Near-infrared unsymmetrical squaraine core-based sensitizers for co-sensitized high-photocurrent dye-sensitized solar cells

Increased conversion of near-infrared (NIR) photons to electricity is needed to improve dye-sensitized solar cells (DSCs). Here, we report two squaraine dyes (RR13 and RR14) with unsymmetrical cores as NIR dyes in DSCs. Both dyes feature a conjugated indolizine donor with an indoline donor on the opposite side of the squaraine core. The dyes are studied via absorption spectroscopy, computational interrogation, and electrochemical analysis. The use of the strongly donating indolizine donor results in NIR photon-to-current conversion extending beyond 800 nm on TiO2 in DSC devices. The DSC devices were characterized by current-voltage curves, incident photon-to-current conversion efficiency measurements, and electrical impedance spectroscopy. After co-sensitized DSC device optimizations, the NIR-absorbing squaraine dyes complemented with commercial organic dyes (D35 and Y123) gave a high photocurrent output of ∼21 mA/cm2 with a PCE of 9.4%

Pyridyl CO\u3csub\u3e2\u3c/sub\u3eFixation Enabled by a Secondary Hydrogen Bonding Coordination Sphere

Copyright © 2020 American Chemical Society. Reversible CO2 binders under ambient conditions are of significant interest for multiple applications in sensing and capture technologies. In this paper, a general systematic way to evaluate CO2 receptors with π-systems is put forward. A series of receptors (five pyridine-based and one triazine-based) are evaluated as CO2 binders in terms of number of hydrogen bonding sites, strength of hydrogen bond donors, and number of nucleophilic sites. The binding of CO2 to the receptors was probed by computational models, absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and 1H NMR studies. Multiple solvents with varying ionic strength additives are probed to analyze the effects on CO2-bound intermediates. The receptors were screened progressively down-selecting through the different analytical techniques arriving at a promising pyridine receptor, which shows evidence of CO2 binding with each of the analytical techniques. The diaminopyridine motif demonstrates reversible CO2 binding and has convenient substitution sites for derivatization to incorporate into functional sensor systems

SWIR Emissive RosIndolizine Dyes With Nanoencapsulation In Water Soluble Dendrimers

Shortwave infrared (SWIR) emission has great potential for deep-tissue in vivo biological imaging with high resolution. In this article, the synthesis and characterization of two new xanthene-based RosIndolizine dyes coded PhRosIndz and tolRosIndz is presented. The dyes are characterized via femtosecond transient absorption spectroscopy as well as steady-state absorption and emission spectroscopies. The emission of these dyes is shown in the SWIR region with peak emission at 1097 nm. TolRosIndz was encapsulated with an amphiphilic linear dendritic block co-polymer (LDBC) coded 10-PhPCL-G3 with high uptake yield. Further, cellular toxicity was examined in vitro using HEK (human embryonic kidney) cells where a \u3e90% cell viability was observed at practical concentrations of the encapsulated dye which indicates low toxicity and reasonable biocompatibility

Oxidative Heck Reactions with Terminal Olefins

Sequential transformations in a single reaction have the potential to dramatically increase efficiency with respect to resources, time, and number of steps to access key intermediates. When sequential C-H bonds are activated a bifunctional handle arises from seemingly inert functionality. This work describes a one-pot sequential allylic C-H esterification, vinylic C-H arylation. A previously reported Pd(II)/sulfoxide system is used to generate branched allylic esters from ??-olefins with only the addition of an aryl boronic acid to the reaction mixture. Styrenyl allylic esters are generated in good overall yield and excellent selectivities. The wide functional group tolerance and mild conditions of this three-component coupling reaction provide an attractive manifold for the rapid build-up of dense functionality around terminal olefins with minimal protecting group strategies or undesirable oxidation/reduction reactions.The synthetic utility of this reaction has been demonstrated through the synthesis of several intermediates to biologically active molecules. The ready availability and inertness of ??-olefins relative to the oxidized precursors required for other C???C bond forming methods means that fewer steps are required for their installation and maintenance throughout a synthetic sequence. Previously, allylic esters served as non-resonance directing groups on terminal olefin for the vinylic C???H arylation (Heck reaction). This manifold is unique because previous intermolecular Heck reaction conditions require an excess of resonance activated olefin coupling partner. Further exploration of directing groups to determine the underlying directing factors led to the discovery of several terminal olefin classes with diversedirecting elements. A general and highly selective intermolecular Heck arylation of non-resonance stabilized ??-olefins with aryl and stryenyl boronic reagents has been developed. The Pd(II)/sulfoxide catalyzed Heck reaction is performed under oxidative, acidic conditions and proceeds with good yields and excellent regio- and stereoselectivities to generate linear E-arylated olefins. Polyenes are prevalent motiefs in natural products and pharmaceuticals. Polyene functionality often requires mild and selective synthetic methods. The Heck vinylation uses orthogonally reactive C-H bonds and these bonds are often easy to carry through synthetic sequences. Despite this advantage, the synthetic potential of the intermolecular Heck reaction has not been realized in complex molecule formation. A method has been developed which overcomes the previous intermolecular Heck-vinylation shortcomings of excess terminal olefin and required resonance activation for regio- and stereoselectivities. The Pd(II)/sulfoxide catalyzed oxidative Heck vinylation proceeds under mild conditions to give polyene products with a variety of substitution patterns amid diverse functionality. The polyenes are formed in synthetically relevant yields with excellent stereoselectivities. Overall, the oxidative Heck vinylation compares favorably with many of the methods commonly used to synthesize polyunsaturated hydrocarbon segments. This method increases the synthetic potential of the intermolecular Heck reaction closer to that of other classic palladium cross-couplings

Harnessing Photovoltage: Effects of Film Thickness, TiO₂ Nanoparticle Size, MgO and Surface Capping with DSCs

High photovoltage dye-sensitized solar cells (DSCs) offer an exceptional opportunity to power electrocatalysts for the production of hydrogen from water and the reduction of CO₂ to usable fuels with a relatively cost-effective, low-toxicity solar cell. Competitive recombination pathways such as electron transfer from TiO₂ films to the redox shuttle or oxidized dye must be minimized to achieve the maximum possible photovoltage (<i>V</i>_oc) from DSC devices. A high <i>V</i>_oc of 882 mV was achieved with the iodide/triiodide redox shuttle and a ruthenium NCS-ligated dye, <b>HD-2-mono</b>, by utilizing a combined approach of (1) modulating the TiO₂ surface area through film thickness and nanoparticle size selection, (2) addition of a MgO insulating layer, and (3) capping available TiO₂ film surface sites post film sensitization with an F-SAM (fluorinated self-assembled monolayer) treatment. The exceptional <i>V</i>_oc of 882 mV observed is the highest achieved for the popular NCS containing ruthenium sensitizers with >5% PCE and compares favorably to the 769 mV value observed under common device preparation conditions

N-heterocyclic carbene gold complexes in a photocatalytic CO2 reduction reaction

Molecular catalysts that are durable and highly selective in the photocatalytic CO2 reduction reaction (PCO2RR) are in high demand. Molecular gold complexes are underexplored in the CO2RR manifold despite heterogeneous gold- CO2 reduction catalyst counterparts being frequently studied. In this report, a series of N-heterocyclic carbene (NHC)-ligated Au complexes are evaluated in the PCO2RR with an added photosensitizer (tris(2-phenylpyridine)iridium, Ir(ppy)3). The complexes were each studied with and without an added activator used to open a coordination site on the Au complexes. Results show an example of an exceptionally durable PCO2RR catalyst lasting >100 h with high product selectivity for CO. Heterogeneity tests reveal no evidence of a nonhomogeneous active catalyst, and structure-activity relationships of the molecular complexes are discussed

Near-infrared sensitization of solid-state dye-sensitized solar cells with a squaraine dye

Here, we report the use of a squaraine-based dye, JD10, as a near-infrared sensitizer for solid-state dye-sensitized solar cells (ssDSCs). Using spiro-MeOTAD as a hole-transport material, JD10 gave the highest reported power conversion efficiencies (PCE), 3.16% for squaraine-based ssDSCs. The photocurrent was further enhanced by co-sensitization with the organic D-pi-A dye D35, increasing the light harvested leading to a PCE to 4.42%. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4707374

Modulating dye E(S+/S*) with efficient heterocyclic nitrogen containing acceptors for DSCs

Acceptor motifs based on nitrogen containing heterocycles have been synthesized for use in dye-sensitized solar cells (DSCs). Through the selective addition of nitrogen atoms and increased conjugation of the nitrogen containing heterocycles the excited-state oxidation potential, E(S+/S*), may be conveniently tuned with minimal effect on the ground-state oxidation potential, E(S+/S), of the dye

Molecular Au(I) Complexes In the Photosensitized Photocatalytic CO\u3csub\u3e2\u3c/sub\u3e Reduction Reaction

Five Au complexes are evaluated for the reduction reaction of CO2 via cyclic voltammetry and in a photocatalytic system. Electrochemically, the complexes were all evaluated for pre-association with CO2 prior to electrochemical reduction and for thermodynamic favorability for CO2 reduction in photocatalytic systems. The complexes were evaluated in photocatalytic reactions using an Ir-based photosensitizer and a sacrificial electron donor for the conversion of CO2 to CO. Au-complex counterion effects on the photocatalytic reaction were analyzed by varying weakly coordinating counterions with significant performance changes noted. At low Au-complex concentrations, a high TON value of 700 was observed