We demonstrate that the protein environment immediately surrounding pyrrole ring A of PCB on the alpha subunit is mostly responsible for the FRL absorbance of FRL-APs. We also show that interactions between PCBs bound to alpha and beta subunits of adjacent protomers in trimeric AP complexes are responsible for a large bathochromic shift of about ~ 20nm and notable sharpening of the long-wavelength absorbance band.

Rationally Designed Long-Wavelength Absorbing Ru(II) Polypyridyl Complexes as Photosensitizers for Photodynamic Therapy.

The utilization of photodynamic therapy (PDT) for the treatment of various types of cancer has gained increasing attention over the last decades. Despite the clinical success of approved photosensitizers (PSs), their application is sometimes limited due to poor water solubility, aggregation, photodegradation, and slow clearance from the body. To overcome these drawbacks, research efforts are devoted toward the development of metal complexes and especially Ru(II) polypyridine complexes based on their attractive photophysical and biological properties. Despite the recent research developments, the vast majority of complexes utilize blue or UV-A light to obtain a PDT effect, limiting the penetration depth inside tissues and, therefore, the possibility to treat deep-seated or large tumors. To circumvent these drawbacks, we present the first example of a DFT guided search for efficient PDT PSs with a substantial spectral red shift toward the biological spectral window. Thanks to this design, we have unveiled a Ru(II) polypyridine complex that causes phototoxicity in the very low micromolar to nanomolar range at clinically relevant 595 nm, in monolayer cells as well as in 3D multicellular tumor spheroids.

Demonstration of a Dual-Band InAs/GaSb Type-II Superlattice Infrared Detector Based on a Single Heterojunction Diode

We propose and demonstrate a new single heterojunction structure for dual-band detection based on type-II InAs/GaSb superlattices grown by metal-organic chemical vapor deposition. The structure simply consists of a p-type mid-wavelength contact layer, an n-type mid-wavelength absorber and an n-type long-wavelength absorber. At a small reverse bias, the presence of a potential barrier in the valence band between the two adjacent absorbers allows the mid-wavelength channel to work only; at a higher bias where the potential barrier no longer exists, photo-generated holes in the long-wavelength absorber are able to transport through the mid-wavelength absorber and reach the p-contact, making both channels to work. At −0.1 V and 77 K, the mid-wavelength channel exhibited a 50% cut-off wavelength of 3.5 $\mu \text{m}$ , a dark current density of $2.4\times 10^{{-9}}$ A/cm2, and a peak specific detectivity of $1.4\times 10^{{13}}$ cm $\cdot $ Hz1/2/W; while at −0.3 V the long-wavelength channel exhibited a 50% cut-off wavelength of 8.0 $\mu \text{m}$ , a dark current density of $5.1\times 10^{-7}$ A/cm2, and a peak specific detectivity of $3.6\times 10^{12}$ cm $\cdot $ Hz1/2/W.

Optimization of Long-Wavelength InAs/GaSb Superlattice Photodiodes With Al-Free Barriers

We demonstrate long-wavelength InAs/GaSb superlattice photodiodes grown on InAs substrates in a production-scale metal-organic chemical vapor deposition system. An aluminum-free heterojunction scheme was adopted where mid-wavelength superlattices served as electron barriers alongside an ${n}$ -type long-wavelength absorber. Both electrical modeling and experimental characteristics suggest that suppressed dark current and unimpeded transport of photo-generated carriers can be both achieved with engineered barrier layers. Under 77 K and a reverse bias of −0.1 V, the optimized device has shown a cut-off wavelength around 12 $\mu \text{m}$ , a blackbody responsivity of 1.01 A/W, a dark-current density of 5 $\times \,\,10^{-4}$ A/cm2 and a dark-current limited specific detectivity over 1 $\times \,\,10^{11}$ cm $\cdot \sqrt {\textrm {Hz}}$ /W.

Bidirectional Solvatofluorochromism of a Pyrrolo[3,2-b]pyrrole–Diketopyrrolopyrrole Hybrid

Hybridization of electron donors and acceptors provides routes to long-wavelength absorbing and fluorescing dyes. Varying the coupling of low-lying charge-transfer (CT) states with the ground and different locally excited states profoundly affects the photophysics of such donor–acceptor conjugates. Herein, we hybridize an electron-deficient diketopyrrolopyrrole (DPP) moiety with an electron-rich pyrrolopyrrole (PP) that is symmetrically N-arylated with 4-nitrophenyl substituents. The lowest Franck–Condon state is located on the DPP ring structure and dominates the photophysics of the hybrid. Similar to the DPP moiety, the hybrid exhibits optical absorption that is invariant to the solvent media. The PP donor considerably modulates its fluorescence by undergoing electron transfer to the locally excited DPP to form a CT state. For nonpolar media, an increase in solvent polarity causes a bathochromic shift of the fluorescence reaching the longest wavelengths for chloroform and DCM. A further increase in the ...

Semiconducting polymer dots with bright narrow-band emission at 800 nm for biological applications.

The development of near-infrared (NIR) fluorescent probes is critical for in vivo exploration of the fundamental and complex processes in living systems by noninvasive fluorescence imaging techniques. Semiconducting polymer dots (Pdots) are emerging as important probes that exhibit several advantages, such as high brightness and biocompatibility. However, NIR-emitting Pdots are very rare, particularly at the center (∼800 nm) of the first optical window of biological tissues (between 650 nm and 950 nm). In this paper, we describe the synthesis of a semiconducting polymer with bright and narrow-band emission at 800 nm. The polymer was designed by incorporating a NIR porphyrin unit into a conjugated backbone; the polymer used a cascade energy transfer to produce the signal. The resulting Pdots possessed a narrow emission bandwidth (FWHM ∼ 23 nm) and good fluorescence quantum yield (QY = 8%), which is high for a near-IR emitter. The Pdots were bioconjugated with streptavidin for specific labeling of cellular targets, yielding higher staining index when compared with commercial NIR probes, such as PE-Cy7. Moreover, the NIR polymer was combined with a long-wavelength absorbing polymer to make bright Pdots (QY = 15%) for in vivo noninvasive imaging. These NIR Pdots with surface PEGylation led to high-contrast imaging of lymph nodes and tumors in a mouse model. This work highlights the great potential of the NIR Pdots for cellular and in vivo imaging applications.

Studies of carbon monoxide dehydrogenase from Oligotropha carboxidovorans

We have undertaken physicochemical studies of the CO dehydrogenase from the aerobe Oligotropha carboxidovorans, probing both the binuclear Mo- and Cu-containing active site where CO is oxidized to CO2 and the enzyme’s FAD, where the reducing equivalents obtained from CO are transferred to the quinone pool. Regarding the FAD site, we have characterized the semiquinone oxidation state by EPR and identified it to be of the blue neutral form with a linewidth of 20G. The signature long-wavelength absorbance of FADH is also observed in the absorption spectrum of partially reduced enzyme at low pH. The enzyme exhibits a pH-dependent absorption spectrum in the oxidized state that is lost upon covalent modification of the enzyme by the flavin-specific agent diphenyliodonium cation. The pH dependence is attributed to Tyr 193 of the FAD-containing CoxM subunit, which sits atop the re face of the isoalloxazine ring in van der Waals contact with it. Electron equilibration among the enzyme’s four redox-active centers (including two [2Fe-2S] clusters in addition to the binuclear center and FAD) is found to be pH-dependent, but too fast to be followed using a stopped-flow pH jump protocol. Electron transfer from the iron-sulfur clusters to the FAD is thus much faster than in other members of the xanthine oxidase family of molybdenum-containing enzymes to which CO dehydrogenase belongs. Finally, a complex of the binuclear center with bicarbonate has been characterized by EPR, where the absence of observed hyperfine coupling using 13C-labeled bicarbonate suggests strongly that the bicarbonate is not directly coordinated to the Mo(V) of the partially reduced binuclear center.

DNA-Based Assemblies for Photochemical Upconversion.

In the present study DNA was used as a scaffold for the supramolecular assembly of organic chromophores for photochemical upconversion (PUC). Initially, a green-to-blue PUC was observed using free chromophores in solution: tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)3](2+), which acts as a long-wavelength absorber (λex = 500 nm), and an in situ energy donor to an acceptor (R)-1-O-[4-(1-pyrenylethynyl)phenylmethyl]glycerol (PEPy or TINA monomer), which acts as an annihilator and short-wavelength photoemitter (λem = 420 nm). Then, DNA duplexes possessing TINA monomers were synthesized, and complexes with [Ru(bpy)3](2+) were investigated. In contrast to the dynamic interactions of [Ru(bpy)3](2+) with TINA monomer free in solution, ground-state complex formation was the predominant mechanism of interaction between [Ru(bpy)3](2+) and DNA duplexes bearing two TINA monomers at the 5' ends as shown by fluorescence, circular dichroism (CD), and UV-vis spectroscopy studies. The use of TINA-modified DNAs led to PUC occurring at concentrations significantly lower than that for free chromophores in solution: 2.5 μM [Ru(bpy)3](2+) and 5.0 μM TINA-modified duplex in the DNA-based systems in aqueous buffer versus 46 μM [Ru(bpy)3](2+) and 4.6 mM TINA monomer for the free donor and acceptor in DCM, respectively. Providing vast capabilities of DNA in the development of novel photonic systems as a result of the controllable organization of various chromophores, this study opens a new perspective for the development of DNA-based light-harvesting systems using PUC.

Improvement of Light Harvesting by Addition of a Long-Wavelength Absorber in Dye-Sensitized Solar Cells Based on ZnO and Indoline Dyes

A pathway to improve the light-harvesting efficiency of dye-sensitized solar cells based on porous electrodeposited ZnO films is presented. Cosensitization with the indoline dyes D149 and D131 and the squaraine dye SQ2 leads to panchromatic light harvesting and photovoltaic activity. When coadsorbates are employed to prevent dye aggregation on the ZnO surface, an increase in the short-circuit photocurrent and overall efficiency compared to reference cells with D149, or D149 and D131 is attained. The overall performance of cosensitized cells containing SQ2, however, is limited by low open-circuit voltages and fill factors. By use of electrochemical impedance spectroscopy, current–voltage characterization in the dark and under illumination, and charge extraction measurements, recombination reactions and the distribution of trap states in the ZnO films are investigated, and the origins of the limited open-circuit voltages and fill factors in cells with SQ2 are revealed.

Rational design of long-wavelength absorbing and emitting carbostyrils aided by time-dependent density functional calculations

We have used computational chemistry methods to aid the rational design of long-wavelength absorbing and emitting organic materials. For this purpose, the vertical electronic transition energies of 3,4-dicyano carbostyrils (quinolone-2(1H)-ones) substituted by electron-donating substituents (methoxy, methylamino, dimethylamino) at positions 6 and 7, are calculated by time-dependent density functional theory (B3LYP) within the Tamm–Dancoff approximation. Bulk solvent effects (DMSO, CH3CN, H2O) were taken into account by the CPCM solvation model. Particular long-wavelength absorptions (∼540nm) are predicted for derivatives containing an amino group in position 6 irrespective of whether a 7-methoxy or a 7-amino group is present. In contrast, considerably shorter wavelength absorption (∼440nm) can be expected for 6-methoxy-7-amino substituted 3,4-dicyano carbostyrils. Optimization of the first excited singlet state of 6-dimethylamino substituted carbostyrils leads to a perpendicular arrangement of the (CH3)2N-group with respect to the heterocyclic ring system accompanied by an extremely low electronic transition energy (1000–1500nm) with vanishingly small intensity (oscillator strength f<0.000). 6-methoxy-7-amino substituted carbostyrils are predicted to emit at 490–520nm. An especially long-wavelength fluorescence (∼660nm) is calculated for 6-amino-7-methoxy- as well as 6,7-bis(methylamino)-3,4-dicyanocarbostyril.

Site-specific insertion of selenium into the redox-active disulfide of the flavoprotein augmenter of liver regeneration

Augmenter of liver regeneration (sfALR) is a small disulfide-bridged homodimeric flavoprotein with sulfhydryl oxidase activity. Here, we investigate the catalytic and spectroscopic consequences of selectively replacing C145 by a selenocysteine to complement earlier studies in which random substitution of ∼90% of the 6 cysteine residues per sfALR monomer was achieved growing Escherichia coli on selenite. A selenocysteine insertion sequence (SECIS) element was installed within the gene for human sfALR. SecALR2 showed a spectrum comparable to that of wild-type sfALR. The catalytic efficiency of SecALR2 towards dithiothreitol was 6.8-fold lower than a corresponding construct in which position 145 was returned to a cysteine residue while retaining the additional mutations introduced with the SECIS element. This all-cysteine control enzyme formed a mixed disulfide between C142 and β-mercaptoethanol releasing C145 to form a thiolate-flavin charge transfer absorbance band at ∼530nm. In contrast, SecALR2 showed a prominent long-wavelength absorbance at 585nm consistent with the expectation that a selenolate would be a better charge-transfer donor to the isoalloxazine ring. These data show the robustness of the ALR protein fold towards the multiple mutations required to insert the SECIS element and provide the first example of a selenolate to flavin charge-transfer complex.

Long-Wavelength Absorbing and Fluorescent Chameleon Labels for Proteins, Peptides, and Amines

Long-wavelength absorbing labels that change their color and fluorescence upon conjugation to proteins and other biomolecules provide two critical advantages over the wealth of conventional amine-reactive labels. At first, the progress of the labeling reaction can be monitored continuously either visually or by spectrometry without prior purification. Then, the labeled biomolecule can be investigated with red or near-infrared light, which minimizes background interference in biological samples. These unique characteristics are met by a group of long-wavelength absorbing cyanine dyes carrying a reactive chloro substituent for nucleophilic substitution with primary amines, which is accompanied by a color change from green to blue. In addition to this so-called chameleon effect, the dyes display an increase in fluorescence during the labeling reaction. Despite their structural similarity, the reactivity of the dyes differs strongly. The fastest labeling kinetics is observed with dye S 0378 as its five-membered ring affords a stabilizing effect on the intermediate carbocation during an S(N)1-type of nucleophilic substitution. The reaction mechanism of the amine-reactive cyanine dyes provides a blueprint for the design of future long-wavelength absorbing chameleon dyes.

Benzodipyrrolenine-based biscyanine dyes: Synthesis, molecular structure and spectroscopic characterization

A novel method of synthesizing long-wavelength absorbing and emitting bis-trimethine dyes that consists of condensing benzodipyrrolenine dialdehyde with quaternized heterocyclic CH-acidic compounds was used to prepare a series of biscyanines. The new method is more convenient than its conventional counterepart, which relies upon condensation of a quaternized benzodipyrrolenine with Fisher's aldehyde, for the synthesis of a symmetrically substituted dyes that contain various heterocyclic end-groups. Investigations of the spectral and luminescent properties of the dyes in solution revealed that the absorption (596–717 nm) and emission (629–773 nm) maxima of the biscyanines were red-shifted by ∼100 nm compared to the parent “monomeric” cyanine that contained only one chromophoric polymethine system. The prepared dyes have high extinction coefficients (≤251,000 M −1 cm −1) and quantum yield (≤28%). Substitution of both terminal benzoxazole moieties with indolenine, benzothiazole, 2- and 4-quinoline imparted a red-shift in the absorption and emission maxima but lowered quantum yield.

Spectroscopic and Kinetic Studies of Y114F and W116F Mutants of Me2SO Reductase from Rhodobacter capsulatus

Mutants of the active site residues Trp-116 and Tyr-114 of the molybdenum-containing Me(2)SO reductase from Rhodobacter capsulatus have been examined spectroscopically and kinetically. The Y114F mutant has an increased rate constant for oxygen atom transfer from Me(2)SO to reduced enzyme, the result of lower stability of the E(red).Me(2)SO complex. The absorption spectrum of this species (but not that of either oxidized or reduced enzyme) is significantly perturbed in the mutant relative to wild-type enzyme, consistent with Tyr-114 interacting with bound Me(2)SO. The as-isolated W116F mutant is only five-coordinate, with one of the two equivalents of the pyranopterin cofactor found in the enzyme dissociated from the molybdenum and replaced by a second Mo=O group. Reduction of the mutant with sodium dithionite and reoxidation with Me(2)SO, however, regenerates the long-wavelength absorbance of functional enzyme, although the wavelength maximum is shifted to 670 nm from the 720 nm of wild-type enzyme. This "redox-cycled" mutant exhibits a Me(2)SO reducing activity and overall reaction mechanism similar to that of wild-type enzyme but rapidly reverts to the inactive five-coordinate form in the course of turnover.

Long-wavelength semiconductor saturable absorber mirrors using metamorphic InP grown on GaAs by molecular beam epitaxy

Metamorphic growth of InP on GaAs has been used to tailor the recovery time of 1.55μm semiconductor saturable absorber mirrors. By decreasing the thickness of the InP “lattice reformation layer” grown between a GaAs-based distributed Bragg reflector and the active region, we were able to purposely reduce the recovery time. For thickness of the reformation layer below 200nm, the semiconductor saturable absorber mirrors exhibited a short absorption recovery time enabling a robust, self-starting passive mode-locked operation of an erbium-doped fiber laser. We are also reporting preliminary results on the stability of the saturable absorbing mirrors parameters after rapid thermal annealing.