Multi-alkylthienyl appended porphyrins for efficient dye-sensitized solar cells

Four porphyrin dyes, incorporating multi-alkylthienyl appended porphyrins as the electron donor, the 2-cyanoacrylic acid as the electron acceptor, and different π-conjugated spacer, have been synthesized for dye-sensitized solar cells (DSSCs). All the porphyrin dyes studied in this work exhibit red-shifted and broadened electronic spectra respect to the reference P_Zn as expected. By the introduction of thienyl groups at the meso-positions, the energy level of E_ox (excited-state oxidation potentials) is significantly shifted to the positive compared with the reference P_Zn, indicating a decreased HOMO–LUMO gap. The highest power conversion efficiency of the four dyes based on DSSCs reached 5.71% under AM 1.5 G irradiation.     

Performance improvement of dye-sensitizing solar cell by semi-rigid triarylamine-based donors

Novel organic dyes (IDB and ISB dyes), which contain 5-phenyl-iminodibenzyl (IDB) and 5-phenyl-iminostilbene (ISB) as electron donors and a cyanoacrylic acid moiety as an electron acceptor and an anchoring group, connected with a thiophene as a π-conjugated system, have been synthesized and used as the sensitizers for dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the dyes were investigated by absorption spectrometry, cyclic voltammetry and density functional theory calculations. As demonstrated, the IDB and ISB unit exhibited stronger electron-donating ability and broader absorption spectra when coated onto TiO₂. The DSSC based on ISB-2 consisting of ISB unit produced 5.83% of η (J_sc = 13.14 mA cm⁻², V_oc = 0.64 V, and ff = 0.68) under 100 mW cm⁻² simulated AM 1.5 G solar irradiation.     

Novel D-π-A system based on zinc porphyrin dyes for dye-sensitized solar cells: Synthesis, electrochemical, and photovoltaic properties

We have designed and synthesized novel zinc porphyrin dyes which have a D-π-A system based on porphyrin derivatives containing a triphenylamine (TPA) electron-donating group and a phenyl carboxyl anchoring group substituted at the meso position of the porphyrin ring, yielding the push-pull porphyrins as the most efficient green dye for dye-sensitized solar cell (DSSC) applications. The synthesis and characterization of a novel D-π-A system based on zinc-porphyrin derivatives have been investigated through their photophysical and photoelectrochemical studies. A large red-shift of the absorption maxima due to introduction of the TPA moiety at the meso position of the porphyrin ring was expected in the D-π-A porphyrins, but the absorption maxima of HKK-Por dyes were a little red-shifted in contrast to Zn[5,-10,15-triphenyl-20-(4-carboxylphenyl)-porphyrin], due to the tilted structure between TPA and the porphyrin unit. Under the photovoltaic performance measurement, the maximum incident photon-to-current conversion efficiency (IPCE) value of the DSSC based on HKK-Por 5 was slightly higher than the efficiencies of the DSSCs based on other HKK-Por dyes due to the introduction of the alkoxy group into the TPA moiety at the meso position of the porphyrin ring. A maximum photon-to-electron conversion efficiency of 3.36% was achieved with the DSSC based on HKK-Por 5 dye (J_SC = 9.04 mA/cm², V_OC = 0.57 V, FF = 0.66) under AM1.5 irradiation (100 m Wcm⁻²).     

Effects of different acceptors in phenothiazine-triphenylamine dyes on the optical, electrochemical, and photovoltaic properties

In dye-sensitized solar cells (DSSCs), as the excited electrons from dye molecules are injected to the conduction band of semiconductor film through the acceptor moieties, the acceptor groups have significant influences on the photovoltaic properties of the dyes. In this paper, the effects of different acceptor groups (cyanoacetic acid and rhodanine-3-acetic acid) in two phenothiazine-triphenylamine dyes (PTZ-1 and PTZ-2) on the optical, electrochemical properties and photovoltaic performances were studied. In comparison with PTZ-2, the photovoltaic performance of PTZ-1 is significantly improved by replacing rhodanine-3-acetic acid to cyanoacetic acid. The conversion efficiency of solar cell based on the PTZ-1 is increased about 110%. The lower efficiency of solar cell based on PTZ-2 is mainly because the delocalization of the excited state is broken between the 4-oxo-2-thioxothiazolidine ring and the acetic acid, which affects the electron injection from PTZ-2 to the conduction band of TiO₂.     

Photovoltaic performance of solid-state DSSCs sensitized with organic isophorone dyes: Effect of dye-loaded amount and dipole moment

Two isophorone sensitizers (S4 and D-3) were utilized in solid-state dye-sensitized solar cells (DSSCs) using spiro-OMeTAD as hole-transporting material. The dye-loaded amount of D-3 was almost 1.5 times as that of S4 which lead to higher light harvesting efficiency than S4. Moreover, the larger dipole moment along the direction for D-3 could cause more negative charges located close to the TiO₂ surface than that of S4, resulting in a larger conduction band (CB) upshift of TiO₂ for D-3 which was beneficial to an increase of V_oc. Promising results sensitized by D-3 in solid-state DSSCs were achieved with a short-circuit photocurrent density (J_sc) of 3.4 mA cm⁻², an open-circuit photovoltage (V_oc) of 760 mV, a fill factor (FF) of 0.71, and an overall efficiency (η) of 1.92% while ruthenium dye N3 produced a η of 2.55% under the same conditions (AM 1.5, 100 mW cm⁻²).     

Alkyloxy substituted organic dyes for high voltage dye-sensitized solar cell: Effect of alkyloxy chain length on open-circuit voltage

Three novel organic dyes (SB1, SB2, and SB3) containing 4-(hexyloxy)-N-(4-(hexyloxy)phenyl)-N-phenylaniline as electron donor and cyanoacrylic acid as electron acceptor bridged by alkyloxy (methyl = SB1, propyl = SB2 and hexyl = SB3) substituted p-phenylenevinylene linkers have been synthesized. Density functional theory (DFT) has employed to study electron distribution and intramolecular charge transfer. Increase in alkyl chain length in alkyloxy substituent leads to increase in open-circuit voltage (V_OC), which is found to be related to the increased electron lifetime at open-circuit condition. Under AM 1.5 G 1 sun light illumination (100 mW/cm²), an optimized SB3-sensitized cell show a short-circuit photocurrent density (J_SC) of 12.83 mA/cm², an open-circuit voltage (V_OC) of 0.745 V and a fill factor (FF) of 0.64, corresponding to an overall conversion efficiency (η) of 6.12%. Little degradation in η observed over 40 days is indicative of long-term stability of the SB-series dyes.     

Polybinaphthyls incorporating chiral (R) or (S)-2,2′-binaphthyland oxadiazole moieties by Stille reaction

Chiral polymers P-1 and P-2 were prepared by the polymerization of (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-1) and (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-1) with 2,5-bis[(4-tributylstannyl)phenyl]-1,3,4-oxadiazole (M-2) via Pd(PPh₃)₄ catalyzed Stille coupling reaction. 1,3,4-Oxadiazole unit not only has high electron affinity, high thermal and oxidative stability, but also serves as a good chromophore. Polymers have strong blue fluorescence due to the efficient energy migration from the extended π-electronic structure of the polymers to the chiral binaphthyl core and can be expected to have potential application in the materials of fluorescent sensors. Circular dichroism (CD) spectra of polymers P-1 and P-2 are almost identical except that they gave opposite signals at each wavelength. The long wavelengths CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and a high rigidity of the polymer backbone.     

Synthesis of new N, N-diphenylhydrazone dyes for solar cells: Effects of thiophene-derived π-conjugated bridge

Four novel D-π-A hydrazone dyes (HT, HM, HE, and HO) with an N, N-diphenylhydrazone moiety as the electron donor, different thiophene-derived π-conjugated bridges and a cyanoacrylic acid moiety as the electron acceptor have been designed and synthesized for the application in dye-sensitized solar cells. The influences of thiophene-derived bridges on the photoelectrochemical and photovoltaic performance of these hydrazone dyes were investigated. Results demonstrate that the introduction of 3,4-dialkyloxythiophene could red-shift the dye’s absorption spectrum due to the enhancement of the electron-donating ability of π-conjugated bridges. Importantly, electrochemical impedance spectroscopy analysis reveal that 3,4-dialkyloxythiophene bridge could change the charge recombination resistance at the TiO₂/dye/electrolyte interface and as a result to improve the open-circuit photovoltage. Among the four dyes, HO exhibits the maximum power conversion efficiency of 5.83% (V_oc = 0.65 V, J_sc = 12.69 mA/cm², FF = 0.707) under simulated AM 1.5 irradiation (100 mW/cm²).     

(R,R)-salen/salan-based polymer fluorescence sensors for Zn detection

(R,R)-salen-based polymer fluorescence sensor P-1 could be synthesized by the polymerization of 5,5′-(isoquinoline-5,8-diylbis(ethyne-2,1-diyl))-bis(3-tert-butyl-2-hydroxybenzaldehyde) (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic addition-elimination reaction, and (R,R)-salan-based polymer sensor P-2 could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence response behaviors of two chiral polymers P-1 and P-2 on Zn²⁺ were investigated by fluorescence spectra. The fluorescence intensities of P-1 and P-2 can exhibit gradual enhancement upon addition of Zn²⁺. Compared with other cations, such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, Cr³⁺ and Pb²⁺, Zn²⁺ can lead to the pronounced fluorescence enhancement as high as 22.8-fold for P-1 and 3.75-fold for P-2, respectively. The results show that P-1 and P-2 incorporating (R,R)-salen/salan moieties as receptors in the polymer main chain backbone can exhibit high sensitivity and selectivity for Zn²⁺ detection.     

Polybinaphthyls incorporating chiral 2,2′-binaphthyl and isoquinoline moieties by Sonogashira reaction

Polymers P-1, P-2, P-3, P-4 and P-5 were synthesized by the polymerization of 5,8-bis(ethynyl)isoquinoline (M-1) with (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-2), (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-2), (R)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-3), (S)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-3), and rac-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl (M-4) under Sonogashira reaction, respectively. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. CD spectra of polymers P-1 and P-2, P-3 and P-4 are almost identical except that they gave opposite signals at each wavelength. The long wavelength CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and the helical backbone in the polymer chain. All five polymers have strong blue-green fluorescence due to the efficient energy migration from the extended π-electronic structure of the repeating unit of the polymers to the chiral binaphthyl core and are expected to provide understanding of structure-property relationships of the chiral conjugated polymers.     

Syndiotactically enriched 1,2-selective polymerization of 1,3-butadiene initiated by iron catalysts based on a new class of donors

A series of phosphoryl (PO) contained compounds: triethylphosphate (a), diethylphenylphosphate (b), ethyldiphenylphosphate (c) triarylphosphates (d and h-m), triphenylphosphine oxide (e), phenyl diphenylphosphinate (f) and diphenyl phenylphosphonate (g) have been prepared. Iron catalysts, which are generated in situ by mixing the compounds with Fe(2-EHA)₃ and AlⁱBu₃ in hexane, are tested for butadiene polymerization at 50 °C. Phosphates donated catalysts have been, unprecedently, found to conduct extremely high syndiotactically (pentad, rrrr = 46.1-94.5%) enriched 1,2-selective (1,2-structure content = 56.2-94.3%) polymerization of butadiene. Introduction of electron withdrawing substituents on phenyl rings oftriphenylphosphate (k-m) remarkably promotes catalytic activity, while bulky substituent isopropyl at 2-position (h) has beneficial influence on regioselectivity. Employment of e, f or g as donor, results in a suppressed monomer conversion, accompanied by deteriorated 1,2-regioselectivity. The effects of polymerization conditions such as reaction temperature, types of cocatalysts and polymerization medium are also investigated by using catalyst system with tri(2,4-difluorophenyl)phosphate (m) as donor. Highly tolerance to polymerization temperature up to 80 °C is observed for the first time in the iron-based catalyst.     

Spectrophotometric investigations and computational calculations of prototropic tautomerism and acid-base properties of some new azo dyes

The prototropic tautomerism in four novel azo compounds derived from pyrazolo[1,5-a]pyrimidin-7(4H)-one was intensively examined. Tautomeric structures which result from annular and azo-hydrazone tautomerism were exposed to semiempirical and density functional theory (DFT) calculations, allowing the recording of structural parameters, physicochemical properties and equilibrium constants to be recorded. The values of the equilibrium constants determined among the most stable forms clearly showed that compounds 1 and 2 co-exist in the NH and hydrazone forms. However, NH tautomers were strongly preferred to other forms in compounds 3 and 4. The observed electronic absorption bands were assigned and compared with the predicted transitions using a time-dependent DFT method (TDDFT). In all solvents employed, except for DMF and acetonitrile, compounds 1 and 2 exhibited azo-hydrazone tautomerism. However, the ionized species were predominant in highly polar solvents for compounds 3 and 4. In DMF, all the investigated dyes exist either in acid-base equilibrium or in the ionized form depending on the molecular structure. Hence, the values of the ionization constant (K_ion) and Gibbs free energy (ΔG) of the equilibrium existing in solution were calculated. In addition, the pK_a values of the investigated dyes were determined spectrophotometrically.     

Synthesis and gas permeation properties of various Si-containing poly(diarylacetylene)s and their desilylated membranes

Diarylacetylene monomers having trimethylsilyl groups and other substituents (substituted biphenyl, 1a and 1b; trimethylsilylmethylphenyl, 1c-e) were synthesized and polymerized with TaCl₅-n-Bu₄Sn catalyst to produce the corresponding poly(diarylacetylene)s (2a-d). Polymers 2a-c had high molecular weights and were soluble in common organic solvents. Free-standing membranes of 2a-c as well as previously reported 2f-h were prepared by the solution-casting method. Desilylation of these Si-containing polymer membranes was carried out with trifluoroacetic acid to afford 3a, 3b, and 3f-h. Upon desilylation, biphenyl-containing membranes became less permeable (3a, b), whereas fluorene-containing membranes became more permeable (3f-h). In particular, 3h exhibited extremely high gas permeability (PO₂ = 9800 barrers), which is about the same as that of poly(1-trimethylsilyl-1-propyne). Desilylated membranes 3a and 3f-h showed different gas permeability from that of polymers 2i-k which have the identical chemical structures and obtained directly by the polymerization of the corresponding monomers.     

Synthesis and characterizations of conjugated copolymers containing benzo[f]isoindole-1,3-dione and diketopyrrolopyrrole units

A weak electron acceptor, 4,9-bis(5-bromothiophen-2-yl)-2-(2-ethylhexyl)-benzo[f]isoindole-1,3-dione (BIDO) was designed and synthesized. Polymer P1 derived from BIDO and 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester by Suzuki cross-coupling reaction has a band gap of 2.41 eV. To expand the absorption range, a different amount of BIDO was copolymerized with a diketopyrrolopyrrole monomer to produce a series of copolymers P_a–c. The optical properties, electrochemical behavior, and energy levels of these four copolymers were investigated. The photovoltaic properties copolymers P_a–c were studied. A photovoltaic device containing P_c and [70]PCBM with a ratio of 1:2 had a power conversion efficiency of 1.17%.     

Synthesis of poly(1-β-naphthyl-2-phenylacetylene) membranes through desilylation and their properties

The polymerization of 1-β-naphthyl-2-[(p-trimethylsilyl)phenyl]acetylene (8a) with TaCl₅-n-Bu₄Sn in cyclohexane provided a high molecular weight polymer (9a) (M_w=3.4×10⁶). The corresponding monomers having p-dimethyl-t-butylsilyl and p-dimethyl(10-pinanyl)silyl groups in place of p-trimethylsilyl group in 8a also polymerized in a similar way to give high molecular weight polymers (9b, 9c, respectively; M_w>1×10⁶). All these polymers were soluble in many common solvents such as toluene and chloroform, and provided free-standing membranes by casting from toluene solution. The oxygen permeability coefficients (P_O2) of 9a at 25 °C was as high as 3500 barrers. The membrane of poly(1-β-naphthyl-2-phenylacetylene) (10a) was prepared by desilylation of the membrane of 9a with trifluoroacetic acid. Polymer 10a was insoluble in any solvents, and showed high thermal stability (the onset temperature of weight loss in air ∼470 °C). The P_O2 value of 10a reached 4300 barrers. Not only the membrane of 9c but also its desilylation product 10c exhibited large optical rotations ([α]_D=+2924 and +9800°, respectively) and strong CD signals. This indicates that the membrane of 10c maintains the helical main chain conformation of 9c with a large excess one-handed helix sense.     

Synthesis of 6-(4-diethylamino)phenyl-2-oxo-2H-pyran-3-carbonitorile derivatives and their fluorescence in solid state and in solutions

One-pot synthesis of a new 2-pyrone dye (3a) by the reaction of 4-diethylamino-acetophenone (1) with methyl 2-cyano-3,3-bis(methylsulfanyl)acrylate (2) in the presence of sodium hydroxide as the base was carried out in DMSO. Compound 4a was synthesized by the replacement of methylsulfanyl group of 3a with dimethylamine at 4-position of pyrone ring. Similarly, compound 5a was prepared via the reaction of 3a with diethyl malonate. Compounds 3a-5a exhibited the following fluorescence in the solid state: red (3a), green (4a), and orange (5a). In addition, it was revealed that 2-pyrone dyes exhibit fluorescence in various solvents and show positive solvatochromism. Compounds 3a and 5a exhibited intense fluorescence in chloroform and dichloromethane (fluorescence quantum yield Φ: 0.94-0.95). In contrast, compound 4a exhibited intense fluorescence in polar solvents (methanol: Φ = 0.92). These 2-pyrone dyes have the potential for applications in various fields.     

The synthesis, spectroscopic properties and crystal structures of some rhodanine merocyanine dyes for optical recording with a blue diode laser

Six rhodanine merocyanine dyes were synthesized via both a conventional solvent method and a microwave method using rhodanine, 2-methylthio quaternary salts and 1H-indole-3-carbaldehyde as starting materials. The products were identified using UV-Vis, IR, MS, ¹H NMR and elemental analysis. The UV-Vis absorption spectra of the dyes in chloroform, DMSO, water, acetone, ethanol and methanol were investigated. The structures of two dyes (5a and 5b) were characterized and analyzed by X-ray diffraction as well. Crystallographic data revealed that dye 5a belonged to tetragonal, I4 (1)/a space group, while dye 5b belonged to monoclinic, P-1 space group. In the case of both dyes, intermolecular associations occurred by π-π stacking and intermolecular hydrogen bonds, which contributed to stabilize the crystal structure.     

Synthesis and application of H-Bonded cross-linking polymers containing a conjugated pyridyl H-Acceptor side-chain polymer and various carbazole-based H-Donor dyes bearing symmetrical cyanoacrylic acids for organic solar cells

A series of novel hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating carbazole cores bearing symmetrical thiophene linkers and cyanoacrylic acid termini with a proton-acceptor (H-acceptor) side-chain homopolymer carrying pyridyl pendants (with 1/2 M ratio of H-donor/H-acceptor). The supramolecular H-bonded structures between H-donor dyes and the H-acceptor side-chain polymer were confirmed by FTIR measurements. The effects of the supramolecular architecture on optical, electrochemical, and organic photovoltaic (OPV) properties were investigated. From DFT (density functional theory) calculations, the optimized geometries of organic dyes reflected that the carbazole cores of H-donor dyes were coplanar with the conjugated thiophenes and cyanoacrylic acids, which is essential for strong conjugations across the donor-acceptor units in D1-D4 dyes. Under 100 mW/cm² of AM 1.5 white-light illumination, bulk heterojunction (BHJ) OPV cell devices containing an active layer of H-bonded polymers (PDFTP/D1-D4) as an electron donor blended with [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) as an electron acceptor in a weight ratio of 1:1 were explored. From the preliminary investigations, the OPV device containing 1:1 weight ratio of H-bonded polymer PDFTP/D2 and PCBM showed the best power conversion efficiency (PCE) value of 0.31% with a short-circuit current (J_sc) of 1.9 mA/cm², an open-circuit voltage (V_oc) of 0.55 V, and a fill factor (FF) of 29%, which has a higher PCE value than the corresponding H-donor D2 dye (PCE = 0.15%) or H-acceptor PDFTP homopolymer (PCE = 0.02%) blended with PCBM in 1:1 weight ratio.     

Synthesis, characterization, and high gas permeability of poly(diarylacetylene)s having fluorenyl groups

Diarylacetylenes having fluorenyl groups and other substituents (trimethylsilyl, t-butyl, bromine, fluorine) (1a-1) were polymerized with TaCl₅-n-Bu₄Sn. Monomers 1a-l produced high molecular weight polymers 2a-l (M_w 5.1 × 10⁵-1.3 × 10⁶) in 12-59% yields. All of the polymers were soluble in common organic solvents, and gave tough free-standing membranes by the solution casting method. The onset temperatures of weight loss of polymers 2a-l in air were over 400 °C, indicating considerably high thermal stability. All the polymer membranes showed high gas permeability; e.g., the oxygen permeability coefficient (PO₂) of 2a was as large as 4800 barrers. Membrane 2d possessing two fluorine atoms at meta and para positions of the phenyl ring showed the highest oxygen permeability (PO₂ = 6600 barrers) among the present polymers.