Thienyl Units Research Articles

Hypoxia-Active Iridium(III) Bis-terpyridine Complexes Bearing Oligothienyl Substituents: Synthesis, Photophysics, and Phototoxicity toward Cancer Cells.

In an effort to develop hypoxia-active iridium(III) complexes with long visible-light absorption, we synthesized and characterized five bis(terpyridine) Ir(III) complexes bearing oligothienyl substituents on one of the terpyridine ligands, i.e., nT-Ir (n = 0-4). The UV-vis absorption, emission, and transient absorption spectroscopy were employed to characterize the singlet and triplet excited states of these complexes and to explore the effects of varied number of thienyl units on the photophysical parameters of the complexes. In vitro photodynamic therapeutic activities of these complexes were assessed with respect to three melanoma cell lines (SKMEL28, A375, and B16F10) and two breast cancer cell lines (MDA-MB-231 and MCF-7) under normoxia (∼18.5% oxygen tension) and hypoxia (1% oxygen tension) upon broadband visible (400-700 nm), blue (453 nm), green (523 nm), and red (633 nm) light activation. It was revealed that the increased number of thienyl units bathochromically shifted the low-energy absorption bands to the green/orange spectral regions and the emission bands to the near-infrared (NIR) regions. The lowest triplet excited-state lifetimes and the singlet oxygen generation efficiency also increased from 0T to 2T substitution but decreased in 3T and 4T substitution. All complexes exhibited low dark cytotoxicity toward all cell lines, but 2T-Ir-4T-Ir manifested high photocytotoxicity for all cell lines upon visible, blue, and green light activation under normoxia, with 2T-Ir showing the strongest photocytotoxicity toward SKMEL28, MDA-MB-231, and MCF-7 cells, and 4T-Ir being the most photocytotoxic one for B16F10 and A375 cells. Singlet oxygen, superoxide anion radicals, and peroxynitrite anions were found to likely be involved in the photocytotoxicity exhibited by the complexes. 4T-Ir also showed strong photocytotoxicity upon red-light excitation toward all cell lines under normoxia and retained its photocytotoxicity under hypoxia toward all cell lines upon visible, blue, and green light excitation. The hypoxic activity of 4T-Ir along with its green to orange light absorption, NIR emission, and low dark cytotoxicity suggest its potential as a photosensitizer for photodynamic therapy applications.

Syntheses of Thiophene-Thiophene-Linked Corrorin Dimers with Tunable Near-Infrared Absorption and Distinctive Reactivity.

Thiahexaphyrinone 1 and thia-dipyrrin-appended corrorin 2 have been synthesized. Surprisingly, further oxidation of compound 2 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dichloromethane afforded dimer 3 with two molecules of compound 2 linked at the α-carbon atoms of the thienyl units. Treatment of compound 3 with DDQ in MeOH and SnCl2 in tetrahydrofuran/H2O afforded the dimethoxy-attached dimer 4 and hydrogenated dihydroxy-attached dimer 5, respectively. These results provide the first examples for synthesizing thiophene-linked porphyrinoid dimers with tunable near-infrared absorption and chirality.

Synthesis of novel phenothiazine, phenoxazine and carbazole derivatives via Suzuki-Miyaura reaction

The Suzuki-Miyaura cross-coupling reaction was utilized for the synthesis of 15 new compounds containing phenothiazine (PTZ), phenoxazine (POZ), carbazole (Cz), and triphenylamine (TPA) as good electron donors. The synthesized compounds were furnished with active carbaldehyde groups and decorated with phenyl, thienyl, furyl, imidazolyl, or oxadiazolyl units linked to either one or two sides of the central cores (PTZ, POZ, and Cz). A simple catalytic systems based on Pd(PPh3)4 were tried and the results showed better CC coupling efficiencies of the electron-rich phenothiazine halides over phenoxazine and carbazole analogues when coupled with either electron-rich or electron-deficient boronic acid precursors. Besides, the coupling process of substituted phenothiazine halides with different boronic acids precursors, based on phenyl (Ph), furyl (Fu) and thienyl (Th) units, was found to be dependent on the electronic nature of both PTZ-halide and boronic acid precursors. Coupling efficiency of Ph, Fu, and Th rings with the skeleton of imidazolyl-PTZ-Br coupler to bring up compounds 6a-c showed the order: Ph>Fu>Th (with the yield of 86, 85, and 80%, respectively), while coupling efficiency of the brominated PTZ-oxadiazolyl-phenyl coupler with different arylboronic acids showed the order of Th>Ph>Fu to obtain compounds 8a-c. Additionally, the TPA derivative 11b was obtained with an excellent yield of 96% using Pd(PPh3)4 . The successful activation of the synthesized derivatives with carbaldehyde groups and the integration of different spacers made them substantially suitable to be exploited as promising intermediates for the future synthesis of versatile π-conjugated systems.

Syntheses of thiophene appended N-confused phlorin isomers

A doubly confused thiapentapyrrane NSP-5 was synthesized by acid-catalysed condensation. Subsequent oxidation with DDQ did not afford the expected thiasapphyrin-like product. Instead, two tetrapyrrolic macrocycles, i.e. neo-N-confused phlorin (1) and N-confused phlorin-II (2) were obtained in the yields of 14% and 18%, respectively. The compounds were characterized by NMR, HRMS, and X-ray diffraction analyses. Single crystal structures clearly reveal that the thienyl units are not embedded into the macrocycles, but appended as meso-substituents, and the C[Formula: see text]-N and C[Formula: see text]-C[Formula: see text] cyclization modes can be clearly revealed by the crystal structures of 1 and 2, respectively. The observation that the thienyl unit is not involved in oxidative cyclization may be related to the relatively low reactivity of the thiophene moiety compared with the more electron-rich pyrrole unit. These results indicate that oxidative cyclization of linear thiaoligopyrranes containing terminal thiophene units may be developed as an effective approach for synthesizing nonconjugated macrocycles like phlorin analogues.

Synthesis of Amorphous Conjugated Copolymers Based on Dithienosilole-Benzothiadiazole Dicarboxylic Imide with Tuned Optical Band Gaps and High Thermal Stability

Two alternating copolymers of dithienosilole (DTS) were designed and synthesized with small optical band gaps, flanked by thienyl units as electron-donor moieties and benzothiadiazole dicarboxylic imide (BTDI) as electron-acceptor moieties. The BTDI moieties were anchored to two different solubilizing side chains, namely 3,7-dimethyloctyl and n-octyl chains. An analysis of the effect of the electrochemical, optical, thermal, and structural characteristics of the resulting polymers along with their solubility and molecular weight is the subject of this paper. The Stille polymerization was used to synthesize PDTSDTBTDI-DMO and PDTSDTBTDI-8. The average molecular weight of PDTSDTBTDI-DMO and PDTSDTBTDI-8 is 14,600 and 5700 g mol−1, respectively. Both polymers have shown equivalent optical band gaps around 1.4 eV. The highest occupied molecular orbital (HOMO) levels of the polymers were comparable, around −5.2 eV. The lowest unoccupied molecular orbital (LUMO) values were −3.56 and −3.45 eV for PDTSDTBTDI-DMO and PDTSDTBTDI-8, respectively. At decomposition temperatures above 350 °C, both copolymers showed strong thermal stability. The studies of powder X-ray diffraction (XRD) have shown that they are amorphous in a solid-state.

Optical, Electrochemical, Thermal, and Structural Properties of Synthesized Fluorene/Dibenzosilole-Benzothiadiazole Dicarboxylic Imide Alternating Organic Copolymers for Photovoltaic Applications

In this work, four donor–acceptor copolymers, PFDTBTDI-DMO, PFDTBTDI-8, PDBSDTBTDI-DMO, and PDBSDTBTDI-8, based on alternating 2,7-fluorene or 2,7-dibenzosilole flanked by thienyl units, as electron-donor moieties and benzothiadiazole dicarboxylic imide (BTDI) as electron-accepting units, have been designed and synthesized for photovoltaic applications. All polymers were synthesized in good yields via Suzuki polymerization. The impact of attaching two different alkyl chains (3,7-dimethyloctyl vs. n-octyl) to the BTDI units upon the solubilities, molecular weights, optical and electrochemical properties, and thermal and structural properties of the resulting polymers was investigated. PFDTBTDI-8 has the highest number average molecular weight (Mn = 24,900 g·mol−1) among all polymers prepared. Dibenzosilole-based polymers have slightly lower optical band gaps relative to their fluorene-based analogues. All polymers displayed deep-lying HOMO levels. Their HOMO energy levels are unaffected by the nature of either the alkyl substituents or the donor moieties. Similarly, the LUMO levels are almost identical for all polymers. All polymers exhibit excellent thermal stability with Td exceeding 350 °C. X-ray powder diffraction (XRD) studies have shown that all polymers have an amorphous nature in the solid state.

Photophysical Properties and Photobiological Activities of Ruthenium(II) Complexes Bearing π-Expansive Cyclometalating Ligands with Thienyl Groups.

A new family of cyclometalated ruthenium(II) complexes [Ru(N^N)2(C^N)]+ derived from the π-extended benzo[h]imidazo[4,5-f]quinolone ligand appended with thienyl groups (n = 1-4, compounds 1-4) was prepared and its members were characterized for their chemical, photophysical, and photobiological properties. The lipophilicities of 1-4, determined as octanol-water partition coefficients (log Po/w), were positive and increased with the number of thienyl units. The absorption and emission bands of the C^N compounds were red-shifted by up to 200 nm relative to the analogous Ru(II) diimine systems. All of the complexes exhibited dual emission with the intraligand fluorescence (1IL, C^N-based) shifting to lower energies with increasing n and the metal-to-ligand charge transfer phosphorescence (3MLCT, N^N-based) remaining unchanged. Compounds 1-3 exhibited excited state absorption (ESA) profiles consistent with lowest-lying 3MLCT states when probed by nanosecond transient absorption (TA) spectroscopy with 532 nm excitation and had contributions from 1IL(C^N) states with 355 nm excitation. These assignments were supported by the lifetimes observed (<10 ns for the 1IL states and around 20 ns for the 3MLCT states) as well as a noticeable ESA for 3 with 355 nm excitation that did not occur with 532 nm excitation. Compound 4 was the only member of the family with two 3MLCT emissive lifetimes (15, 110 ns), and the TA spectra collected with both 355 and 532 nm excitation was assigned to the 3IL state, which was corroborated by its 4-6 μs lifetime. The ESA for 4 had a rise time of approximately 10 ns and an initial decay of 110 ns, which suggests a possible 3MLCT-3IL excited state equilibrium that results in delayed emission from the 3MLCT state. Compound 4 was nontoxic toward human skin melanoma cells (SKMEL28) in the dark (EC50 = >300 μM); 1-3 were cytotoxic and yielded EC50 values between 1 and 20 μM. The photocytotoxicites with visible light ranged from 87 nM with a phototherapeutic index (PI) of 13 for 1 to approximately 1 μM (PI = >267) for 4. With red light, EC50 values varied from 270 nM (PI = 21) for 3 to 12 μM for 4 (PI = >25). The larger PIs for 4, especially with visible light, were attributed to the much lower dark cytotoxicity for this compound. Because the dark cytotoxicity contributes substantially to the observed photocytotoxicity for 1-3, it was not possible to assess whether the 3IL state of 4 led to a much more potent phototoxic mechanism in the absence of dark toxicity. There was no stark contrast in cellular uptake and accumulation by laser scanning confocal and differential interference contrast microscopy to explain the large differences in dark toxicities between 1-3 and 4. Nevertheless, the study highlights a new family of Ru(II) C^N complexes where π-conjugation beyond a certain point results in low dark cytotoxicity with high photocytotoxicity, opposing the notion that cyclometalated Ru(II) systems are too toxic to be phototherapeutic agents.

Effect of thienyl units in cyanoacrylic acid derivatives toward dye-sensitized solar cells

A series of heterocyclic donor-acceptor systems were synthesized and well characterized by using 1H, 13C NMR, FT-IR, and elemental analysis. They were designed to investigate the effect of thiophene and cyanoacrylic acid number units on the thermal, optical, electrochemical and finally photovoltaic properties of dye-sensitized solar cells prepared with the selected compounds. The effect of chemical structure on their properties was demonstrated. They showed the beginning of thermal decomposition between 230 and 270 °C. The compounds absorbed the radiation in the range of 300–500 nm or 200–400 nm. They were electrochemically active and varied in energy band gap from 3.40 to 1.58 eV. Additionally, their optimized geometry, HOMO–LUMO levels, ionization potential, and electron affinity were evaluated using density functional theory. The photovoltaic devices based on TiO2 sensitized with the obtained molecules exhibited low power conversion efficiency, which was the highest for the device containing the symmetrical molecule with bithiophene structure. Under co-sensitization, the cell made of the same compound gave significant enhancement of efficiency of 6.3% being higher to that of the individual device prepared from dye N719 (5.75%). Moreover, the effects of immersion time of TiO2 electrode in the dye solution and co-sensitization methods were tested. The surface morphology of photoanode was investigated using atomic force microscopy.

π‐Dimerization ability of conjugated oligomer dication diradicaloids composed of dithienylpyrrole and benzodithiophene units

AbstractStable conjugated oligomer dications 12+ and 22+ composed of 2,5‐di(2‐thienyl)‐N‐methylpyrrole (DTP) units at the both ends of the π‐systems with methoxy substituents at the 3‐position of thienyl units and methylthio end‐capping group and benzo[2,1‐b:3,4‐b′]dithiophene (BDT) unit(s) at the central part with sterically demanding phenyl substituents were synthesized. From DFT calculations and ESR experiments, it was concluded that the diradical character in 12+ and 22+ was reduced in comparison with the radical character of their reference compound 3·+ composed of one DTP and one BDT units. In addition, the shorter 12+ was considered to have a further lower diradical character than that of 22+. Nevertheless, judging from the results of VT‐UV‐vis‐NIR measurements, both 12+ and 22+ showed a comparable π‐dimerization ability at the DTP moiety in dichloromethane solution with 3·+.

Assessing the Structure of Octastate Molecular Switches Using 1H NMR Density Functional Theory Calculations

Density functional theory calculations are used to reveal the relationships between the structures, energies, and NMR signatures of an octastate molecular switch composed of a dithienylethene (DTE) unit covalently linked to an indolino[2,1-b]oxazolidine (BOX) moiety through an ethylenic junction. Both the DTE and BOX moieties can adopt open or closed forms. The ethylenic junction can be Z or E, but the latter has been confirmed to be, by far, more stable than the former for all BOX/DTE combinations. In addition, when the DTE is open, the two thienyl units can fold to form parallel conformers, by opposition to the antiparallel or unfolded conformers. Usually parallel conformers present a higher energy than the antiparallel ones, but in the case of compound 2 having a bulky substituent (R = pPh-SMe) on the terminal thienyl group, the enthalpy of one conformer is very close (1–2 kJ mol–1) to that of the most stable antiparallel one, making photocyclization less efficient. These conformational differences and...

A Comparative Study on Two RuII Complexes with Thiophene‐Based Ancillary Ligands for High‐Efficiency Dye‐Sensitized Solar Cells

Heteroleptic polypyridyl Ru complexes MMR‐1 and MMR‐2 containing 2‐(methylthio)thienyl and 2‐(4‐methoxyphenyl)thienyl units on the antennas of ancillary ligands, respectively, were designed, synthesized, and characterized as sensitizers for dye‐sensitized solar cells. The maximum absorption wavelength of MMR‐1 is more red‐shifted than that of MMR‐2, but MMR‐2 has a higher molar extinction coefficient, leading to better light harvesting. Under the same device‐fabrication conditions, the photovoltaic performances of these sensitizers were evaluated while anchored on mesoporous TiO2 and compared to that of the benchmark N719. Both MMR‐1 and MMR‐2 exhibited comparable or even higher solar‐to‐electric conversion efficiencies η with respect to N719 when employed as photosensitizers in DSSCs. Compared to MMR‐1, MMR‐2 exhibited better overall conversion efficiency, which was attributed to the electron‐donating effect of the 4‐methoxyphenyl group and the better absorptivity by harvesting higher‐energy photons. Complex MMR‐2 also showed higher open‐circuit voltage VOC than MMR‐1, which is likely due to the extension of the antenna of the ancillary ligand by inserting a phenyl group, which leads to less dye aggregation. The photovoltaic performance of MMR‐2 was better, with a short‐circuit photocurrent density of 16.76 mA cm–2, a VOC of 0.673 V, a fill factor of 73.5 %, and an η value of 8.29 % with the addition of 0.5 m 4‐tert‐butylpyridine (TBP) compared to 8.18 % for N719.

Thienylquinonoidal Porphyrins and Hexaphyrins with Singlet Diradical Ground States.

To explore stable organic diradicaloids, meso-thienylquinonoid-substituted porphyrins Pn and hexaphyrins Hn, where "n" denotes the number of thienyl units in the meso-substituents, were synthesized. P0 was identified as a closed-shell quinonoid, whereas P1 was shown to possess significant diradical character with diradical character index (y) of 0.99 and quite small singlet-triplet energy gap (ΔES-T ) of -0.13 kcal mol-1 . P1 was certainly stable, allowing its isolation, but decomposed gradually in solution. In the hexaphyrin series, it was shown that H0 and H1 were closed-shell quinonoids, but H2 was a highly stable diradicaloid with y=0.85 and ΔES-T of -3.72 kcal mol-1 . The high stability of H2 was ascribed to effective spin delocalization over the entire conjugated network. Characteristically, H2 displays an intense absorption band in NIR region at λmax =1175 nm with molar absorption coefficient (ϵ) of 8.81×104 mol-1 L cm-1 , a narrow HOMO-LUMO gap of 0.69 eV, and nine reversible redox potential waves.

Polymers with Alkylsulfanyl Side Chains for Bulk Heterojunction Solar Cells: Toward a Greener Strategy

The synthesis and properties of three copolymers obtained through a Knoevenagel polycondensation are reported. They are soluble in organic solvents, filmable, and solvatochromic. They are characterized through gel permeation chromatography, NMR and UV–vis spectroscopies, cyclic voltammetry, and atomic force microscopy. They display some proneness to form π-stacks, broad absorptions up to about 700 nm, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies that fit those of [6,6]-phenyl-C61-butyric acid methyl ester ([60]PCBM). The polymers are incorporated in blends with PCBM within bulk heterojunction devices. The best results are found for polymer solar cells obtained from P1 (2.7% power conversion efficiency). The insertion of alkylsulfanyl chains improves the photovoltaic performances, with respect to those of alkyl-substituted analogous polymers. The Jsc of the devices are greatly enhanced, supporting the employment of (alkylsulfanyl)thienyl units as base units in photoactive materials.

Preparation and photovoltaic properties of pyrene-thieno[3,4-c]pyrrole-4,6-dione-based donor-acceptor polymers

Four new donor-acceptor conjugated copolymers, containing pyrene moieties flanked by thienyl or bithienyl groups as a donor units and thieno[3,4-c]pyrrole-4,6-dione (TPD) as acceptor units, were successfully prepared via a direct arylation polymerisation method. While all polymers prepared had 2-ethylhexyloxy-substituents on the pyrene repeat units, two different alkyl-substituents (octyl or 4-hexylphenyl groups) were attached to their TPD moieties. The influence of these different substituents as well as the number of thienyl units linking the pyrene and TPD units along polymer chains on the photophysical, electronic and photovoltaic properties of these materials was investigated. All polymers displayed good thermal stability up to 315°C. The optical band gap of the four polymers, PPEHDT-TPDO, PPEHDT-TPDHP, PPEHDT2-TPDO and PPEHDT2-TPDHP, were estimated to be 2.00, 2.06, 1.94 and 1.91eV, respectively. Polymers that possessed a single thiophene unit attached to the pyrene unit, PPEHDT-TPDO and PPEHDT-TPDHP, displayed deeper HOMO levels compared to those with bithiophene units, PPEHDT2-TPDO and PPEHDT2-TPDHP. Photovoltaic devices were fabricated from all polymers. PPEHDT2-TPDO boasted the highest efficiency with a PCE (2.06%), a FF of 53.07%, a Jsc of 4.66mA/cm2 and a Voc of 0.83V.

Inserting Thienyl Linkers into Conjugated Molecules for Efficient Multilevel Electronic Memory: A New Understanding of Charge-Trapping in Organic Materials.

The practical application of organic memory devices requires low power consumption and reliable device quality. Herein, we report that inserting thienyl units into D-π-A molecules can improve these parameters by tuning the texture of the film. Theoretical calculations revealed that introducing thienyl π bridges increased the planarity of the molecular backbone and extended the D-A conjugation. Thus, molecules with more thienyl spacers showed improved stacking and orientation in the film state relative to the substrates. The corresponding sandwiched memory devices showed enhanced ternary memory behavior, with lower threshold voltages and better repeatability. The conductive switching and variation in the performance of the memory devices were interpreted by using an extended-charge-trapping mechanism. Our study suggests that judicious molecular engineering can facilitate control of the orientation of the crystallite in the solid state to achieve superior multilevel memory performance.

Synthesis and photovoltaic properties of low bandgap dimeric perylene diimide based non-fullerene acceptors

Non-fullerene organic acceptors have attracted increasing attention in recent years. One of the challenges in the synthesis of non-fullerene organic acceptors is to tune the absorption spectrum and molecular frontier orbitals, affording low bandgap molecules with improved absorption of the near-infrared solar photons. In this paper, we present the synthesis, optoelectronic and photovoltaic properties of a series of dimeric perylene diimide (PDI) based non-fullerene acceptors. These PDI dimers are bridged by oligothiophene (T) from 1T to 6T. With the increase of the oligothienyl size, the highest occupied molecular orbital (HOMO) energy is raised from −5.65 to −5.10 eV, while that of the lowest unoccupied molecular orbit (LUMO) is kept constant at −3.84 eV, affording narrow bandgap from 1.81 to 1.26 eV. The absorption from the oligothiophene occurs between 350 and 500 nm, which is complementary to that from its bridged PDI units, leading to a wide spectral coverage from 350 to 850 nm. The optimal dihedral angle between the bridged two perylene planes is dependent on the oligothienyl size, varying from 5° to 30°. The solubility of the dimers depends on the oligothienyl size and can be tuned by the alkyl chains on the bridged thienyl units. The possible applications as the solution-processable non-fullerene organic acceptor is primarily studied using commercial P3HT as the blend donor. The photovoltaic results indicate that 1T, 4T and 6T all yield a higher efficiency of ∼1.2%, whereas 2T, 3T and 5T all give a lower efficiency of <0.5%. The difference in the cell performance is related with the tradeoff between the differences of absorption, HOMO level and film-morphology between these dimers.

Series of Quinoidal Methyl-Dioxocyano-Pyridine Based π-Extended Narrow-Bandgap Oligomers for Solution-Processed Small-Molecule Organic Solar Cells

Small molecules with narrow bandgap of <1.6 eV can harvest the visible and near-infrared solar photons. In this Article, we report a new method to achieve narrow bandgap small molecule donors by using electron-deficient quinoidal methyl-dioxocyano-pyridine (MDP) to induce possible quinoidal resonance structure along the conjugated A-pi-D-pi-A backbone. Practically, two MDP moieties are covalently linked onto an electron-rich benzodithiophene (BDT) through the oligothiophene (OT-5T) pi-bridge. The affording small molecules, namely, nTBM, exhibit broad and strong absorption bands covering the visible and near-infrared region from 400 to 870 nm. The estimated optical bandgap is down to 1.4 eV. The narrow bandgap is associated with the low-lying lowest unoccupied molecular orbital (LUMO) energy level (about -3.7 eV) and the high-lying highest occupied molecular orbital (HOMO) energy level (around -5.1 eV). Density-functional theory calculations reveal that the HOMO and LUMO energy levels, with the increase of the size of the oligothiophene bridge, become localizations in different moieties, i.e., the central electron-donating and the terminal electron-withdrawing units, respectively, which provides necessary driving force for the delocalization of the excited electrons and formation of the quinoidal resonance structure. The quinoidal structure enhances the photoinduced intramolecular charge-transfer, leading to the absorbance enhancement of the low-energy absorption band. With the increase of the size of the oligothiophene from 0 to 5 thienyl units and the change of the direction of the alkyl chains on the bridged thiophene from outward to inward, the crystalline nature, fibril length, and phase size of the blend films as well as the cell performance are all fine-tuned, also. With the inward alkyl chains, the terthiophene bridged molecule is amorphous, while the pentathiophene bridged one is relatively crystalline. Both molecules form nanoscale interpenetrating networks with a phase size of 15-20 nm when blended with PC71BM, showing the higher hole mobility and promising electric performance.

Synthesis and properties of D–A copolymers based on dithienopyrrole and benzothiadiazole with various numbers of thienyl units as spacers

By introducing different numbers of thienyl spacers, the properties of D–A type polymers could be modulated, which provides a simple strategy for designing high-performance D–A type photovoltaic polymers based on the existing polymers.

Synthesis, Electronic Structure, and Charge Transport Characteristics of Naphthalenediimide‐Based Co‐Polymers with Different Oligothiophene Donor Units

Naphthalenediimide (NDI)‐based polymers co‐polymerized with thienyl units are an interesting class of polymer semiconductors because of their good electron mobilities and unique film microstructure. Despite these properties, understanding how the extension of the thienyl co‐monomer affects charge transport properties remains unclear. With this goal in mind, we have synthesized a series of NDI derivatives of the parent poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene) (P(NDI2OD‐T2)), which exhibited excellent electron mobility. The strategy comprises both the extension of the donor o‐conjugation length and the heteroatomic fusion of the thiophene rings. These newly synthesized compounds are characterized experimentally and theoretically vis‐à‐vis with P(NDI2OD‐T2) as the reference. UV‐vis data and cyclic‐voltammetry are adopted to assess the effect of the donor modification on the frontier energy levels and on the bandgap. Intra‐molecular polaronic effects are accounted for by computing the internal reorganization energy with density functional theory (DFT) calculations. Finally electrons and holes transport is experimentally investigated in field‐effect transistors (FETs), by measuring current‐voltage characteristics at variable temperatures. Overall we have identified a regime where inter‐molecular effects, such as the wavefunction overlap and the degree of energetic disorder, induced by the different donor group prevail over polaronic effects and are the leading factors in determining electrons mobility.

Donor‐Acceptor Oligomers and Polymers Composed of Benzothiadiazole and 3‐Hexylthiophene: Effect of Chain Length and Regioregularity

AbstractA series of donor‐acceptor oligomer OBTThn (n=1–7) and polymer PBTTh1 and PBTTh2 composed of alternative 2,1,3‐benzothiadiazole and 3‐hexylthiophene have been designed and synthesized for the purpose of investigation on the effect of chain length and side‐chain regioregularity on their basic properties and photovoltaic performance. In the OBTThn oligomers and PBTTh1 polymer, all the hexyl side chains on thienyl units orient toward the same direction. Upon elongation of the chain length, the intramolecular charge transfer (ICT) absorption band in solution gradually redshifts from 398 nm for OBTTh1 to 505 nm for OBTTh7, then to 512 nm for PBTTh1 polymer. Meanwhile, the HOMO energy level increases from −5.45 eV (OBTTh1) to −5.08 eV (OBTTh7) and −5.09 eV (PBTTh1), and the LUMO energy level decreases from −3.11 eV (OBTTh1) to −3.30 eV (OBTTh7) and −3.33 eV (PBTTh1), thus giving a smaller and smaller energy bandgap for higher oligomers and polymers. Theoretical calculation suggests straight line‐like backbone geometry for this series of oligomers and polymer. On the other hand, polymer PBTTh2 possesses a different side‐chain regioregularity, in which every two neighbor hexyl side chains are arranged in different orienting direction. It is theoretically suggested to have curved line‐like backbone geometry. In solution, it shows similar photophysical and electrochemical properties as PBTTh1. However in film state, it displays a less redshift in the ICT band as refer to that in solution than PBTTh1. In combination with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM), these oligomers and polymers were used as donor material to fabricate organic bulk heterojunction solar cells. Again, chain length‐dependent device photovoltaic performance was observed. The device based on OBTTh4 showed a power conversion efficiency of 0.16%, while it increased to 0.36% and 0.49% for the devices based on OBTTh6 and PBTTh1, respectively. However, the side‐chain regioregularity has less influence on the device photovoltaic output since the device based on PBTTh2 displayed an efficiency of 0.52%, comparable to that of PBTTh1.