A Thiophene, Benzothiadiazole, and Carbazole-Based Copolymer : Synthesis and Characterization

Abstract

Of the various types of polymerbased, photovoltaic devices designed to date, the most efficient photovoltaic devices, having power conversion efficiencies (PCEs) of 3-4%, were fabricated using a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron-donor and electron-acceptor materials, respectively.1,2 Soon after the initial reports, P3HT/PCBM-based photovoltaic devices were optimized to achieve PCEs approaching 5%.3-5 New p-type polymers, which absorb light more broadly in the terrestrial solar radiation spectrum, were needed to increase the PCE of these photovoltaic devices. The HOMO/LUMO energy levels and the charge mobility of new p-type materials should also be optimized as these properties are intimately related to photovoltaic performance, as proposed by Scharber et al. 6 Benzothiadiazole (BT) is a well-known electron-deficient molecule which can be conjugated with an electron-rich molecule to form oligomers or polymers with small band gap energies, 7,8 and several different polymers of this variety have been synthesized for applications in electronic devices. 9,10 Recently, Heeger and coworkers used a polymer of alternating cyclopentadithiophene and dibenzothiadiazole units in the fabrication of photovoltaic cells, yielding a PCE of 5%. 11Carbazole derivatives have a planar conjugated structure and good hole transporting properties as well as electron-donating properties.12 Blouin and coworkers have synthesized copolymers bearing carbazole units and employed them in the fabrication of photovoltaic devices with PCEs reaching to 3.6%. 13It appeared interesting to study polymers bearing thiophene-carbazole derivatives and BT as electron-releasing and electron-withdrawing units, respectively, in a polymer backbone. Thus, the goal of this report is to report the synthesis of a conjugated polymer consisting of 3HT, BT, and 2-ethylhexylcarbazol (CZ) (P3HT2BTCZ) and describe the optical and electrochemical properties of the resulting polymer. Experimental SectionMaterials. 3-Hexylthiophene (3HT), carbazole, 2,1,3-benzothiadiazole, n-butyllithium (2.5 M in hexane), 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, tributyltin chloride, tetrakis(triphenylphosphine) palladium(0), tetrahydrofuran (THF), N-bromosuccinimide (NBS), potassium carbonate, bromine, hydrogen bromide, toluene, and chloroform were purchased from Aldrich and used without further purification. 4,7-Bis(5-bromo-4-hexylthiophene-2-yl)benzo[c][1,2,5]-thiadiazole (1).The synthetic procedure of compound 1 has been described elsewhere 14 (orange solid, 0.51 g, 85% yield). 3,6-Dibromocarbazole (2). Using a modified version of a previously reported method, 15 carbazole (16.7 g, 100 mmol) was dissolved in DMF (150 mL) at 0 o C with stirring, followed by the addition of a solution of NBS (36.3 g, 200 mmol) in 100 mL of DMF. The resulting mixture was stirred at room temperature for 2 hr, and the solution then poured into 1 L of water, filtered, and washed with water. The crude product was rec...

Sensitivity of Redox and Optical Properties of Electroactive Carbazole Derivatives to the Molecular Architecture and Methoxy Substitutions

“…The disubstituted compounds ( 2 , 3 ) were prepared in two steps, starting from anisole and carbazole derivatives, respectively, using the previously reported methods. − Tetramethoxycabazole ( 4 ) was obtained from the 2,7-dimethoxycarbazole, via bromination and methoxylation reactions.…”

Copolymers and Hybrids Based on Carbazole Derivatives and Their Nanomorphology Investigation

“…All other solvents and reagents were purchased from Aldrich (Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany ) or Alfa Aesar (Thermo Fisher (Kandel) GmbH Postfach, Karlsruhe, Germany) and were used without further purification unless otherwise stated. 6-Vinylphenyl-(2-pyridinyl)-4-phenyl-quinoline (vinyl-QPy) [36], 6-vinylphenyl-(2-perfluorophenyl)-4-phenyl-quinoline (vinyl-5FQ) [37], 4,7-di-2-thienyl-2,1,3-benzothiadiazole (di-thien-BTZ) [38,39], 4,7-di-(5-bromothiophene-2-yl-2,1,3-benzothiadiazole (di-Br-di-thien-BTZ) [40], 2,7-dibromo- N -heptadecan-9-yl-carbazole (di-Br-HD-carbazole) [41], 2,7-di(4,4,5,5-tetramethyl-1,3,2-dioxaborolan)-N-heptadecan-9-yl-carbazole (di-boronic ester-HD-carbazole) [41], 3,6-dibromo- N -2-ethylhexyl-carbazole (di-Br-EH-carbazole) [42], 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9″-(ethylhexyl) carbazole [43] and the catalyst palladium (II) tetrakis triphenyl phosphine (Pd(PPh 3 ) 4 ) [44] were synthesized according to published procedures.…”

Strategical Designing of Donor–Acceptor–Donor Based Organic Molecules for Tuning Their Linear Optical Properties

“…Although in recent years, a lot of emphasis has been paid on understanding the dependence of structural and electronic properties of D–A based organic molecules on the choice of donor and acceptor moieties and their configuration in the molecules. − But, in order to predict energy-efficiency of optoelectronic devices, optical absorption spectrum of these materials, especially in low energy region close to band edge, is highly desired. Among several investigated D–A molecules, ,,− thiophene benzothiadiazole based D–A molecules are found to be a popular choice. The benzothiadiazole group acts both as an electron transporting and highly fluorescent chromophore.…”