Nonlinear Nonacenes with a Dithienothiophene Substructure: Multifunctional Compounds that Act as Columnar Mesogens, Luminophores, π Gelators, and p-Type Semiconductors

Board-like liquid-crystalline semiconductors based on the dithieno[3,2-b;2',3'-d]thiophene (DTT) substructure were synthesized and their thermal, self-assembly, optical, and semiconducting properties investigated. These sanidic compounds, bearing eight peripheral chains, are mesomorphic and spontaneously self-assemble into columnar hexagonal mesophases (Col_hex ) over broad temperature ranges, as confirmed by polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering. Strong blue photoluminescence with absolute quantum yields up to 33 % were measured. These compounds also form blue-light emitting gels in various organic solvents. The fibrillar-like morphology of these gels, reminiscent of the columnar structure, and stabilized by efficient intermolecular interactions, was characterized by scanning electron microscopy. The charge carrier mobility of these π-extended mesogens was measured by time-of-flight transient photocurrent technique in the Col_hex mesophase, and showed good hole-transport performance with charge carrier mobility of 10^-3  cm²  V^-1  s^-1 .

Following the TRMC Trail: Optimization of Photovoltaic Efficiency and Structure-Property Correlation of Thiophene Oligomers

Semiconducting conjugated oligomers having same end group (N-ethylrhodanine) but different central core (thiophene: OT-T, bithiophene: OT-BT, thienothiophene: OT-TT) connected through thiophene pi-linker (alkylated terthiophene) were synthesized for solution processable bulk-heterojunction solar cells. The effect of the incorporation of an extra thiophene to the central thiophene unit either through C-C bond linkage to form bithiophene or by fusing two thiophenes together to form thienothiophene on the optoelectronic properties and photovoltaic performances of the oligomers were studied in detail. Flash photolysis time-resolved microwave conductivity (FP-TRMC) technique shows OT-TT has significantly higher photoconductivity than OT-T and OT-BT implying that the former can outperform the latter two derivatives by a wide margin under identical conditions in a bulk-heterojunction solar cell device. However, the initial photovoltaic devices fabricated from all three oligomers (with PC71BM as the acceptor) gave power conversion efficiencies (PCEs) of about 0.7%, which was counterintuitive to the TRMC observation. By using TRMC results as a guiding tool, solution engineering was carried out; no remarkable changes were seen in the PCE of OT-T and OT-BT. On the other hand, 5-fold enhancement in the device efficiency was achieved in OT-TT (PCE: 3.52%, VOC: 0.80 V, JSC: 8.74 mA cm(-2), FF: 0.50), which was in correlation with the TRMC results. The structure-property correlation and the fundamental reasons for the improvement in device performance upon solvent engineering were deduced through UV-vis absorption, atomic force microscopy, bright-field transmission electron microscopy, photoluminescence quenching analysis and two-dimensional grazing incidence X-ray diffraction studies.

p/n-Polarity of thiophene oligomers in photovoltaic cells: role of molecular vs. supramolecular properties

Molecular and supramolecular properties play key roles in the optoelectronic properties and photovoltaic performances of organic materials. In the present work, we show how small changes in the molecular structure affect such properties, which in turn control the intrinsic and fundamental properties such as the p/n-polarity of organic semiconductors in bulk-heterojunction solar cells. Herein, we designed and synthesized two acceptor-donor-acceptor type semiconducting thiophene oligomers end-functionalized with oxazolone/isoxazolone derivatives (OT1 and OT2 respectively). The HOMO-LUMO energy levels of both derivatives were found to be positioned in such a way that they can act as electron acceptors to P3HT and electron donors to PCBM. However, OT1 functions as a donor (with PCBM) and OT2 as an acceptor (with P3HT) in BHJ photovoltaic cells, and their reverse roles results in either no or poor performance of the cells. Detailed studies using UV-vis absorption and fluorescence spectroscopy, time-correlated single photon counting, UV-photoelectron spectroscopy, density functional theory calculations, X-ray diffraction, and thermal gravimetric analysis proved that both molecular and supramolecular properties contributed equally but in a contrasting manner to the abovementioned observation. The obtained results were further validated by flash-photolysis time-resolved microwave conductivity studies which showed an excellent correlation between the structure, property, and device performances of the materials.

Synthesis and characterization of the regiorandom homopolymer of 3-alkyldithieno[3,2-b:2′,3′-d]thiophene for thin-film transistors

Regiorandom homopolymers of 3-alkyldithieno[3,2-b:2′,3′-d]thiophene were synthesized, characterized and used in OTFTs, showing an annealing-free hole mobility up to 0.048 cm² V⁻¹ s⁻¹.

Boron ketoiminate-based conjugated polymers with tunable AIE behaviours and their applications for cell imaging

A series of AIE-active D–A type conjugated polymers incorporating boron ketoiminate units were synthesized and applied for cell imaging.

Conjugated donor–acceptor copolymers derived from phenylenevinylene and trisubstituted pyridine units

Copolymers having intramolecular donor–acceptor systems encompassing trisubstituted pyridine derivatives as acceptor and phenylenevinylene (PPV) unit as a donor segment were synthesized. In addition, thiophene-containing random terpolymer PPVPYT via palladium-catalyzing Heck coupling reaction is reported. The novel-substituted pyridine monomers (PYBr) are synthesized by adopting a one-pot synthesis method using p-toluenesulfonic acid as catalyst in ethanol medium, which results in an excellent yield of about 95%. All the copolymers Poly phenylenevinylene-co-Pyridine derivatives (PPVPY) and terpolymers of Polyphenylenevinylene-co-Pyridine and Thiophene (PPVPYT) are found to be soluble in organic solvents, such as tetrahydrofuran, chloroform, and N, N-dimethylformamide. The molecular weights of the synthesized polymers were characterized by gel permeation chromatography (GPC), and their chemical structures were confirmed by infra red and nuclear magnetic resonance spectroscopies. The electrochemical band gaps of PPVPY-1, PPVPY-2, and PPVPY-3 copolymers are estimated to be 2.55, 2.48, and 2.0, respectively. Similarly, the band gap of PPVPY75T25, PPVPY50T50, and PPVPY25T75 random copolymers are estimated as 2.31, 1.95, and 2.23, respectively. These polymers also show excellent optical and thermal properties.