Sensitizer Molecules Research Articles

Examining the role of acceptor molecule structure in self-assembled bilayers: surface loading, stability, energy transfer, and upconverted emission.

Self-assembly of sensitizer and acceptor molecules has recently emerged as a promising strategy to facilitate and harness photon upconversion via triplet-triplet annihilation (TTA-UC). In addition to the energetic requirements, the structure and relative orientation of these molecules can have a strong influence on TTA-UC rates and efficiency. Here we report the synthesis of five different acceptor molecules composed of an anthracene core functionalized with 9,10- or 2,6-phenyl, methyl, or directly bound phosphonic acid groups and their incorporation into self-assembled bilayers on a ZrO2 surface. All five films facilitate green-to-blue photon upconversion with Φuc as high as 0.0023. The efficiency of TTA, and not triplet energy transfer, fluorescence, or losses via FRET, was primarily responsible for dictating the Φuc emission. Even for molecules having similar photophysical properties, variation in the position of the phosphonic acid resulted in dramatically different ΦTTA, Ith values, γTTA, and D. Interestingly, we observed a strong linear correlation between ΦTTA and the Ith value but the cause of this relationship, if any, is unclear.

Influence of meta- and para-phosphonated diphenylanthracene on photon upconversion in self-assembled bilayers

It is well known that the rate and efficiency of photon upconversion via triplet–triplet annihilation (TTA-UC) are strongly dependent on the energetics of the sensitizer and acceptor molecules. In rigid scaffoldings, where the dyes are fixed in position, the structure and orientation of the molecules also presumably play an important role. We investigate how the variation in the position of the phosphonate surface binding group on 9,10-diphenylanthracene influences TTA-UC in self-assembled bilayers on ZrO2. Interestingly, meta- or para-substitution of the anthracene dye with phosphonate groups had minimal influence on their energetics, surface loadings, or sensitizer to acceptor triplet energy transfer efficiency. However, the TTA-UC efficiency is three times lower with the meta-substituted dye, which is attributed to its threefold decrease in its triplet excited state lifetime relative to the para-substituted dye.

Kinetically controlled crystal growth approach to enhance triplet energy migration-based photon upconversion

Improving efficiency of triplet–triplet annihilation-based photon upconversion (TTA-UC) in crystalline media is challenging because it usually suffers from the severe aggregation of the donor (sensitizer) molecules in acceptor (emitter) crystals. We show a kinetically controlled crystal growth approach to improve donor dispersibility in acceptor crystals. As the donor–acceptor combination, a benchmark pair of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA) is employed. A surfactant-assisted reprecipitation technique is employed, where the concentration of the injected PtOEP–DPA solution holds the key to control dispersibility; at a higher PtOEP–DPA concentration, a rapid crystal growth results in better dispersibility of PtOEP molecules in DPA crystals. The improvement of donor dispersibility significantly enhances the TTA-UC quantum yield. Thus, the inherent function of donor-doped acceptor crystals can be maximized by controlling the crystallization kinetics.

Spectral Photosensitization of Optical Anisotropy in Solid Poly(Vinyl Cinnamate) Films

The possibility and features of formation of sensitized photoinduced optical anisotropy in amorphous films of poly(vinyl cinnamate) and its derivative poly(vinyl-4-metoxicinnamate) under the action of polarized light (including light that is not absorbed by polymer macromolecules themselves) have been investigated. It is found that the effect of induced optical anisotropy is based on the transfer of electron excitation energy from donor (sensitizer) molecules to acceptor molecules and is observed in the course of phototopochemical biomolecular cyclization reaction of cinnamate fragments in polymer macromolecules. The detected photoinduced anisotropy in solid films of poly(vinyl cinnamate) and its derivative poly(vinyl-4-metoxicinnamate) ensures sensitized photo-orientation of low-molecular thermotropic liquid crystals.

Sonophotodynamic therapy mediated by liposomal zinc phthalocyanine in a colon carcinoma tumor model: Role of irradiating arrangement.

Objective(s):Low penetration depth of light is the main defect of photodynamic therapy (PDT), which could be improved by sonodynamic therapy (SDT). In this study, a combination of PDT and SDT known as sonophotodynamic therapy (SPDT) was investigated using two reverse arrangements in CT26 tumor model.Materials and Methods:The liposomal zinc phthalocyanine was synthesized and characterized. It was then administered to CT26 tumor models as a sensitizer. The animal models were subjected to PDT, SDT, and the combined treatment in different groups. The doubling time for the survival of tumors and animals was considered as a measure to evaluate treatments efficacy.Results:In all treatment groups there was a significant decline in tumor volume 15 days after treatment compared to the main control group, but the optimum response was observed in the group receiving a combined treatment with the priority of PDT. 120 days after treatment, in the groups treated by PDT and SDT, the tumor shrank by 20%, while in the group receiving SPDT with PDT priority, 80% of tumors was recovered. No case of complete tumor progression was observed in SPDT group with SDT priority. This could be due to the pores created in cell membranes during ultrasound irradiation of the tumor, which removed the sensitizer molecules from the cells and reduced PDT efficacy in SPDT group with SDT priority.Conclusion:It seems that SPDT with PDT priority offers a more efficient alternative than each of PDT, SDT individually or SPDT with the reverse arrangement.

Elucidating the Energy- and Electron-Transfer Dynamics of Photon Upconversion in Self-Assembled Bilayers

Self-assembled bilayers of acceptor (A) and sensitizer (S) molecules on a metal oxide surface is a promising strategy to facilitate photon upconversion via triplet–triplet annihilation (TTA-UC) and extract charge from the upconverted state. The hypothesized mechanism for TTA-UC in a bilayer film includes low energy light absorption, triplet energy transfer, cross-surface energy migration, triplet–triplet annihilation, and electron injection into TiO2. Nonproductive processes can also occur including sensitizer-sensitizer TTA, radiative/nonradiative decay, back-electron transfer, and others. Steady-state and time-resolved emission/absorption spectroscopy were used to determine the rate constants of these processes. The rate constants indicate that S to A triplet energy transfer as well as S and A nonradiative rates are the primary efficiency-limiting processes for TTA-UC at the interface. This information is necessary to guide the design of new self-assembled UC films and is a critical stepping stone towar...

Hydrophobic painting materials fast detection using temperature dependence SERS on simple or PEGylated Ag nanoparticles

In conservation and restauration efforts, fast, sensitive and reliable identification of authentic materials is crucial. We provide here the first report on the possibility to unambiguously detect hydrophobic painting materials within one second acquisition time using a compact, portable Raman instrument and surface enhanced Raman scattering (SERS) technique. SERS detection of organic materials used in artwork was improved by a simple control of the colloid application temperature. Pure citrate- and hydroxylamine-reduced silver nanoparticles (AgNPs), as well as their polyethylene glycol (PEG) functionalized version were tested at different substrate temperatures by using a conventional, largely used SERS sensitizer molecule, p-amionothiophenol (pATP). It was shown that SERS efficiency increased with temperature in all cases. Best results regarding stability and enhancement were obtained for PEGylated NPs. Such NPs were further used to detect a cochineal extract, one of the natural organic dyes employed in painting/textile manufacturing, as well as for oleic acid, one of the main constituents of linseed oil and major indicator of any oil-based painting technique.

Hierarchical self-supported ZnAlEu LDH nanotubes hosting luminescent CdTe quantum dots.

Self-supported oligo-layered ZnAlEu LDH nanotubes (∅ 20 nm) self-assemble upon controlled hydrolysis of the metal ions (Zn2+, Al3+, Eu3+) in the presence of 1,3,5-benzenetricarboxylate anions and non-ionic worm-like micelles. Their high surface area and easily accessible cylindrical mesopores (175 m2 g-1; 0.75 cm3 g-1) facilitate interaction with 5 nm CdTe quantum dots, enhancing the overall luminescence behavior.

Investigation on the influences of layer structure and nanoporosity of light scattering TiO2 layer in DSSC

Dye-sensitized solar cell (DSSC) is one of promising photovoltaic materials due to its simplicity in fabrication process and rich variety of possible sensitizer molecules. DSSC cell is commonly constructed of TiO2 layer as photoelectrode, dye as photosensitizer, electrolyte as redox mediator, and platinum layer as counter electrode. TiO2 layer is often constructed from different types of layers, such as blocking layer, transparent layer, microchannel or light scattering layer, which is made usually by successive layer-by-layer process. In this work, different TiO2 layers with different thickness and heat treatment were prepared and then used to build a complete sandwich-type DSSC. The characterization results show that the power conversion efficiency (PCE) is slightly reduced when using TiO2 layer with multiple scattering layers. This reduction is caused by an increase in the resistance from charge transport and charge transfer inside the mesoporous TiO2 layer, as revealed from the electrochemical impedance spectroscopy measurement results. Additional heat treatment introduced at the final step in the TiO2 layer preparation process, however, slightly improve the cell performance. Although this heat treatment does not produce significant change in porosity or pore size distribution of the TiO2 layer, it might be able to improve the contact between the TiO2 nanoparticles. The best PCE achieved in this work is about 5.3%, which was observed in the cell using TiO2 layer with one scattering layer and additional heat treatment.

Photocatalytic degradation of persistent organic pollutants under visible irradiation by TiO2catalysts sensitized with Zn(II) and Co(II) tetracarboxy-phthalocyanines

Photo-excitation under visible light has been an important step to acquire solar-driven TiO2photocatalysts and dye sensitization has been used frequently to extend the optical response of TiO2into the visible region. In the present work, new heterogeneous photocatalysts were prepared by anchoring carboxylic acid substituted Zn(II) and Co(II) phthalocyanines onto polycrystalline TiO2surface and their photocatalytic activities were investigated. Due to covalent bonding of carboxy-terminated molecules onto TiO[Formula: see text]semiconductors, we synthesized symmetric 4-hydroxybenzoic acid-bearing metallophthalocyanines as dye sensitizer molecules. Heterogeneous composites having titanium dioxide and metallophthalocyanines anchored via CO–O–TiO2bonds were characterized by using X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FT-IR), and ultraviolet-visible diffuse reflectance spectroscopy. The optimum loading value of the dyes on TiO2were 0.98 [Formula: see text]mol/g TiO2for CoPc and 0.86 [Formula: see text]mol/g TiO2for ZnPc, nearly independent of the amount of TiO2used. These newly obtained heterogeneous photocatalysts were employed in the photocatalytic degradation of 4-chlorophenol(4-CP), chlorobenzene(CB) and 1,2,4-trichlorobenzen(TCB) in aqueous media under visible irradiation. Gas chromatography-mass spectrometry (GC-MS) was used for quantitation. The new photocatalysts showed excellent activities with visible-region irradiation in the photocatalytic degradation of persistent organic pollutants (POPs) as compared to the control experiments used with untreated TiO2and the difference was attributed to the cooperation of the two elements, namely TiO2and MPc. Experiments show that in two hours nearly complete degradation of POPs were observed.

Charge Delocalization in the Cascade Band Structure CdS/CdSe and CdS/CdTe Core–Shell Sensitized with Re(I)–Polypyridyl Complex

Charge-carrier dynamics of CdS quantum dot (QD) and CdS/CdSe type-I and CdS/CdTe type-II core–shell nanocrystals (NCs) sensitized with a Re(I)–polypyridyl complex have been carried with special emphasis on studies on carrier delocalization and the role of Re-complex as a hole acceptor and sensitizer molecule. Our investigation confirmed photoexcited hole transfer from CdS and CdS/CdSe to the Re-complex, while no hole transfer was observed in the CdS/CdTe–Re-complex system. This was rationalized by the evaluation of the relative energy levels, which revealed that such hole migration was not energetically favorable due to low-lying highest occupied molecular orbital (HOMO) of the Re-complex as compared with the valence band (VB) of CdTe shell; however, luminescence quenching from upper excited states of Re-complex was observed in the presence of all three QD and core–shell systems, which has been attributed to electron injection from hot state (energetically higher than the LUMO state) of the Re-complex to ...

Integrated Photon Upconversion Solar Cell via Molecular Self-Assembled Bilayers

Molecular photon upconversion, by way of triplet–triplet annihilation (TTA-UC), is an intriguing strategy to increase solar cell efficiencies beyond the Shockley–Queisser limit. Here we introduce self-assembled bilayers of acceptor and sensitizer molecules on high surface area electrodes as a means of generating an integrated TTA-UC dye-sensitized solar cell. Intensity dependence and IPCE measurements indicate that bilayer films effectively generate photocurrent by two different mechanisms: (1) direct excitation and electron injection from the acceptor molecule and (2) low-energy light absorption by the sensitizer molecule followed by TTA-UC and electron injection from the upconverted state. The power conversion efficiency from the upconverted photons is the highest yet reported for an integrated TTA-UC solar cell. Energy transfer and photocurrent generation efficiency of the bilayer device is also directly compared to the previously reported heterogeneous UC scheme.

NIR-Sensitized Photoinitiated Radical Polymerization and Proton Generation with Cyanines and LED Arrays

Abstract Photoinitiated radical polymerization using as photoinitiator system a combination of NIR-sensitizer (Sens) and a radical initiator (RI) was investigated in different multifunctional monomers derived from the multifunctional acrylic esters HDDA, TPGDA, PEGDA, and TMPTA. NIR-LEDs were applied for exposure exhibiting their emission maximum either at 750 nm, 790 nm, 830 nm or 940 nm. Solubility of Sens in the respective monomers, their absorption data (λabsmax, emax), fluorescence data (Φf, λfmax), electrochemical data (Eox, Ered) and the free energy of electron transfer (ΔGel) between the excited state of Sens and RI were compiled. It showed for many systems an exothermic behavior, which does not always correlate with reactivity. Iodonium salts with low coordinating anions ([B(Ph)4]−, [B(Ph-F5)4]−, [(CF3SO2)2N]-, PF6−) and Triazine A (2,4-Bis(trichloromethyl)-6-(4-methoxy)phenyl-1,3,5-triazine) were applied as RI. Sens was selected from the group of cyanines in which neutral compounds exhibited the highest reactivity. Cationic sensitizers showed almost no initiating reactivity. Furthermore, the sensitizer (5-(6-(2-(3-Ethyl-1,1-dimethyl-1H-benzo[e]indol-2(3H)-ylidene)ethylidene)-2-(2-(3-ethyl-1,1-dimethyl-1H-benzo[e]indol-3-ium-2-yl)vinyl)cyclohex-1-en-1-yl)-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate) (S9) was taken to study the effect of wavelength dependent LED excitation. The highest reactivity was found for the LED emitting at 850 nm where the system possesses the highest excitation volume and the lowest absorption of photoproducts. Furthermore, thermal investigation approved that the combination S9 and iodonium salt can be considered as a thermal initiation system either. Thus, these systems can be seen as hybrid initiator systems. Finally, we show for the first time the generation of solvated protons using different iodonium salts and sensitizers in acetone as surrounding. The activity of solvated protons was evaluated showing a certain reactivity tendency. The number of solvated protons with respected to the number of sensitizer molecules was lower than unity showing their consumption by nucleophilic centers.

Improving Light Harvesting in Dye-Sensitized Solar Cells Using Hybrid Bimetallic Nanostructures

In this work we demonstrate improved light trapping in dye-sensitized solar cells (DSSCs) with hybrid bimetallic gold core/silver shell nanostructures. Silica-coated bimetallic nanostructures (Au/Ag/SiO2 NSs) integrated in the active layer of DSSCs resulted in 7.51% power conversion efficiency relative to 5.97% for reference DSSCs, giving rise to 26% enhancement in device performance. DSSC efficiencies were governed by the particle density of Au/Ag/SiO2 NSs with best performing devices utilizing only 0.44 wt % of nanostructures. We performed transient absorption spectroscopy of DSSCs with variable concentrations of Au/Ag/SiO2 NSs and observed an increase in amplitude and decrease in lifetime with increasing particle density relative to reference. We attributed this trend to plasmon resonant energy transfer and population of the singlet excited states of the sensitizer molecules at the optimum concentration of NSs promoting enhanced exciton generation and rapid charge transfer into TiO2.

Dynamics of Electron Recombination and Transport in Water-Splitting Dye-Sensitized Photoanodes

Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) use visible light to split water using molecular sensitizers and water oxidation catalysts codeposited onto mesoporous TiO2 electrodes. Despite a high quantum yield of charge injection and low requirement for the catalytic turnover rate, the quantum yield of water splitting in WS-DSPECs is typically low (<1%). Here we examine the charge separation and recombination processes in WS-DSPECs photoanodes functionalized with varying amounts of IrO2 nanoparticle catalyst. Charge extraction and transient open-circuit voltage decay measurements provide insight into the relationship between light intensity, conduction band electron density, open-circuit photovoltage, and recombination time scale. We correlate these results with electrochemical impedance spectroscopy and present the first complete equivalent circuit model for a WS-DSPEC. The data show quantitatively that recombination of photoinjected electrons with oxidized sensitizer molecules a...

Metal-free synthesis of bisthiophene-core donor acceptor organic photosensitizers for dye-sensitized solar cells

Three novel donor-π-acceptor molecules with a bis-thiophene core have been synthesized through a simple and versatile metal-free synthetic procedure. Study of their optical and electrochemical properties, and a preliminary evaluation of their use as dyes in dye sensitized solar cells (DSSC) are presented. The proposed synthetic protocol results in a drastic reduction of the size and complexity of the sensitizer molecule, possibly enabling cost decrease by overall yield improvement and easy scalability. Particular attention has been paid to limit the environmental impact by reducing the number of synthetic steps and especially avoiding the use of organometallic reactions.

Highly crystalline Titania nanotube arrays realized by hydrothermal vapor route and used as front-illuminated photoanode in dye sensitized solar cells

Highly crystalline TiO2 nanotube arrays (TNTAs) film is easily realized by treating its amorphous film under the hydrothermal vapor (HV) environment. The freestanding TNTAs film can be lift-off from the Ti foil, which serves as photoanode based on FTO substrate after the transplanting procedure. Compared to the thermal annealing (TA) treated TNTAs photoanode, the HV treated photoanode possesses some excellent properties, such as long optical path, fast charge transporting and easy adsorption of the sensitizer molecules, which can result in high short current density. Notably, the N719 dye sensitized HV treated photoanode prepared under 180 °C shows relatively high photovoltaic response in the visible range due to its hierarchical structure, which gives an impressive performance conversion efficiency of 8.11% without any surface modification. And the present work sheds light on the application of the mild crystalline strategy for performance improvement of the DSSCs based on TiO2 nanotube arrays photoanode.

Ultrafast Electron Injection, Hole Transfer, and Charge Recombination Dynamics in CdSe QD Super-Sensitized Re(I)–Polypyridyl Complexes with Catechol and Resorcinol Moiety: Effect of Coupling

Ultrafast charge-transfer dynamics have been demonstrated in CdSe quantum dots (QD) using two Re(I)–polypyridyl complexes having pendent catechol (Re1,2) and resorcinol (Re1,3) as the sensitizer molecules. The energy level diagram of CdSe QD and Re1,2 and Re1,3 sensitizer reveals that photoexcited hole of CdSe QD can be transferred to both Re1,2 and Re1,3 molecule, and photoexcited Re1,2 and Re1,3 can inject electron in the conduction band, which has been confirmed by steady-state and time-resolved photoluminescence studies with selective photoexcitation. Femtosecond transient absorption studies have been carried out to monitor charge-transfer dynamics in early time scale. Transient absorption spectra show formation of cation radicals for both Re1,2 and Re1,3 in the 550–650 nm region with a peak at 590 nm region and broad absorption in the 650–1000 nm region, which can be attributed to photoexcited electron in the conduction band of CdSe QD. Charge recombination was determined by monitoring the decay of cation radicals as well as decay of an electron and found to be slower in the Re1,3/CdSe system as compared to that of the Re1,2/CdSe system, which is due to weaker electronic coupling in the former system.

Reversible oxygen addition on a triplet sensitizer molecule: protection from excited state depopulation.

We demonstrate that photoactivated oxygen addition to diphenylanthracene moities can be used as a tool for protection of porphyrin's phosphorescence against oxygen quenching. Phosphorescent palladium(II) tetrabenzoporphyrin, covalently linked to four diphenylanthracene moieties, was synthesized and studied. Upon irradiation with ambient light or red laser in solution in air, addition of oxygen and formation of the corresponding endoperoxides were observed. Heating of the irradiated samples afforded the parent porphyrin material.

Sensitization of the photoelectric effect in carbazole- and indolocarbazole-containing poly(phenylquinoline)s by benzothiadiazole acceptor molecules

The efficient sensitization of the photoelectric effect in mixed compositions of poly(phenylquinoline)s (PPQ) with 2,1,3-benzothiadiazole (BTDZ) molecules is established. The introduction of 10 wt % BTDZ results in extension of the spectral sensitivity range of PPQ and an increase in the photosensitivity and photocurrent by factors of 4.5 and more than 6, respectively. It is shown that the effect is caused by complex formation between PPQ donor fragments and BTDZ acceptor molecules; the strongest, in comparison with the increase in photosensitivity, is probably caused by the transport of free photogenerated carriers (electrons) over sensitizer molecules introduced into the polymer.