Thiophene Chromophores Research Articles

A first principles based prediction of electronic and nonlinear optical properties towards cyclopenta thiophene chromophores with benzothiophene acceptor moieties

In the current work, organic cyclopenta-thiophene (CPT) based derivatives (FICR and FICD1–FICD5) were designed by the modulation of end-capped acceptor group of the reference molecule i.e., FICR, to explore their nonlinear optical (NLO) response. The effect of terminal acceptor and donor groups in the tailored compounds was explored by using DFT based quantum calculations. The UV–Vis analysis, frontier molecular orbitals (FMOs), transition density matrix (TDM), natural bond orbitals (NBOs), density of states (DOS), nonlinear optical (NLO) analyses were performed at M06/6-311G(d,p) functional. The LUMO–HOMO band gaps of FICD1–FICD5 were found to be smaller (1.75–1.92 eV) comparative to FICR (1.98 eV). Moreover, the global reactivity parameters (GRPs) were correlated with the results of other analyses. FICD2 and FICD5 with lowest band gap 1.73 and 1.75 eV showed less hardness (0.86 and 0.87 eV, respectively), high softness (0.58 and 0.57 eV−1), and larger absorption spectrum (815 and 813 nm) in gaseous phase and (889 and 880 nm) in solvent phase among all entitled compounds. All the designed chromophores (FICD1–FICD5) demonstrated a significant NLO response as compared to FICR. Particularly, FICD2 and FICD5 exhibited the highest average linear polarizability (<α>) [2.86 × 10−22 and 2.88 × 10−22 esu], first hyperpolarizability (βtot) (8.43 × 10−27 and 8.35 × 10−27 esu) and second hyperpolarizability (γtot) (13.20 × 10−32 and 13.0 × 10−32 esu) values as compared to the other derivatives. In nutshell, structural modeling of CPT based chromophores with extended acceptors, can be significantly utilized to achieve potential NLO materials.

Core effect on indacenodithieno[3,2-b]thiophene dimer based small molecule acceptors for non-fullerene polymer solar cells

Dimerization is a widely adopted approach to construct electron accepting materials for polymer solar cells (PSCs). Fullerene dimers were extensively explored with improved structural stability and perylene-diimide (PDI) dimers prevented the formation of undesired large crystals. However, dimers of indacenodithieno[3,2-b]thiophene (IDTT) chromophores have yet not been reported despite the great success in non-fullerene small molecule acceptors (NF-SMAs) such as ITIC. In this work, we designed and synthesized three IDTT dimers with conjugated cores or not and explored the core effect of introducing flexible dithiophene or rigid thienothiophene as linkage group. All the three IDTT dimers were found to be poorly crystallized and functional PSCs devices containing each of these dimers were successfully fabricated paring with donor polymer PBDB-T. The introduction of electron donating linkages raise energy levels of the dimers hence increased the open circuit voltages. Thienothiophene was found to be a more suitable linkage unit than dithiophene but the highest power conversion efficiency of 6.01% was recorded in devices based on dimer dIDTT without the linkage units. This work demonstrated the possibility of using IDTT chromophore to construct dimer NF-SMAs and revealed insights of core effect on their photovoltaic performance.

Push-pull thiophene chromophores for electro-optic applications: from 1D linear to β-branched structures.

We report the synthesis and characterization of a novel series of push-pull chromophores bearing 1D linear and β-branched thiophenes as π-conjugated spacers between a 2,2,4,7-tetramethyl-1,2,3,4-tetrahydroquinoline electron donor unit and dicyano- and tricyanovinylene electron acceptor groups. The effect of the introduction of β-thiophenes on the linear and nonlinear (NLO) optical properties as well as electrochemical and thermal data is studied in detail by performing a comparative study between the branched and 1D linear systems. In addition, a parallel DFT computational study is used to evaluate structure-property relationships. The non-linear optical behavior of the molecules both in solution and in solid state as electro-optic (EO) films using a guest-host approach shows very promising performance for electro-optic applications with high molecular first hyperpolarizabilities (μβ) of 4840 × 10-48 esu and electro-optic coefficients r33 reaching 650 pm V-1. One highlight is that the electro-optic films of the β-branched chromophores are superior in terms of thermal stability in device operation as measured by a transmissive modified reflective Teng-Man method. This work provides guidelines for the design of improved electro-optic materials including β-branched chromophores which could be useful for practical EO applications, where both enhanced β and r33 values together with chemical and thermal stability are necessary.

Effect of the second chromophore energy gap on photo-induced electron injection in di-chromophoric porphyrin-sensitized solar cells.

This work investigates the effect of the second chromophore energy gap on charge generation in porphyrin-based di-chromophoric dye-sensitized solar cells (DSSCs). Three di-chromophoric porphyrin dyes (PorY, PorO and PorR) containing three organic chromophores with decreasing frontier orbital energy offsets, including a carbazole-triphenylamine chromophore (yellow, Y), a carbazole fused-thiophene chromophore (orange, O) or a carbazole-thiophene benzothiadiazole thiophene chromophore (red, R), were investigated using optical and electrochemical methods, steady-state photoluminescence and photovoltaic device characterization. Energy transfer from the organic chromophore to the porphyrin was suggested in PorY and PorO as the main charge generation mechanism in DSSCs using these di-chromophoric dyes. On the other hand, electron transfer from the photo-excited porphyrin to the organic chromophore as a competing pathway leading to the loss of photocurrent is suggested for PorR-sensitized solar cells. The latter pathway leading to a loss of photocurrent is due to the lower lying lowest unoccupied molecular orbital of the additional organic chromophore (R) and suggests the limitation of the current di-chromophoric approach to increase the overall efficiency of DSSCs.

Electro-optic properties of a side chain poly(norbornene-dicarboximide) system with an appended phenyl vinylene thiophene chromophore

A side chain EO copolymer series has been synthesized by ROMP using the Grubbs 3rd generation initiator and quenched with ethyl vinyl ether. The copolymers were prepared by combining two norbornene-dicarboximide monomers, one with a cyclohexyl substituent and another substituted with an FTC chromophore. The mol% of the chromophore-substituted monomer was varied from 0.00 mol% to 22.92 mol%, all polymers were obtained in a yield of between 83 and 92% and a purity of between 97 and 98%. The cis:trans vinylene ratio remained constant at 1:1, confirming the polymers were amorphous. Peak molecular weights increased from 29,541 g/mol to 142,113 g/mol and the PDI increased from 1.36 to 4.01 respectively. Glass transition and thermal decomposition temperatures decreased from 206 °C to 168 °C and 433 °C to 382 °C as the mol% of the chromophore-substituted monomer was increased. UV–vis absorbance spectroscopy was used to quantify the chromophore content. A close correlation (68–95%) between the measured and calculated absorbance was found. The polymer containing 22.92 mol% of the chromophore-substituted monomer had a maximum r33 of 70 pm/V when polled at an optimum field of 60 V/μm at a polling temperature of 200 °C. This equates to a high polling efficiency of 1.16. High current flow in this polymer film at elevated field strength caused a breakdown of the electrode, preventing access to an elevated electro-optic coefficient. This polymer was found to have an excellent stability of 76% when aged at 85 °C for 1000 h in air.

Synthesis and fluorescence emission properties of D-π-D monomers based on dithieno[3,2-b:2′,3′-d]thiophene

We herein present four highly fluorescent and stable D-π-D monomers (2), which were designed and synthesized using different types of aryl substituent as the donor via a Suzuki-Miyaura coupling reaction. We have studied these four symmetrical chromophores by UV–vis absorption and fluorescence emission spectroscopy both in solution and the solid state. This research shows that the introduction of the aryl groups can effectively reduced the HOMO-LUMO gap of thiophene chromophore resulting in a shift of the wavelength of the absorption and fluorescence emission. The notable optical features of their solid-state powders also exhibited a distinct red-shift in comparison with the emissions of their dilute solutions. These results combined with the theoretical calculations (B3LYP/6–31G*) indicate that these systems are promising candidates in the fabrication of organic electroluminescence devices.

Zinc(II) complexes of carboxamide derivatives: Crystal structures and interaction with calf thymus DNA

Two mononuclear zinc(II) complexes of newly designed carboxamide derivatives, formulated as [Zn(L1)3](ClO4)2 (1) and [Zn(L2)3](ClO4)2 (2) [where L 1 = N-(furan-2-ylmethyl)-2-pyridinecarboxamide and L 2 = N-(thiophen-2-ylmethyl)-2-pyridine-carboxamide], have been isolated in pure form in the reaction of perchlorate salts of Zn(II) with ligands L 1 and L 2 , respectively. The two complexes were characterized by physicochemical and spectroscopic tools, and by X-ray crystal structures of both ligands and the complex 1. In complex 1, zinc(II) is chelated by three ligands with a distorted octahedral geometry. The DNA-binding properties of zinc complexes 1 and 2 have been investigated by spectroscopic methods and viscosity measurements. The results suggest that both complexes 1 and 2 bind to DNA in an intercalation mode between the uncoordinated furan or thiophene chromophore and the base pairs of DNA.

Synthesis, crystal structure, redox behavior and DNA-binding properties of a series of copper(II) complexes with two new carboxamide derivatives

Four mononuclear copper(II) complexes of two new carboxamide derivatives formulated as [Cu(L1)2](ClO4)2 (1a), [Cu(L1)2](NO3)2 (1b), [Cu(L2)2(H2O)2](ClO4)2 (2a), and [Cu(L2)2(H2O)](NO3)2 (2b) have been isolated in pure form from the reaction of L1 and L2 [where L1 = N-(furan-2-ylmethyl)-2-pyridinecarboxamide and L2 = N-(thiophen-2-ylmethyl)-2-pyridinecarboxamide] with copper(II) salts of perchlorate and nitrate. All the complexes were characterized by physicochemical and spectroscopic tools along with single-crystal X-ray diffraction studies. The structural analyses showed that 1 is monomeric of square planar geometry with copper(II) chelated by two L1 ligands. Complex 2 differs in coordination geometry, being octahedral and distorted square pyramidal. Two L2 ligands occupy the equatorial positions of the octahedral 2a and the basal sites of the pyramidal 2b, with water molecules that complete the coordination sphere in each case. Electrochemical studies using cyclic voltammetry showed a reversible redox behavior of the copper(II) in 1 and 2. The electronic spectroscopic behavior and the trend of one electron equivalent redox potential corresponding to a CuII/CuI couple have also been confirmed by density functional theory calculations. The spectroscopic and viscosity measurement study in tris–HCl buffer suggested an intercalative interaction of 1a and 2 with calf thymus DNA likely due to the stacking between the non-coordinated furan and thiophene chromophore with the base pairs of DNA.

Charge Generation, Regeneration and Recombination in Di-Chromophoric Carbazole-Thiophene-Porphyrin-Sensitised Solar Cells

Porphyrins are among the best performing dyes for their application in dye-sensitized solar cells. However, light harvesting efficiencies between the Soret and Q bands of most simple porphyrins are limited, especially when thin electrodes or electrodes with low surface area are used. Filling the absorption gap is an important objective to further enhance their efficiency, in addition to extending their absorption band edge to better match the solar spectrum. In this work, the absorption gap between the Soret and Q bands is filled using a multi-chromophoric approach following the synthetic strategy we have developed earlier (J. Am. Chem. Soc. 2009, 131, 15621-15623; J. Mater. Chem. A 2014, 2, 16963-16977). Three new porphyrin dyes with carbazole-fused thiophene chromophores attached to the porphyrin core using a non-conjugated phenylethenyl linker are synthesised. When attached to TiO2, an almost complete filling of the absorption gap within the 450 nm to 500 nm is achieved, which leads to doubling of the short circuit current density using the Co2+ / Co3+ electrolyte. In addition, the electron lifetime has significantly improved contributing to increased power conversion efficiency of 4.7%. Particularly significant result is the nearly 100% absorbed photon to collected electron efficiency at wavelengths dominated by the side chain absorption, suggesting the promise of the multi-chromophoric dye design using the non-conjugated approach. Detailed transient absorption and spectro-electrochemical investigations reveal a significant acceleration of dye cation regeneration kinetics in carbazole-porphyrin dyads attached to TiO2. This is attributed to a picosecond to microsecond intramolecular hole transfer from the porphyrin cation to carbazole, followed by a fast reduction of the carbazole cation by the electron donor redox mediator dissolved in the electrolyte. Such increase of the turnover rates without affecting the final electrochemical potential of the photo-generated species is promising for a variety of photo-electrochemical energy conversion processes, including solar cells and solar fuels.

Graphene-Based Hybrid Materials Incorporating Multichromophores

Hybrid materials based on graphene have the potential to drive a variety of nanotechnological applications ranging from optoelectronics, to biomedical, as well as, industrial. Herein, we present an array of novel graphene-based materials incorporating one or more chromophore systems, anchored onto graphene through covalent or non-covalent interactions, targeted for energy conversion schemes.Graphene single- and/or few-layered graphene sheets have been prepared through ultrasonication processes, introducing minimal defects onto the graphitic backbone while affording comparatively large quantities to allow for chemical modification.1 The chromophores selected to form hybrid graphene nanoensembles, through covalent bond formation, range from pyrene, porphyrin and oligo-thiophene adducts.2 The resulting hybrids afforded stable suspensions in a variety of common organic solvents and allowed for detailed characterization in liquid phase. In addition, non-covalently formed graphene-based nanoensembles were also prepared and the various systems comprised of thiophene chromophores, but also pyrene-porphyrin and dual porphyrin systems.2 All synthesized hybrids have been extensively characterized with thermogravimetric analysis, microRAMAN, and optical techniques (absorption, steady state and time-resolved photoluminescence spectroscopy) among others to verify, the structural and optoelectronic properties of the nanoensembles. Also due to the increased solubility of the hybrids and the ability to form stable suspensions, electrochemistry was used to elucidate the energy levels of the chromophores, as well as the resulting hybrids, affording insight on the thermodynamically favored mechanisms in the system. Finally, time-resolved photoluminescence experiments verify the promotion of electronic communication of the chromophores with the graphene substrate.Financial support from GSRT/NSRF 2007-2013 through action “Supporting Postdoctoral Researchers” project GRAPHCELL PE5(2126) is acknowledged.ReferencesS. P. Economopoulos, N. Tagmatarchis, Chem. Eur. J. 2013, 19, 12930.S. P. Economopoulos, N. Tagmatarchis, Manuscript in preparation, 2014.

Benzo[ c ]thiophene Chromophores Linked to Cationic Fe and Ru Derivatives for NLO Materials: Synthesis Characterization and Quadratic Hyperpolarizabilities

η5-Monocyclopentadienyliron(II)/ruthenium(II) complexes of the general formula [M(η5-C5H5)(PP)(L1)][PF6] {M = Fe, PP = dppe; M = Ru, PP = dppe or 2PPh3; L1 = 5-[3-(thiophen-2-yl)benzo[c]thiophenyl]thiophene-2-carbonitrile} have been synthesized and studied to evaluate their molecular quadratic hyperpolarizabilities. The compounds were fully characterized by NMR, FTIR and UV/Vis spectroscopy and their electrochemical behaviour studied by cyclic voltammetry. Quadratic hyperpolarizabilities (β) were determined by hyper-Rayleigh scattering measurements at a fundamental wavelength of 1500 nm. Density functional theory calculations were employed to rationalize the second-order non-linear optical properties of these complexes.

Fluorescence and two-photon absorption of push—pull aryl(bi)thiophenes: structure—property relationships

Photophysical and TPA properties of series of push-pull aryl(bi)thiophene chromophores bearing electron-donating (D) and electron-withdrawing (A) end-groups of increasing strength are presented. All compounds show an intense intramolecular charge transfer (ICT) absorption band in the visible region. Increasing the D and/or A strength as well as the length of the conjugated path induces bathochromic and hyperchromic shifts of the absorption band as reported for analogous push-pull polyenes. Yet, in contrast with corresponding push-pull polyenes, a significant increase in fluorescence is observed. In particular, chromophores built from a phenyl-bithienyl conjugated path and bearing strong D and A end-groups were found to combine very large one and two-photon brightness as well as strong emission in the red/NIR region. These molecules hold promise as biphotonic fluorescent probes for bioimaging.

Synthesis and optoelectronic properties of luminescent copolyfluorenes slightly doped with thiophene chromophore

This paper describes the synthesis of new copolyfluorenes ( P05– P5) slightly doped with 2,5-bis(2-phenyl-2-cyanovinyl)thiophene ( GM, <3.4 mol%) and their application in electroluminescent (EL) devices. In film state, EL spectra of the copolyfluorenes are very different from photoluminescence (PL) spectra, which have been ascribed to charge trapping in GM and energy transfer from fluorene segments to GM chromophores. The maximum brightness and current efficiency of EL device from P05 (5230 cd/m 2, 0.65 cd/A) are significantly enhanced when compared with those from poly(9,9-dihexylfluorene) ( PF) (1310 cd/m 2, 0.18 cd/A). The EL device using blend of P5 and PF ( w/ w = 10/1) as emitting layer exhibits near-white emission with CIE coordinate being (0.26, 0.32). The results demonstrate that the copolyfluorenes slightly doped with GM chromophore are promising emitting materials for optoelectronic devices.

Synthesis and NLO properties of hybrid inorganic–organic films containing thiophene ring

A family of second-order nonlinear optical sol–gel films with a pendent thiophene chromophore has been developed. The key step in preparation these hybrids was the syntheses of alkoxysilane dye containing thiophene ring, which was accomplished by utilizing the urethane forming reaction. Molecular structural characterization for the resultant was achieved by FTIR, 1H NMR and UV–Visible spectra. The microscopic optical nonlinearity of the thiophene chromophore was evaluated to be 7646 × 10 − 30 esu D by solvatochromic method and second harmonic coefficients ( d 33) of the hybrid film was also calculated to be 41.2 pm/V by second harmonic generation (SHG) measurements, respectively. Furthermore, the stability of optical nonlinearity in poled film was also investigated through a depoling experiment.

The synthesis and electron structure of oligothiophenes terminated with (10H-anthracen-9-one) methylene chromophores

The synthesis, spectral measurements and theoretical study of simple model oligothiophenes terminated symmetrically or asymmetrically by (10H-anthracen-9-one) methylene chromophore are presented. The electron absorption spectra of these novel molecules were measured in polymer matrices and chloroform solution. The absorption spectra of investigated systems measured in chloroform are characterised by a broad low energy band with partially distinguished vibrational structure. Theoretical calculations of electronic ground state structures have been performed at the density functional theory (DFT) level of the theory. The vertical excitations energies were calculated using the time-dependent version of DFT (TD-DFT) and semiempirical Zerner's Intermediate Neglect of Differential Overlap methods. The role of the termination group upon the vertical excitation was estimated from the localisation of highest and lowest occupied orbitals. This analysis showed that the excitation energy transfer upon the optical excitation leads from the thiophene chromophores into the central part of (10H-anthracen-9-one) methylene unit.

Copolyfluorenes containing phenothiazine or thiophene derivatives: Synthesis, characterization, and application in white‐light‐emitting diodes

AbstractFour copolyfluorenes chemically doped with 0.1 and 1 mol % 3,7‐bis[2‐thiophene‐2‐yl)‐2‐cyanovinyl]phenothiazine (PFPhT) or 2,5‐bis[2‐(thiophene‐2‐yl)‐2‐cyanovinyl]thiophene chromophores (PFThT) were synthesized using the Suzuki coupling reaction and applied in white‐light‐emitting devices. They were characterized by GPC, elemental analysis, DSC, TGA, optical spectra, and cyclic voltammetry. They exhibited good thermal stability (Td &gt; 420 °C) and moderate glass transition temperatures (&gt;95 °C). The PhT‐Br and ThT‐Br showed PL peaks at 586 and 522 nm (with a shoulder at 550 nm). In film state, PL spectra of the copolymers comprised emissions from the fluorene segments and the chromophores due to incomplete energy transfer. Both monomers exhibited low LUMO levels around −3.50 to −3.59 eV, whereas the PhT‐Br owned the higher HOMO level (−5.16 eV) due to its electron‐donating phenothiazine core. Light‐emitting diodes with a structure of ITO/PEDOT:PSS/copolymer/Ca(50 nm)/Al(100 nm) showed broad emission depending on the chromophore contents. The maximum brightness and maximum current efficiency of PFPhT2 (PFThT1) device were 8690 cd/m2 and 1.43 cd/A (7060 cd/m2 and 0.98 cd/A), respectively. White‐light emission was realized by further blending PFPhT2 with poly(9,9‐dihexylfluorene) (w/w = 10/1), with the maximum brightness and maximum current efficiency being 10,600 cd/m2 and 1.85 cd/A. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 833–844, 2009

Interactions Between Gold Nanoparticles and Polymer Bearing 3-Styryl Thiophene Chromophores

The interactions between gold nanoparticles and a novel acrylate copolymer bearing 3-styryl thiophene chromophores were studied spectrally and electrochemically. The emission intensity of the polymer solution can be quenched by gold nanoparticles. Collisional quenching is likely the main mechanism for the deactivation process and heterogeneous electron transfer takes place in the process. For the solid polymer film, the presence of gold nanoparticles reduces the emission intensity of the single chromophore as well as the intensity of the excimers. Cyclic voltammetry (CV) investigations indicate that the polymer solution exhibits no oxidation wave. However, in the presence of gold nanoparticles, either by directly addition to the polymer solution or by deposition on the ITO electrode, the polymer solutions possess distinct CV oxidation peak(s), indicating that the gold nanoparticles may mediate the contact and enhance the electron transfer between the electrode and chromophores.

NMR studies of the reaction between amino-phenylene vinylene thiophene and tetracyanoethylene

Amino tricyanovinyl thiophene chromophores (A-TCVT) are prepared by a substitution reaction of amino-phenylene vinylene thiophene (A-PVT) with tetracyanoethylene (TCNE). This reaction does not occur directly. The vinylene double bond in the PVT unit first reacts rapidly with TCNE to form a [2+2] cycloaddition product. It is then reverted to PVT unit prior to the subsequent substitution at 50 °C. This reversible cycloaddition converts the cis-isomer of PVT units into the trans-counterparts, thus the final TCNE substituted products can be expected for a better performance as non-linear optical materials.

Structure, electronic and optical characterization of oligothiophenes terminated with (9H-fluoren-9-ylidene)methyl chromophores

The synthesis, spectral measurements and theoretical study of oligothiophenes terminated by (9H-fluoren-9-ylidene)methyl chromophores at the one (series A N ) and both (series B N ) ends are presented. The electron absorption and fluorescence spectra of prepared molecules were measured in polymer matrices and chloroform solution. The absorption and fluorescence spectra of the investigated systems are represented by broad band without vibrational structure. Well detectable fluorescence is observed for the compounds of the B N family. The experimentally observed medium large Stokes shifts (less than 5000 cm −1) indicate restricted geometrical changes in molecular chain upon optical excitation. Experimental lifetimes of fluorescence are shorter than 1 ns. Theoretical calculations have been performed at the semiempirical Austin Model 1 (AM1) and density functional theory (DFT) levels of the theory. The planarisation of dihedral angles between the fluorene and thiophene chromophores upon optical excitation theoretically was characterised, as well.

Donor–acceptor molecules containing thiophene chromophore: synthesis, spectroscopic study and electrogenerated chemiluminescence

Donor–acceptor molecules containing thiophene chromophore with remarkably large Stokes shift (>210 nm) have been found to exhibit strong and stable ECL emission via the singlet excited state without the addition of any co-reactant or a second compound.