Synthesis and Aggregation Behavior of a Glycolated Naphthalene Diimide Bithiophene Copolymer for Application in Low-Level n-Doped Organic Thermoelectrics

Abstract

The synthesis of a naphthalene diimide bithiophene copolymer P­(EO-NDIT2) with branched, base-stable, and purely ether-based side chains is presented. Stille polycondensation leads to high molecular weights that are limited by methyl transfer and eventually T2 homocouplings. While extensive solution aggregation hampers molecular weight determination by conventional methods, NMR spectroscopy allows identification of both T2- (H and methyl) and NDI-related (methyl) end groups, enabling the determination of absolute number average molecular weights larger than M n,NMR ∼100 kg/mol. Solvent- and temperature-dependent aggregation in solution is investigated by NMR and UV–vis spectroscopy. These results are used for solution doping of P­(EO-NDIT2) with N-benzimidazole-based n-dopants. Spin coating from heated chlorobenzene solutions and using 4-(2,3-dihydro-1,3-dimethyl-1H-benzoimidazol-2-yl)-N,N-diisopropylaniline (N-DiPrBI) as the dopant leads to homogeneous films with highest conductivities up to 10–2 S/cm. Generally, N-DiPrBI concentrations as low as ∼5 wt % are sufficient to increase conductivity by orders of magnitude. Strikingly, maximum power factors up to 0.11 μW/mK2, although limited by conductivity, are achieved for the highest molar mass sample at a low dopant concentration of 2 wt % N-DiPrBI only.

The Effect of Alkyl Spacers on the Mixed Ionic‐Electronic Conduction Properties of N‐Type Polymers

“…This observation is in agreement with recent findings describing the synthesis of other NDI‐T2 copolymers with polar side chains containing an ester linkage. [ 36 ] Copolymerization via Stille coupling was carried out following an optimized protocol, which has been previously shown to increase the yield of the chloroform soluble fractions for p(gNDI‐gT2). [ 37 ] Accordingly, C3‐gNDI and C6‐gNDI were reacted with equimolar quantities of the stannylated comonomer gT2 in DMF at 80 °C to give p(C3‐gNDI‐gT2) and p(C6‐gNDI‐gT2) in a yield of 83% and 70%, respectively.…”

“…Similar findings have been previously reported when attempting to determine the molecular weight distribution of polymers with polar side chains by GPC or MALDI‐ToF measurements. [ 19,36,39 ] All polymers show good thermal stability with 5% weight‐loss temperatures above 300 °C, as determined by thermogravimetric analysis under inert atmosphere (Table 1; Figure S8, Supporting Information).…”

n-Type organic semiconducting polymers: stability limitations, design considerations and applications

“…In these cases, the common method of using size exclusion chromatography, which includes gel permeation chromatography (GPC), may not be sufficient, and alternative methods, such as end group NMR spectroscopy analysis, to identify the absolute number of protons and determine the molecular weight may be required. 22 A higher mobility is often recorded when defects and impurities in the material are minimised, thereby reducing the number of trapping sites and subsequently decreasing the number of immobile charge carriers. OSC polymers are most commonly semi-crystalline, with regions of crystallinity, dispersed in amorphous regions (Fig.…”

MALDI Matrices for the Analysis of Low Molecular Weight Compounds: Rational Design, Challenges and Perspectives

“…[3][4][5][6][7] The matrix is central to the MALDI process, and as analyte incorporation as well as the desorption and ionization efficiency can differ between given matrix/analyte pairs, choosing the right matrix is a key success driver in MALDI MS. [8] In the past decades, various matrices suitable for different macromolecule classes have been developed: For example, α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) are excellent and ubiquitously used matrices for proteins, peptides and polysaccharides, [9][10][11] while trans-2-[3-(4-t-butyl-phenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) has a high ionization efficiency for conjugated polymers. [12] While MALDI MS is a much relied-on standard tool for HMW analytics, LMW compounds (with m/z < 1000) -which cover a wide range of metabolite classes, e. g., amino acids, hormones, saccharides etc., are usually investigated with other MS methods. [13][14][15] But especially with the advance of MS imaging (MSI) techniques, there is now a significant interest to make LMW compounds analytics accessible with MALDI MS. MALDI-MSI is a simple, rapid and sensitive method to visualize the spatial distribution of interesting molecules, e. g., small pharmaceutical drugs, on tissue sections [16,17] and to trace metabolic pathways.…”

“…The matrix is central to the MALDI process, and as analyte incorporation as well as the desorption and ionization efficiency can differ between given matrix/analyte pairs, choosing the right matrix is a key success driver in MALDI MS [8] . In the past decades, various matrices suitable for different macromolecule classes have been developed: For example, α ‐cyano‐4‐hydroxycinnamic acid (CHCA) and 2,5‐dihydroxybenzoic acid (DHB) are excellent and ubiquitously used matrices for proteins, peptides and polysaccharides, [9–11] while trans‐ 2‐[3‐(4‐ t ‐butyl‐phenyl)‐2‐methyl‐2‐propenylidene]malononitrile (DCTB) has a high ionization efficiency for conjugated polymers [12] …”