SQ Dyes Research Articles

Structural, optical spectroscopic, and density functional theory calculations of squaraine dye for organic electronic applications

The structural, optical spectroscopic, and density functional theory calculations of 2,4-Bis[4-(N,N-diisobutylamino)−2,6-dihydroxyphenyl] squaraine dye (SQ) are promising investigations that can be useful in photochemical mechanisms explanation and in designing promising chemosensors. The nature of the bonds, the chemical composition of SQ, crystallographic structure, morphology, and quality characteristics were explored by FTIR, XRD, and SEM investigations. The crystallite size, the dislocation density, and the lattice strain were found to be 57.3 nm, 3.045 × 10−4 nm−2, and 3.065 × 10−3, respectively. The spectrum behavior of the absorbance and molar absorption coefficient spectra of SQ in DCM with three concentrations were analyzed to get some important optical properties of SQ dye. The determined optical gap transition equals Egapopt=1.81eV. Quantum chemical computations and optimized molecular geometries identified where electrophilic attacks are likely and analyzed the molecule’s electrostatic potential. Using DFT calculations at the B3LYP/6-31+G(d,p) level, the electronic structure of the squaraine molecule was confirmed, showing a HOMO–LUMO gap of 1.73 eV. MEP analysis indicated that the oxygen atoms are electron-rich, suggesting potential for hydrogen bonding and electrophilic interactions.

Squaraine-loaded mesoporous silica nanoparticles for antimicrobial Photodynamic Therapy against bacterial infection

Antimicrobial photodynamic therapy (aPDT) shows promise as a complementary or alternative approach to conventional antimicrobial treatments. Despite possessing some key advantages, many challenges remain, such as optimizing the delivery of photosensitizers, improving light penetration into tissues, and determining the most effective combinations of photosensitizers and light wavelengths for different infections. Moreover, addressing the challenges associated with the aggregation tendency and poor solubility of some photosensitizers, squaraine dyes (SQs) in particular, is crucial for unlocking their full potential in biomedical applications.This contribution focuses on designing innovative nanophotosensitizers with antimicrobial properties using mesoporous silica nanoparticles (MSNs) loaded with a SQ dye (i.e. Br-SQ). MSNs before and after Br-SQ loading were deeply characterized using different techniques, proving the successful incorporation of the dye into the nanocarriers. Upon visible light (640 nm) irradiation, these nanosystems demonstrated remarkable antibacterial activities against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli).Our results confirmed that MSNs are valuable nanocarriers of hydrophobic photosensitizers, such as Br-SQ, bringing up new opportunities to develop antibiotic-free nanoformulations to treat bacterial infection while minimizing the risk of antimicrobial resistance.

Annealing effect on the morphology, linear and non-linear optical properties of squaraine derivative thin films for optoelectronics applications

Squaraine is a class of organic compounds that possess unique optical properties, including strong absorption of light, high fluorescence quantum yields, etc. Here, we explore the structural and spectroscopic investigations of 2,4-Bis[4-(N,N-dibenzylamino)-2,6 dihydroxyphenyl] squaraine dye (SQ) under different conditions of thermal effects. The molar absorptivity (εmolar) spectra were used to describe the electric dipole strength (q2) and the oscillator strengths (f) of SQ dye. The Surface morphology of SQ dye was investigated by AFM and the average roughness shows dependence on the annealing effect. A slight change in the optical energy gap (⁓ 0.3 eV) after annealing up to 473 K reflects the optical stability of our investigated thin films. The optical band transitions and photoluminescence (PL) emission spectra were described before and after annealing at 423 & 473 K. As the temperature annealing film increased to 473 K, the nonlinear parameters such as χ(3) and n2 decreased by about 44% and 36%, respectively. The good thermal stability, suitable optical band gap, and refractive index offer potential applications as active photonic materials in photonic/optoelectronic applications.

Synthesis of Highly Photostable Benzoindolenine‐Based Squaraine Dyes by using Aromatic Fluorine Atoms

AbstractWe have elucidated the details of the photodegradation of non‐fluorinated benzoindolenine‐based SQ dyes with low photostability in solution and proposed a hypothesis to improve their photostability. Based on the results, replacing all the hydrogen atoms on the benzoindolenine ring with fluorine atoms or methylation of the oxygen anions of the non‐fluorinated benzoindolenine SQ dye resulted in improvement of photostability. Furthermore, a preliminary investigation of the synthesized SQ dyes for organic photovoltaics revealed that the O‐methylated SQ dye with bulky fluorine‐containing anions provided a much higher Voc than similar benzoindolenine‐based SQ dyes.

Shortwave infrared-absorbing squaraine dyes for all-organic optical upconversion devices

ABSTRACT Shortwave infrared (SWIR) optical sensing and imaging are essential to an increasing number of next-generation applications in communications, process control or medical imaging. An all-organic SWIR upconversion device (OUC) consists of an organic SWIR sensitive photodetector (PD) and an organic light-emitting diode (OLED), connected in series. OUCs directly convert SWIR to visible photons, which potentially provides a low-cost alternative to the current inorganic compound-based SWIR imaging technology. For OUC applications, only few organic materials have been reported with peak absorption past 1000 nm and simultaneous small absorption in the visible. Here, we synthesized a series of thermally stable high-extinction coefficient donor-substituted benz[cd]indole-capped SWIR squaraine dyes. First, we coupled the phenyl-, carbazole-, and thienyl-substituted benz[cd]indoles with squaric acid (to obtain the SQ dye family). We then combined these donors with the dicyanomethylene-substituted squaraine acceptor unit, to obtain the dicyanomethylene-functionalized squaraine DCSQ family. In the solid state, the absorbance of all dyes extended considerably beyond 1100 nm. For the carbazole- and thienyl-substituted DCSQ dyes, even the peak absorptions in solution were in the SWIR, at 1008 nm and 1014 nm. We fabricated DCSQ PDs with an external photon-to-current efficiency over 30%. We then combined the PD with a fluorescent OLED and fabricated long-term stable OUCs with peak sensitivity at 1020 nm, extending to beyond 1200 nm. Our OUCs are characterized by a very low dark luminance (<10−2 cd m−2 at below 6 V) in the absence of SWIR light, and a low turn-on voltage of 2 V when SWIR light is present.

Discrete photoelectrodes with dyes having different absorption wavelengths for efficient cobalt-based tandem dye-sensitised solar cells

A pn-tandem dye-sensitised solar cell (pn-DSSC) employing a set of sensitisers with complementary absorption spectra and a less-corrosive cobalt-based electrolyte is presented. We applied three organic sensitisers (denoted C343, DCBZ, and SQ) featuring different absorption wavelengths for the p-DSSC, while keeping the n-DSSC sensitiser (denoted DCA10CN2) constant. Characterisation of the Co+2/+3-based DSSC devices revealed that SQ dye, with a longer absorption wavelength, showed broader spectra and increased photocurrent activity in the visible and near-infrared region compared to the other two devices with C343 and DCBZ in the pn-DSSCs. As a result, the short-circuit current density increased significantly to 4.00 mA cm−2, and the devices displayed overall power conversion efficiencies of as high as 1.41%, which is comparable to that of the best pn-DSSCs in the literature. Our results demonstrate that complementary absorption between the two photoelectrodes is important for enhancing the photovoltaic performance of pn-DSSCs.

Extending spectrum response of squaraine-sensitized solar cell by Förster resonance energy transfer

To extend the spectral response region of squaraine dye (SQ)-sensitized solar cell, eosin Y (EY) is encapsulated in the SQ-sensitized nanocrystalline thin film. EY is first adsorbed on nanocrystalline TiO2 thin film (n-TiO2), then a thin layer of EY contained ZnO (EY-ZnO) is electrodeposited, and SQ dye is finally sensitized to form two dye-sensitized nanocrystalline thin film with a structure of n-TiO2/EY/EY-ZnO/SQ. There is a perfect spectral overlap between the emission of EY and the absorption of SQ; EY as an energy donor simultaneously transfers both electron and hole to the energy acceptor SQ according to the Forster resonance energy transfer (FRET) process. EY shifts the spectral response edge of SQ-sensitized solar cell toward blue from 550 to 450 nm through the FRET process in this new structure. Two dye-sensitized nanocrystalline thin film demonstrates a significant enhancement in light harvesting and photocurrent generation due to the FRET process. The thickness of the EY-ZnO thin layer and spectral overlap between emission of donor dye and absorption of acceptor dye are two important factors that affect the FRET process between EY and SQ in the structure of n-TiO2/EY/EY-ZnO/SQ.

Application of CBZ dimer, C343 and SQ dye as photosensitizers for pn-tandem DSCs

A pn-tandem dye-sensitized solar cell (pn-DSC) was prepared with three different sensitized dyes CBZ Dimer (CBZD), C343, and SQ in two different compartments of the n-type or p-type cells. The constructed tandem solar cell was exhibited considerable improvement in experimental pn-DSCs parameters, open-circuit voltage, short-circuit current, fill factor, etc. These results were achieved under air mass 1.5 illumination with three different sensitized dyes in the upper and lower compartment of the pn-DSCs. These results demonstrate a complementary absorption among the two photoelectrodes in the pn-DSCs is a good approach to the efficient and low cost pn-DSCs.

Panchromatic and High-efficient Energy Transfer Assembly Based on Type I Core-shell Quantum Dots

In order to overcome the low energy transfer efficiency of the conventional FRET (Forster resonance energy transfer) system, a novel spectra-matching and distance-controllable CIS@ZnS-SQ FRET assembly has been prepared via ultrasonic self-assembly method, by using the synthesized visible CIS@ZnS type I core-shell quantum dots as energy donor and the near infrared SQ dyes as acceptor. Through controllable synthesis of quantum dots, the absorption and fluorescence performance of FRET system were adjusted by the size of CIS@ZnS, while the distance of energy donor-acceptor and the non-valid charge recombination in the FRET system were controlled by the wide-band shell of quantum dots. The excitons transfer and recombination kinetics in CIS@ZnS-SQ assembly were investigated by the pump-probe femtosecond ultrafast transient absorption measurements, with which results in the FRET-type energy transfer mechanism: CIS*+SQ→CIS+SQ* has been proven and a high energy transfer rate of about 5.0×10 s has been gained between CIS@ZnS and SQ. The excitons’ lifetime and FRET energy transfer efficiency were calculated from the fluorescence decay kinetic curves tested by time-resolved fluorescence measurements. The results show that the energy transfer in CIS@ZnS-SQ depends on the size of CIS@ZnS quantum dots. As the size of CIS@ZnS (mainly refers to the ZnS shell thickness) increases from 2.1±0.4 nm to 2.9±0.4 nm, 4.1±0.3 nm, 5.4±0.5 nm and 7.2±0.5 nm, the fluorescence quantum yield of CIS@ZnS improves from 5.4% to 26%, 33%, 38% and 43.3% as well as the distance between CIS@ZnS and SQ (energy donor and acceptor) increases gradually, which makes the FRET energy transfer efficiency (ηFRET) first rise and then decline. As a result, an optimal ηFRET value of 62.8% was gained in the FRET assembly when the reaction time of ZnS shell was 20 min. This research will have a promising theoretical and practical value for the development of the panchromatic and high-efficiency solar cells.

The Preparation and Photovoltaic Properties of Quasi-solid State Dye-Sensitized Solar Cells Containing Long Wavelength Absorbing Squaraine Dye

The performance of the quasi-solid state DSSC composed of long wavelength absorbing squaraine dye was investigated and compared with that of ruthenium-complex (N3) sensitized DSSC. In spite of the narrow sensitizing region of SQ dye from 500 nm to 750 nm, the quasi-solid state DSSCs gave a moderate solar energy-to-electricity conversion efficiency under AM 1.5 G irradiation (100 mW/cm2) of 2.34%, a short-circuit current density of 5.56 mA/cm2, with an open-circuit voltage of 650 mV.

DFT studies of squarylium and core‐substituted squarylium dye derivatives: understanding the causes of the additional shorter wavelength absorption in the latter

Recent reports indicate that the core‐substituted squarylium (CSQ) dyes (obtained when one oxygen atom of the SQ moiety is replaced by an electron withdrawing group or sulfur) show bathochromic shift of the absorption maxima and an additional shorter wave length absorption in visible when compared to parent SQ dyes. To investigate this interesting property of these dyes which will be more suitable for applications in DSSC, a comparative study using computational techniques of some selected SQ and CSQ derivatives has been carried out. The effect of this core substitution on geometries is studied. The ground state charge distribution is analyzed by natural population analysis. It is noticed that the biradical character, which is normally large in SQ derivatives, is reduced in CSQ due to the substitution and the zwitterionic character is increased. The absorption maxima for both parent SQ and CSQ dyes obtained with TD‐DFT methods using various functional like B3LYP, M06‐2X and CAM‐B3LYP methods do not match the experimental results. However, results obtained using SAC‐CI method are better. Charge transfer (CT) data based on Mulliken charges of both ground and excited states is obtained from SAC/SAC‐CI studies. It is seen that on excitation substantial CT from the side groups to the central core is taking place in parent SQ molecules. In contrast, intense CT occurs from –X to side groups through central core in the case of CSQ molecules. This study will be helpful in designing and synthesizing new CSQ dyes which makes them suitable for solar cell applications. Copyright © 2012 John Wiley &amp; Sons, Ltd.

ChemInform Abstract: Synthesis of Novel Unsymmetrical Squarylium Dyes Absorbing in the Near-Infrared Region.

Novel unsymmetrical squarylium dyes which absorb in the near-infrared region were synthesized by a stepwise procedure via intermediate 4-substituted 3-hydroxycyclobut-3-ene-1,2-diones. By introducing benz[c,d]indoline or benzo[b]pyran moieties at one end as an electron-donating component, the SQ dyes exhibited their absorption maxima at 739–821 nm with large molar absorption coefficients (log e = 4.96–5.18) in CHCl3. The X-ray analysis for one of these dyes was also examined to confirm the overall structure of the unsymmetrical SQ dye.

High-level computational studies of Rhodizonate derivatives: Molecules absorbing in near infrared region due to larger C–C–C angle of the oxyallyl ring

Oxyallyl derivatives Croconate dyes (CR) and Squarylium dyes (SQ) are well-known near infrared (NIR) dyes and in general have been considered to be Donor–Acceptor–Donor type molecules with CR dyes absorbing in the longer wavelength region when compared to the corresponding SQ dyes. Recent high-level calculations have shown conclusively that the NIR absorption in these molecules is not due to the increased donation and acceptance but is due to the diradicaloid nature of the central oxyallyl ring. In continuation of our work on oxyallyl derivatives, we extend the studies to a larger central ring; Rhodizonate (RH) with different substitutions and carry out high-level symmetry-adapted cluster-configuration interaction (SAC-CI) calculations. From the calculations it is predicted that derivatives of RH absorb in the longer wavelength region than the corresponding SQ and CR. We show that the charge transfer is very small and does not play the key role in the red shift but on the other hand it is the perturbation of the HOMO–LUMO gap (HLG) and the diradicaloid nature both due to geometry and substitution, which seem to be responsible for this shift. We reiterate the design principle that increasing the donor capacity of the groups may not help in the red shift, but introducing groups which perturb the HLG and decrease it without changing the MO character should lead to a larger bathochromic shift. We conclude that these RH dyes with absorption greater than 1000 nm will find applications as nonlinear optical (NLO) materials and functional dyes.

Near-Infrared Absorption in Symmetric Squarylium and Croconate Dyes: A Comparative Study Using Symmetry-Adapted Cluster-Configuration Interaction Methods

Symmetric croconate (CR) and squarylium dyes (SQ) are well-known near-infrared (NIR) dyes and, in general, are considered to be donor-acceptor-donor type molecules. It is established in the literature that CR dyes absorb in a longer wavelength region than the corresponding SQ dyes. This has been attributed to the CR ring being a better acceptor than the SQ ring. Thus increasing the donor capacity should lead to a bathochromic shift in both SQ and CR. On the other hand, some experiments reported in the literature have revealed that increasing the conjugation in the donor part of the SQ molecule leads first to red shift, which upon a further increase of the conjugation changes to a blue shift. Hence, to understand the role of the central ring and the substitutions in the absorption of these dyes, we carried out high-level symmetry-adapted cluster-configuration interaction (SAC-CI) calculations of some substituted SQ and CR dyes and compare the absorption energy with the existing experimental data. We found that there is very good agreement. We also carried out SAC-CI calculations of some smaller model molecules, which contain the main oxyallyl substructure. We varied the geometry (angle) of the oxyallyl subgroup and the substitution in these model molecules to establish a correlation with the bathochromic shift. We found that the charge transfer is very small and does not play the key role in the red shift, but on the other hand, the perturbation of the HOMO-LUMO gap (HLG) from both the geometry and substitution seems to be responsible for this shift. We suggest as a design principle that increasing the donor capacity of the groups may not help in the red shift, but introducing groups which perturb the HLG and decrease it without changing the MO character should lead to a larger bathochromic shift.

Photoreaction and photopolymerization studies on squaraine dyes/iodonium salts combination

A novel visible photosensitized system, squaraine dye (SQ)/iodonium salt (On) combination, used as a radical photogeneration source has been suggested and studied. The thermodynamic data and experimental results show that the SQ/On combination readily undergoes photoreaction via fast intramolecular ion-pair electron transfer within the short time scale of excited lifetime of SQ, simultaneously resulting in a photobleaching of SQ dye and a generation of active radical species released by subsequent decomposition of onium product. Some important factors that affect the formation of ion-pair complex between SQ dye and onium salts, such as solvent polarity, nature of counter anion, concentration of SQ dye and onium salt, show a large influence on the photoreaction kinetics. Based on the results of primary photoreaction, the visible photopolymerization using SQ/On combination as photoinitiator was studied in the solution and film. The synchronous photopolymerization and photobleaching behaviors were found in the polymerization process. The dye-sensitized photoreaction mechanism of SQ/On system was also proposed and discussed.

Synthesis of novel unsymmetrical squarylium dyes absorbing in the near-infrared region †

Novel unsymmetrical squarylium dyes which absorb in the near-infrared region were synthesized by a stepwise procedure via intermediate 4-substituted 3-hydroxycyclobut-3-ene-1,2-diones. By introducing benz[c,d]indoline or benzo[b]pyran moieties at one end as an electron-donating component, the SQ dyes exhibited their absorption maxima at 739–821 nm with large molar absorption coefficients (log e = 4.96–5.18) in CHCl3. The X-ray analysis for one of these dyes was also examined to confirm the overall structure of the unsymmetrical SQ dye.

TiO2-Assisted Photodegradation of Dyes. 9. Photooxidation of a Squarylium Cyanine Dye in Aqueous Dispersions under Visible Light Irradiation

The TiO2-assisted photodegradation of a squarylium cyanine dye (SQ) has been examined under visible light irradiation (λ ≥ 430 nm) by UV−vis, proton-NMR, ESR, and GC-MS spectroscopies, by peroxide assays in the presence of peroxidase and catalase enzymes, and by chemical oxygen demand (COD) methods. Significant results were obtained relevant to the mechanism(s) of TiO2-assisted photodegradations. The active oxygen species produced first when an aqueous TiO2 dispersion containing SQ is irradiated by visible light is the superoxide radical anion, which is stable in methanol solvent but very unstable in aqueous media, and is readily converted to •OH radicals via formation and subsequent reduction of H2O2. The quantity of H2O2 increased during the photodegradation; though expected, no organoperoxides were detected. Of import, cleavage of the cyanine CC double bond in the SQ dye dominated over the whole degradation process yielding 1-sulfopropyl-3,3-dimethyl-5-bromoindolenium-2-one, the predominant component i...

Syntheses, characteristics and electrophotographic properties of new dithiosquarylium dyes

A new class of dithiosquarylium dyes (DTSQ) has been synthesized by the reaction of squarylium dye (SQ) with Lawesson's reagent or P 4S 10. The λ max , of DTSQ dyes undergoes a bathochromic shift of about 25 nm compared with corresponding SQ dyes. The visible absorption spectra of DTSQ dyes are well accounted for by Pariser-Parr-Pople Molecular Orbital (PPP-MO) calculations. Electrophotographic characteristics of negatively charged dual layered photoreceptors with DTSQ for charge generation materials (CGM) and 1-phenyl-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1′,1′-diphenylhydrazone as a charge transport material (CTM) have been investigated. The photoreceptor that used DTSQs exhibited high photosensitivity at white light.

Synthesis and Absorption Spectral Shifts of Novel Squarylium Dyes.

Two kinds of new squarylium dyes have been prepared. Aminosquarylium dyes (ASQ) (6) have been prepared by condensation of aminosquarates (3) and 1-ethyl-2,3,3-trimethylindolenium iodide (5). New aminosquarylium dye 6a absorbed at a longer wavelength (18 nm) than the corresponding squarylium dye (SQ) 7c. A new class of dithiosquarylium dyes (DTSQ 8) has also been synthesized by the reaction of squarylium dye (SQ) with Lawesson's reagent or P 4 S 10 . The λ max of DTSQ dyes undergoes a bathochromic shift of about 25 nm compared with.corresponding SQ dyes. The visible absorption spectra of ASQ and DTSQ dyes are well accounted for by PPP-MO calculations.