Study of absorption and emission spectra of substituted terthiophene compounds by methods of theoretical chemistry.

Terthiophene derivatives attract interest due to their prospective applications in optoelectronic or sensor devices. Due to their nontoxicity they can be considered as suitable candidates in biological applications. Supramolecular organization of the matter is one of the most interesting topics in contemporary materials science. Amphiphilic chromophores based on substituted terthiophenes are capable of self-assembly into supramolecular architectures. In this work, we aim at simulation of the spectral properties of terthiophene with oligo(ethylene oxide) substituents by the methods of quantum chemistry and molecular dynamics (MD). The potential energy surface (PES) of this molecule was determined by the methods of density functional theory (DFT) for the ground state and time-dependent density-functional theory (TD-DFT) for the excited state. MD simulations in water than revealed the most frequented molecular conformations in both these states. Absorption and fluorescence spectra were determined for all these conformations, including the surrounding water molecules, using TD-DFT and averaged over the conformation space to obtain the final absorption and fluorescence spectrum. The calculated spectra were compared with their experimental counterparts and the differences were discussed in context of the supramolecular structure revealed by confocal microscopy. In spite of its simplicity, this approach provides a satisfactory approximation of absorption and fluorescent spectra of these molecules obtained by computational methods.

Investigating the Properties of Triangle Terthiophene and Triphenylamine Configured Propeller-like Photochromic Dye with Ethyne Bridge.

Synthesis-oriented design led us to the construction of a propeller-like dye, containing the triangle terthiophene and triphenylamine units. It reveals typical photochromic properties with alternated UV (390 nm) and visible light (˃ 440 nm) irradiation and the dye solution (in THF) color was also toggled between yellow-green and colorless. A new absorption band was observed in visible region (415-600 nm). Additionally, the photochromic dye was highly emissive with the absolute quantum yield being 0.27. After UV light irradiation, the emission was quenched significantly (Φ = 0.08) at photo-stationary state, and thus establishing a switchable emission "on-off" system by alternated UV/visible light irradiation cycle. Detailed structural analysis was carried out based on the optimized dye structure. Both the antiparallel conformation and the distance of reactive carbon atoms (< 4.2 Å) led to the smoothly photochromic behavior.

Investigation of Triangle Terthiophene and Hydroxyphenylbenzothiazole Configured Fluorescent Dye with a Triple Bond Bridge.

A photochromic dye was constructed by incorporation of a carbon-carbon triple bond spaced triangle terthiophene skeleton and hydroxyphenylbenzothiazole. Regular photochromic behavior was investigated with alternated UV (254 nm) and visible light (≥ 400 nm) irradiation. The color of dye in solution can be cycled between pink and colorless. Additionally, the dye solution strongly fluoresces in THF with the absolute quantum yield (QY) being 0.56. When irradiation with 254 nm light, the emissive solution can be effectively quenched to photo-stationary sate (Φ = 0.05). An emission "on-off" cycle could be established based on the UV/visible light irradiation cycle. The photochromic dye also exhibits good photo- and thermal-stability at room temperature. The emission decay profile indicates typical single component character with the fluorescence lifetime being 6.68 ns. The emission color was determined by the CIE 1931 coordinates of x = 0.14, y = 0.25 in the blue region.

Photo-Induced Fluorochromism of a Star-Shaped Photochromic Dye with 2,4-Dimethylthiazole Attaching to Triangle Terthiophene.

A photochrmic triangle terthiophene dye with 2,4-dimethylthiazole attached was synthesized and shows regular photochromic properties when irradiated with UV/Vis light alternately. It was found that the attaching of 2,4-dimethylthiazole has a significant effect on both the photochromism and fluorescence of triangle terthiophene. During the photocyclizatioin prcess, not only the color but also the fluorescence of the dye in THF can be toggled between ring-open and ring-closed forms of the dye. Additionally, the absolute quantum yields (AQY) of ring-open and ring-closed forms of the dye (0.32/0.58) were greatly larger than the literature report. Along with the 254 nm light irradiation, the fluorescence color changed from deep blue (428 nm) to sky blue (486 nm) in THF. A fluorochromism cycle could be established based on the UV/visible light irradiation cycle, which provides a strategy for the design of new type fluorescent diarylethene derivatives for biological application.

Investigating the Properties of Double Triangle Terthiophene Configured Dumbbell-Like Photochromic Dye with Ethyne and 1,3-Butadiene Bridge.

Dumbbell-like photochromic dyes were constructed by incorporation of double triangle terthiophene with ethyne or 1,3-butadiene bridge. Regular photochromic behavior was investigated with alternated UV (365 nm) and Visible light (˃ 400 nm) irradiation. However, the different bridge group leads to distinct difference in their photochromic wavelength. For the ethyne bridged triangle terthiophene (DT1), the photochromic wavelength was observed around 500-700 nm (peak value: 605 nm) and the solution turned to red with 365 nm light irradiation. However, the photochromic wavelength was blue shift to 418-550 nm and the solution was turned to light yellow for 1,3-butadiene bridged dye (DT2). Both of the colored solution can be bleached via visible light irradiation. Additionally, the two dyes in THF were emissive with absolute quantum yield (QY) of 0.36/0.40. Along with the photo-induced photocyclization process, the emissive solution can be effectively quenched at photo-stationary sate (Φ = 0.05/0.04). And emission "on-off" cycle could be established based on the UV/visible light irradiation cycle.

Insight into Unusual Supramolecular Self-Assemblies of Terthiophenes Directed by Weak Hydrogen Bonding.

A supramolecular self-assembly of semiconducting polymers and small molecules plays an important role in charge transportation, performance, and lifetime of an optoelectronic device. Tremendous efforts have been put into the strategies to self-organize these materials. In this regard, here, we present the self-organization of terthiophene and its methyl alcohol derivative with 4,4'-bipyridine (44BiPy). An unexpected 2D layered organization of 5,5″-dimethyl-2,2':5',2″-terthiophene (DM3T) and 44BiPy was obtained and analyzed. Single-crystal X-ray diffraction analysis revealed that DM3T and 44BiPy consist of stacked, almost independent, infinite 2D layers while held together by weak hydrogen bonds. In addition to this peculiar supramolecular arrangement of these compounds, the investigation of their photophysical properties showed strong fluorescence quenching of DM3T by 44BiPy in the solid state, suggesting an efficient charge transfer. On the other hand, the methyl alcohol derivative of terthiophene, DM3TMeOH, organized in a closed cyclic motif with 44BiPy via hydrogen bonds.

Terthiophene-functionalized mesoporous silica-based fluorescence sensor for the detection of trace methyl orange in aqueous media.

A terthiophene-functionalized mesoporous SBA-15 silica, i.e., TTU-SBA-15, was successfully developed and used as a highly selective and ultrasensitive fluorescence sensor for methyl orange (MO) detection. When the concentration of MO was increased, the fluorescence emission intensity of TTU-SBA-15 suspensions at 452 nm gradually decreased at an excitation wavelength of 368 nm, and the color of the suspension solutions changed obviously from blue to dark under 365 nm UV light. The fluorescence intensity at 452 nm was linearly proportional to the concentration of MO in the range 0.20 - 2.0 µM, with a detection limit of 0.092 µM. Competitive pollutants, variations in pH, and sample recycling had subtle or negligible effects on the detection of MO. TTU-SBA-15 was applied to the determination of MO in tap water, and recoveries from spiked samples were in the range 98.3 - 103.0%. This study provides a convenient and effective strategy to realize highly sensitive and selective sensors that could target dyes via the functional modification of mesoporous materials.

Magnetism and Luminescence of a MOF with Linear Mn3 Nodes Derived from an Emissive Terthiophene-Based Imidazole Linker.

A new terthiophene-based imidazole luminophore 5,5'-(1H-thieno[3,4-d]imidazole-4,6-diyl)bis(thiophene-2-carboxylic acid) (TIBTCH2, 5) was synthesized in one step from previously reported 4,6-di(thiophen-2-yl)-1H-thieno[3,4-d]imidazole (DTTI, 4), and their photophysical properties were studied and compared accordingly. Under solvothermal conditions, reacting 5 with Mn(OAc)2 yielded a new three-dimensional metal-organic framework (MOF, 6) which was structurally defined by single-crystal X-ray diffraction. In 6, all Mn(II) ions octahedrally bind to carboxylate-O atoms to form a linear Mn3 secondary building unit (SBU) that contains three distinct coordination modes. Importantly, 6 exhibits dual functional properties of ligand-based emission and metal-based magnetic behaviors.

Wavelength-Dependent Singlet Oxygen Generation in Luminescent Lanthanide Complexes with a Pyridine-Bis(Carboxamide)-Terthiophene Sensitizer.

Lanthanide ion (LnIII ) complexes, [Ln(3Tcbx)2 ]3+ (LnIII =YbIII , NdIII , ErIII ) are isolated with a new pyridine-bis(carboxamide)-based ligand with a 2,2':5',2''-terthiophene pendant (3TCbx), and their resulting photophysical properties are explored. Upon excitation of the complexes at 490 nm, only LnIII emission is observed with efficiencies of 0.29 % at 976 nm for LnIII =YbIII and 0.16 % at 1053 nm for LnIII =NdIII . ErIII emission is observed but weak. Upon excitation at 400 nm, concurrent 1 O2 formation is seen, with efficiencies of 11 % for the YbIII and NdIII complexes and 13 % for the ErIII complex. Owing to the concurrent generation of 1 O2 , as expected, the efficiency of metal-centered emission decreases to 0.02 % for YbIII and 0.05 % for NdIII . The ability to control 1 O2 generation through the excitation wavelength indicates that the incorporation of 2,2':5',2''-terthiophene results in access to multiple sensitization pathways. These energy pathways are unraveled through transient absorption spectroscopy.

Recognition of antioxidants and photosensitizers in Dyssodia pinnata by EPR spectroscopy.

INTRODUCTION: Previous studies report the isolation mainly of terthiophene derivatives and flavonoids from Dyssodia species. Terthiophenes are known as photosensitizers by their capacity to generate singlet oxygen (1 O2 ), and flavonoid antioxidant activity is recognized. These opposite properties could represent interesting options in photodynamic therapy. OBJECTIVE: To determine the antioxidant and photosensitizer activities of extracts and isolates of Dyssodia pinnata by electron paramagnetic resonance (EPR). METHODOLOGY: Extracts and isolates were evaluated as antioxidants by the interactions with copper ion (Cu2+ ) observed in EPR, and by the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and the thiobarbituric reactive substances (TBARS) methods. Their abilities as 1 O2 producers were also estimated by EPR. RESULTS: Terthiophenes were obtained from hexane (DPH) and acetone (DPA) extracts, and flavonoids from DPA and methanol (DPM) extracts. The interaction with Cu2+ of extracts and isolated compounds of Dyssodia pinnata showed two effects in EPR: reduction and chelation; flavonoids exhibited both effects, while terthiophenes showed only reduction. DPA, DPM, and flavonoids were active in DPPH and TBARS assays. Quercetagetin-7-O-ß-glucoside showed the highest antioxidant and chelating activities, 3-glycosidated flavonoids were less active. Upon irradiation extracts and terthiophenes induced 1 O2 formation. CONCLUSION: Flavonoid reducing activity on Cu2+ and free radical scavenging capacity were related to the number of hydroxy groups and to the conjugation between the B and C rings. All tested flavonols showed a major complex with Cu2+ , with the most probable site of chelation between the 5-hydroxy and 4-oxo groups. Extracts and terthiophene derivatives showed photosensitizer activity. Thus, EPR is useful to evaluate free radical scavenging and pro-oxidant properties.

Synthesis and Cyclization-Induced Charge Transfer of Rectangular Bisterthiophenesiloxanes.

Cyclization-modified terthiophene displays the change of emission behavior from locally excited (LE) to the intramolecular charge transfer (ICT) state. The rectangular bisterthiophenesiloxanes (DSiTh) was successfully prepared by π-π-stacking-aided hydrogen-bonding interactions. Cyclization-induced ICT in DSiTh could be observed, which was confirmed by absorption spectra, fluorescence spectra, and quantum chemistry analysis. The cyclization produces a strong intramolecular electron redistribution of a highly packed π-conjugated terthiophene. Thus, a distinctive variation of the dipole moment and a through-space ICT happen.

A Carbonylated Terthiophene-Based Twisted Polymer for Efficient Ternary Polymer Solar Cells.

In polymer solar cells (PSCs), it is difficult for twisted conjugated polymers to achieve high power-conversion efficiency (PCE) as donors due to their low charge carrier mobilities and poor bulk heterojunction morphologies. In this work, a new twisted conjugated polymer (P3TCO-1) with excellent solubilities (above 30 mg mL-1 ) in common organic solvents at room temperature is reported. UV-visible absorption spectra and cyclic voltammetry indicate that P3TCO-1 has a wide optical bandgap of 1.90 eV and deep HOMO level of -5.39 eV. In binary PSCs, P3TCO-1:ITIC-based device shows a PCE of 10.11%, with JSC of 17.05 mA cm-2 and FF of 62.89%; P3TCO-1:PC71 BM-based device gives a PCE of 6.67% with JSC of 12.31 mA cm-2 and FF of 58.00%. When the two acceptors of ITIC and PC71 BM are combined, the twisted P3TCO-1-based ternary PSCs exhibit a significantly boosted PCE of up to 11.41%, with a simultaneously improved JSC of 18.16 mA cm-2 and FF of 66.78%. These results can guide the improvement of PCE for twisted conjugated polymer-based PSCs.

Comparison of a carboxylated terthiophene surface with carboxymethylated dextran layer for surface plasmon resonance detection of progesterone.

Functionalization of a gold surface is usually accomplished by covalent binding via self-assembled monolayers (SAMs) on the gold surface, followed by attachment of flexible polymeric linker layers such as dextran hydrogels. However, these techniques require multiple steps and also have nonspecific interactions and steric problems. In this study, a self-assembled carboxylated terthiophene monolayer was formed onto a gold surface to create a sensitive and stable surface plasmon resonance (SPR) biosensing system. Compared with a commercial carboxymethyl dextran chip (CM5), the terthiophene SAM surface provided more than six times more antibody-binding signals and nearly three times the SPR assay sensitivity for progesterone (P4).

Solar Cell Enhancement from Supercritical CO2 Dye Surface Modification of Mesoporous TiO2 Photoanodes.

In recent years, in an effort to reach Net Zero Emissions, there has been growing interest by various academic and industry communities to develop chemicals and industrial processes that are circular, sustainable and green. We report the rapid, simple and effective surface modification of a porous metal oxide with organic dyes using supercritical carbon dioxide (scCO2). Titanium dioxide (TiO2) photoanodes were coated in very short times, under mild conditions and the excess dye recovered afterwards for reuse. The process obviates the need for conventional toxic solvents, the generation of unwanted waste streams, and more importantly, we see an unexpected device performance enhancement of 212 and 163 % for TerCOOTMS, 2 a and TerCN/COOTBDMS, 4 dyes, respectively, when compared to the conventional solvent deposition method.

Vapor-Phase Formation of a Hole-Transporting Thiophene Polymer Layer for Evaporated Perovskite Solar Cells.

Homogeneous layer formation on textured silicon substrates is essential for the fabrication of highly efficient monolithic perovskite silicon tandem solar cells. From all well-known techniques for the fabrication of perovskite solar cells (PSCs), the evaporation method offers the highest degree of freedom for layer-by-layer deposition independent of the substrate's roughness or texturing. Hole-transporting polymers with high hole mobility and structural stability have been used as effective hole-transporting materials (HTMs) of PSCs. However, the strong intermolecular interactions of the polymers do not allow for a layer formation via the evaporation method, which is a big challenge for the perovskite community. Herein, we first applied a hole-transporting terthiophene polymer (PTTh) as an HTM for evaporated PSCs via an in situ vapor-phase polymerization using iodine (I2) as a sublimable oxidative agent. PTTh showed high hole mobility of 1.2 × 10-3 cm2/(V s) and appropriate energy levels as HTM in PSCs (EHOMO = -5.3 eV and ELUMO = -3.3 eV). The PSCs with the in situ vapor-phase polymerized PTTh hole-transporting layer and a co-evaporated perovskite layer exhibited a photovoltaic conversion efficiency of 5.9%, as a proof of concept, and high cell stability over time. Additionally, the polymer layer could fully cover the pyramidal structure of textured silicon substrates and was identified as an effective hole-transporting material for perovskite silicon tandem solar cells by optical simulation.

Novel Two-Dimensional Conjugated Polymer Containing Fluorinated Bithiophene as Donor and Benzoselenodiazole as Acceptor Units with Vinyl-Terthiophene Pendants for Polymer Photovoltaic Cells.

Novel two-dimensional conjugated copolymer, abbreviated as PDTBSeVTT-2TF, containing electron-deficient 4,7-di(thiophen-2-yl)benzo[c][1,2,5]selenodiazole (DTBSe) unit, conjugated vinyl-terthiophene (VTT) side chain and 3,3'-difluoro-2,2'-bithiophene (2TF) was designed and synthesized using microwave-assisted Stille cross-coupling polymerization. UV⁻visible absorption and cyclic voltammetry studies revealed that this copolymer possesses a strong and broad absorption in the range of 300⁻800 nm and a narrow optical bandgap (Eg) of 1.57 eV with low-lying HOMO and LUMO energy levels. Further, the bulk heterojunction polymer solar cells (PSCs) were fabricated using PDTBSeVTT-2TF as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor with an inverted device structure of ITO/ZnO/PDTBSeVTT-2TF:PC71BM/V2O5/Ag. The processing temperature of blend solution for preparing PDTBSeVTT-2TF:PC71BM active layer showed obvious impact on the photovoltaic performance of solar devices. The cell fabricated from the blend solution at 65 °C exhibited enhanced power conversion efficiencies (PCE) of 5.11% with a Jsc of 10.99 mA/cm-2 compared with the one at 50 °C, which had a PCE of 4.69% with a Jsc of 10.10 mA/cm-2. This enhancement is due to the dissolution of PDTBSeVTT-2TF clusters into single molecules and small aggregates, improving the miscibility between the polymer and PC71BM and thus increasing the donor/acceptor interface.

New Terthiophene-Conjugated Porphyrin Donors for Highly Efficient Organic Solar Cells.

To mimic the natural photosynthetic systems utilizing chlorophylls to absorb light and store light energy, two new porphyrin-based small molecules of PTTR and PTTCNR have been developed for photovoltaic applications. The highest power conversion efficiency of 8.21% is achieved, corresponding to a short-circuit current of 14.30 mA cm-2, open-circuit voltage of 0.82 V, and fill factor of 70.01%. The excellent device performances can be ascribed to the engineering of molecule structure and film morphology. The horizontal conjugation of 3,3″-dihexyl-terthiophene to porphyrin-core with the vertical aliphatic 2-octylundecyl peripheral substitutions, can not only effectively increase the solar flux coverage between the conventional Soret and Q bands of porphyrin unit, but also optimize molecular packing through polymorphism associated with side-chains and the linear π-conjugated backbones. And the additive of 1,8-diiodooctane and subsequent chloroform solvent vapor annealing facilitate the formation of the blend films with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) characteristics of bicontinuous, interpenetrating networks required for efficient charge separation and transportation.

Constituents of the aerial parts of Eclipta prostrata and their cytotoxicity on human ovarian cancer cells in vitro.

A new terthiophene, 3'-hydroxy-2,2':5',2″-terthiophene-3'-O-ß-D-glucopyranoside (1) and a new oleanane-type saponin, echinocystic acid-3-O-(6-O-acetyl)-ß-D-glucopyranoside (7) were isolated from the aerial parts of Eclipta prostrata L. Moreover, five thiophenes (2-6), seven triterpenoids (8-14), two coumestans (15 and 16), and four flavonoids (17-20) having previously known chemical structures were isolated during the same course of this study. All the isolates 1-20 were evaluated for their cytotoxicity against human ovarian cancer cells (SKOV3) using MTT assays.

Terthiophene-containing copolymers and homopolymer blends as high-performance dielectric materials.

This work explores the dielectric and polarization properties of block copolymers and homopolymer blends containing a terthiophene-rich, electronically polarized block (PTTEMA) and an insulating polystyrene block (PS). PTTEMA-b-PS block copolymers were synthesized by reverse addition-fragmentation chain transfer (RAFT) polymerization, and PTTEMA/PS homopolymer blends with the same PTTEMA weight percentages were produced by solution blending. DSC and XRD characterization show that crystallinity increases with PTTEMA content, indicating the presence of terthiophene-rich crystalline domains. Under an applied electric field, these domains are electronically polarized, but the insulating PS block inhibits current leakage, resulting in enhanced dielectric properties. Impedance measurements show that relative permittivity increases with PTTEMA content. The permittivity values are higher in PTTEMA-b-PS copolymers with moderate PTTEMA content due to the ability of the PS block to inhibit PTTEMA association, resulting in a higher density of isolated, terthiophene-rich polarizable domains. Freestanding PTTEMA/PS blend films containing up to 40 wt % PTTEMA have almost 40% greater recoverable energy density compared to pure PS films polarized to the same electric field strength.

Terthiophene on Au(111): A scanning tunneling microscopy and spectroscopy study.

Terthiophene (3T) molecules adsorbed on herringbone (HB) reconstructed Au(111) surfaces in the low coverage regime were investigated by means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) under ultra-high vacuum conditions. The 3T molecules adsorb preferentially in fcc regions of the HB reconstruction with their longer axis oriented perpendicular to the soliton walls of the HB and at maximum mutual separation. The latter observation points to a repulsive interaction between molecules probably due to parallel electrical dipoles formed during adsorption. Constant-separation (I-V) and constant-current (z-V) STS clearly reveal the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals, which are found at -1.2 eV and +2.3 eV, respectively. The HOMO-LUMO gap corresponds to that of a free molecule, indicating a rather weak interaction between 3T and Au(111). According to conductivity maps, the HOMO and LUMO are inhomogeneously distributed over the adsorbed 3T, with the HOMO being located at the ends of the linear molecule, and the LUMO symmetrically with respect to the longer axis of the molecule at the center of its flanks. Analysis of spectroscopic data reveals details of the contrast mechanism of 3T/Au(111) in STM. For that, the Shockley-like surface state of Au(111) plays an essential role and appears shifted outwards from the surface in the presence of the molecule. As a consequence, the molecule can be imaged even at a tunneling bias within its HOMO-LUMO gap. A more quantitative analysis of this detail resolves a previous discrepancy between the fairly small apparent STM height of 3T molecules (1.4-2.0 nm, depending on tunneling bias) and a corresponding larger value of 3.5 nm based on X-ray standing wave analysis. An additionally observed linear decrease of the differential tunneling barrier at positive bias when determined on top of a 3T molecule is compared to the bias independent barrier obtained on bare Au(111) surfaces. This striking difference of the barrier behavior with and without adsorbed molecules is interpreted as indicating an adsorption-induced dimensionality transition of the involved tunneling processes.