Unsymmetrical Squaraine Research Articles

Synthesis, spectroscopic characterization and photophysical study of dicyanomethylene-substituted squaraine dyes

Abstract In this work, the synthesis and the photophysical study of novel symmetrical and unsymmetrical squaraine dyes is described. These dyes were prepared by base-catalyzed condensation reaction between 3H-indolium or benzothiazolium salts with dicyanomethylene squarate, derived from squaric acid. The photophysical behavior of the dyes was investigated using UV–Vis absorption and steady-state fluorescence in solution. Additionally, its association with albumin from bovine serum (bovine serum albumin [BSA]) was also investigated. The dyes present strong absorption in the red/infrared regions and fluorescence emission in the infrared region tailored by the electronic structure of the squaraine. Association experiments with bovine serum albumin indicate that the obtained squaraine dyes are suitable for protein detection in solution.

A novel squaraine dye with squaramide as a scaffold and the colorimetric detection of amine

Abstract A novel unsymmetrical squaramide-linked squaraine dye (SQ) has been synthesized through squaramide 3 and semisquaraine 6 . The molecular structure of SQ has been characterized by 1 H NMR, IR and MS. Due to the influence of the hydrogen bond and the solvent effect, SQ exhibits unique spectral properties compared with typical squaraine dyes. For its excellent ability of binding primary amine, SQ is a promising receptor of recognizing primary amine.

Supramolecular assembly of a new squaraine and β-cyclodextrin for detection of thiol-containing amino acids in water

A new unsymmetrical aniline-based squaraine (SQ2) bearing binding unit of Hg2+ ion was designed and synthesised. SQ2 can form 1:2 inclusion complex with β-cyclodextrin, and the resulting complex, which undergoes absorption and fluorescence bleaching upon binding Hg2+, can serve as a turn-on colorimetric or fluorescent chemosensor in organic solvent-free aqueous solution for thiol-containing amino acids with high selectivity and tunable measuring range.

VIS harvesting unsymmetrical squaraine dye for dye-sensitized solar cells

An unsymmetrical squaraine dye which contains an arylamino group was synthesized and used in dye-sensitized solar cells. The molar extinction coefficient of the dye is 77793 M −1 cm −1. Because our synthesized molecule may have no diradical character or the contribution of the diradicaloid component to resonance is quite small, the newly designed squaraine dye has a maximum absorption at 546 nm in the visible region compared with the NIR squaraine sensitizers. Cyclic voltammetry and time dependent density function theory calculation were accomplished to scrutinize the sensitized performance of the dye. Meanwhile, the novel sensitizer has been used to sensitize nanocrystalline TiO 2-based solar cell. Under standard global AM 1.5 solar conditions, the squaraine dye-sensitized cell gives a short circuit photocurrent density ( J SC) of 5.84 mA/cm 2, an open circuit voltage of ( V OC) 0.658 V, and a fill factor (ff) of 0.448, corresponding to an overall conversion efficiency ( η) of 1.72%.

ChemInform Abstract: Efficient and Stable Panchromatic Squaraine Dyes for Dye‐Sensitized Solar Cells.

A new series of stable, unsymmetrical squaraine near-IR sensitizers (JK-216 and JK-217), which are assembled using both thiophenyl pyrrolyl and indolium groups, exhibit a panchromatic light harvesting up to 780 nm. The JK-216 based cell exhibited a record efficiency of 6.29% for near-IR DSSCs. In addition, the JK-217 device showed an excellent stability under a light soaking test at 60 °C for 1000 h.

Efficient and stable panchromatic squaraine dyes for dye-sensitized solar cells

A new series of stable, unsymmetrical squaraine near-IR sensitizers (JK-216 and JK-217), which are assembled using both thiophenyl pyrrolyl and indolium groups, exhibit a panchromatic light harvesting up to 780 nm. The JK-216 based cell exhibited a record efficiency of 6.29% for near-IR DSSCs. In addition, the JK-217 device showed an excellent stability under a light soaking test at 60 °C for 1000 h.

Dual-mode unsymmetrical squaraine-based sensor for selective detection of Hg2+ in aqueous media

A novel chemosensor based on unsymmetrical squaraine dye (USQ-1) for the selective detection of Hg(2+) in aqueous media is described. USQ-1 in combination with metal ions shows dual chromogenic and "turn-on" fluorogenic response selectivity toward Hg(2+) as compared to Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ba(2+), Al(3+), Cu(2+), Cd(2+), Mn(2+), Fe(3+), Ag(+), Pb(2+), Zn(2+), Ni(2+) and Co(2+) due to the Hg(2+)-induced deaggregation of the dye molecule. A recognition mechanism based on the binding mode is proposed based on the absorption and fluorescence changes, (1)H NMR titration experiments, ESI-MS study, and theoretical calculations.

Broad Spectrum Light Harvesting in TiO$_2$ Nanotube Array – Hemicyanine Dye – P3HT Hybrid Solid-State Solar Cells

Control of interfacial electron transfer between electron transporting oxide semiconductors and molecular adsorbates in organic-inorganic hybrid solar cells is a research area of intense interest, with the poor optical harvesting in the red and near-IR (NIR) portion of the solar spectrum a significant limitation to device performance. We fabricate hybrid solar cells, using two new hemicyanine photosensitizers having different π-conjugation lengths that absorb sunlight from visible to NIR range, as well as unsymmetrical squaraine dye. These organic dyes are used not only as a photosensitizer, but also as electronic mediator for n-type TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotube arrays, vertically oriented from the fluorine-doped tin oxide coated glass substrate, which are subsequently infiltrated with p-type regio-regular poly(3-hexyl thiophene 2,5 diyl), enabling broad-spectrum response. In general, the organic-dye-inorganic photovoltaic structure appears a promising method for harvesting a broad portion of the solar spectrum energy from a relatively simple photovoltaic device.

Alkyl and fluoro-alkyl substituted squaraine dyes: A prospective approach towards development of novel NIR sensitizers

Alkyl and fluoroalkyl substituted symmetrical and unsymmetrical squaraine dyes have been synthesized for the fabrication of dye-sensitized solar cells (DSSC) based on nanoporous TiO 2. Results of DSSC performance clearly indicate that introduction of molecular asymmetry and increase in the alkyl chain length of the squaraine sensitizers leads to the enhancement in the photovoltaic performance. A perusal of photo-action spectra of squaraine sensitizer corroborates that introduction of molecular asymmetry and fluoroalkyl substitution leads to hampering of blue-shifted H-aggregate formation. Estimation of energy of HOMO and LUMO for these squaraine sensitizers used in the present investigation indicates that about 0.16 eV is sufficient for electron injection from photoexcited dye to TiO 2 conduction band and dye regeneration.

Molecular Design of Near-IR Harvesting Unsymmetrical Squaraine Dyes

The functionalized unsymmetrical benzothiazole squaraine organic sensitizers 5-carboxy-2-({3-[(3-hexylbenzothiazol-2(3H)-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene}methyl)-1-hexyl-3,3-dimethyl-3H-indolium (hereafter named as SK-11) and 5-carboxy-2-({3-[(3-hexyl-5-methoxybenzothiazol-2(3H)-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene}methyl)-1-hexyl-3,3-dimethyl-3H-indolium (coded as SK-12) are designed and developed to observe an intense and wider absorption band in the red/NIR wavelength region. DFT/TDDFT calculations have been performed on the two unsymmetrical squaraine sensitizers to gain insight into their electronic and optical properties. The utility of these dyes in solid state dye sensitized solar cells (SS-DSSCs) is demonstrated.

Unsymmetrical squaraine dimer with an extended π-electron framework: An approach in harvesting near infra-red photons for energy conversion

A fully conjugated unsymmetrical dimeric squaraine dye was synthesized. The synthetic key step for this dye, a selective Knoevenagel type condensation of end groups to the core moiety, allows the incorporation of a carboxylic acid function essentially for the strong coupling to the titanium dioxide (TiO 2) surface. Moreover, the dimer exhibit outstanding optical properties such as absorption maximum in the NIR region with a huge molar absorption coefficient. The solvatochromic effects were also studied. Furthermore the electrochemical properties were determined with cyclic voltammetry. The reduction potential is just high enough to allow an efficient photo induced charge injection into the conduction band of the TiO 2 semiconductor and the oxidation potential lies about 300 mV below the potential of the iodide / triiodide redox couple providing a good regeneration driving force. From electron density distribution calculations of the optimized BSQ01 structure we could see the directional charge displacement from the solvent exposed side in the HOMO to the carboxyl anchor group in the LUMO. The dimer was immobilised on TiO 2 nanoparticles and a first dye sensitized solar cell was made as a proof-of-concept.

Molecular engineering of panchromatic unsymmetrical squaraines for dye-sensitized solar cell applications

Three unsymmetrical squaraine dyes JK-64, JK-65, and JK-64Hx, containing a bulky spirobifluorene or hexyloxyphenyl unit are designed and synthesized. These sensitizers, when anchored onto a TiO2 surface, exhibit decreased aggregation as well as enhanced unidirectional flow of electrons. Under standard global AM 1.5 solar conditions, an optimized JK-64Hx sensitized cell gave a short-circuit photocurrent density (Jsc) of 12.82 mA cm−2, an open-circuit voltage (Voc) of 0.54 V and a fill factor (ff) of 0.75, corresponding to an overall conversion efficiency (η) of 5.20%.

Visible to Near-Infrared Light Harvesting in TiO2 Nanotube Array−P3HT Based Heterojunction Solar Cells

The development of high-efficiency solid-state excitonic photovoltaic solar cells compatible with solution processing techniques is a research area of intense interest, with the poor optical harvesting in the red and near-IR (NIR) portion of the solar spectrum a significant limitation to device performance. Herein we present a solid-state solar cell design, consisting of TiO(2) nanotube arrays vertically oriented from the FTO-coated glass substrate, sensitized with unsymmetrical squaraine dye (SQ-1) that absorbs in the red and NIR portion of solar spectrum, and which are uniformly infiltrated with p-type regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) that absorbs higher energy photons. Our solid-state solar cells exhibit broad, near-UV to NIR, spectral response with external quantum yields of up to 65%. Under UV filtered AM 1.5G of 90 mW/cm(2) intensity we achieve typical device photoconversion efficiencies of 3.2%, with champion device efficiencies of 3.8%.

Molecular Design of Unsymmetrical Squaraine Dyes for High Efficiency Conversion of Low Energy Photons into Electrons Using TiO2 Nanocrystalline Films

AbstractAn optimized unsymmetrical squaraine dye 5‐carboxy‐2‐[[3‐[(2,3‐dihydro‐1, 1‐dimethyl‐3‐ethyl‐1H‐benzo[e]indol‐2‐ylidene)methyl]‐2‐hydroxy‐4‐oxo‐2‐cyclobuten‐1‐ylidene]methyl]‐3,3‐dimethyl‐1‐octyl‐3H‐indolium (SQ02) with carboxylic acid as anchoring group is synthesized for dye‐sensitized solar cells (DSCs). Although the π‐framework of SQ02 is insignificantly extended compared to its antecessor squaraine dye SQ01, photophysical measurements show that the new sensitizer has a much higher overall conversion efficiency η of 5.40% which is improved by 20% when compared to SQ01. UV‐vis spectroscopy, cyclic voltammetry and time dependent density functional theory calculations are accomplished to rationalize the higher conversion efficiency of SQ02. A smaller optical band gap including a higher molar absorption coefficient leads to improved light harvesting of the solar cell and a broadened photocurrent spectrum. Furthermore, all excited state orbitals relevant for the π–π* transition in SQ02 are delocalized over the carboxylic acid anchoring group, ensuring a strong electronic coupling to the conduction band of TiO2 and hence a fast electron transfer.

Enhancement of Photovoltaic Device Performance in Close-Packed Nanowire Excitonic Solar Cells by Förster Resonance Energy Transfer (FRET)

AbstractOur ability to fabricate close-packed single crystal rutile TiO2 nanowire arrays with average inter-wire distances of 5-10 nm allows us to create and control FRET-induced coupling effects, which can occur in this distance regime, in this architecture. We explored the use of such coupling to boost the performance of nanowire excitonic solar cells. Using Ru complex triplet dye N719 as the energy acceptor and fluorescent tetra tert-butyl substituted zinc phthalocyanine as the energy donor (see Fig. 1 for molecular structures), we obtained up to a four fold improvement in the quantum yield for red photons in the 660-690 nm spectral range. Similarly, by using a carboxylated unsymmetrical squaraine dye as the energy acceptor and highly fluorescent Nile Red dye as the donor (see Fig. 1 for molecular structures), we obtained 60% increased external quantum yields for photons in the 480-580 nm spectral range. For both systems, the use of FRET broadened spectral coverage and improved light harvesting. In this report, we also develop fundamental design principles in choosing donor-acceptor combinations for high efficiency FRET-enhanced solar cells in nanowire array architectures.

Efficient Far Red Sensitization of Nanocrystalline TiO2 Films by an Unsymmetrical Squaraine Dye

An asymmetric squaraine sensitizer comprising an anchoring group was engineered at the molecular level and synthesized. The functionalized novel squaraine sensitizers upon anchoring onto a TiO2 film exhibit an unprecedented incident photon to current conversion efficiency of 85%. The photovoltaic data of this sensitizer using an electrolyte having composition of 0.6 M M-methyl-N-butyl imidazolium iodide, 0.05 M iodine, 0.1 M LiI, 0.05 M tert-butylpyridine in a 15/85 (v/v) mixture of valeronitrile and acetonitrile revealed a short circuit photocurrent density of 10.5 ± 0.2 mA/cm2, an open circuit voltage of 603 ± 10 mV, and a fill factor of 0.71 ± 0.02, corresponding to an overall conversion efficiency of 4.50% under standard AM 1.5 sunlight.

Dye Sensitization of ZnO by Unsymmetrical Squaraine Dyes Suppressing Aggregation

Abstract We have developed an efficient, cyan-colored, and novel squaraine-dye-sensitized ZnO solar cell, producing a maximum incident photon-to-electron conversion efficiency (IPCE) of 59% at 630 nm. The solar cell sensitized by Sq 3 having bulky groups to prevent aggregation of dyes has achieved a 1.5% solar-to-electricity conversion efficiency (η) with a short-circuit current density of 4.04 mA cm−2, an open-circuit photovoltage of 0.61 V, and a fill factor of 0.61 under standard AM 1.5 irradiation (100 mW cm−2).

Synthesis of New Cholesterol- and Sugar-Anchored Squaraine Dyes: Further Evidence of How Electronic Factors Influence Dye Formation

[reaction: see text] Synthesis of new quinaldine-based squaraine dyes linked to cellular recognition elements that exhibit near-infrared absorption (>740 nm) are described. Both product analysis and theoretical calculations substantiate the interesting electronic effects of various substituents in the dye formation reaction. These results are useful in the synthesis of symmetrical and unsymmetrical squaraine dyes that can have potential biological and photodynamic therapeutical applications.

A squaraine-based chemosensor for Hg 2+ and Pb 2+

A novel unsymmetrical cationic squaraine dye ( USqH + ), absorbing in the near-infrared region (600–850 nm), was synthesized by reacting a semi-squaric acid derivative 3-[4-( N, N-dioctylamino)phenyl]-4-hydroxycyclobutene-1,2-dione with the squarylium dye, bis(3-methylbenzothiazol-2-ylidene)squaraine. Addition of micromolar amounts of Hg 2+ and Pb 2+ to solutions of USqH + in dichloromethane brings about significant changes in its absorption spectrum, resulting in a change in colour of the solution from green to pink. The absorption spectrum of the dye is relatively insensitive to other environmentally relevant metal ions, making it possible to visually detect Hg 2+ and Pb 2+ in the presence of other metal ions. Molecular modeling of the complexes at the density functional theory (DFT) and semiempirical PM3 levels strongly suggests that the oxygen atoms are the most likely choice for cation binding. The calculations also indicate a high affinity of Hg 2+ and Pb 2+ toward the formation of 2:1 complexes, which is in good agreement with the experimental results.

Dye sensitization of nanocrystalline TiO 2: enhanced efficiency of unsymmetrical versus symmetrical squaraine dyes

A series of novel symmetrical and unsymmetrical squaraine dyes have been synthesized and their comparative efficiencies as photosensitizers in dye sensitized solar cells (DSSCs) containing nanocrystalline TiO 2 photoelectrodes have been investigated. DSSCs employing unsymmetrical squaraines as sensitizers produced photocurrent with much higher efficiencies compared to DSSCs containing symmetrical squaraines. Aggregation of the dyes on the TiO 2 nanocrystalline electrode was observed to adversely affect the sensitization properties of symmetrical squaraines, whereas efficient sensitization was observed from both the monomeric and aggregated forms of the unsymmetrical squaraines.