Use of a Multiple Hydride Donor To Achieve an n-Doped Polymer with High Solvent Resistance

Abstract

The ability to insolubilize doped semiconducting polymer layers can help enable the fabrication of efficient multilayer solution-processed electronic and optoelectronic devices. Here, we present a promising approach to simultaneously n-dope and largely insolubilize conjugated polymer films using tetrakis­[{4-(1,3-dimethyl-2,3-dihydro-1H-benzo­[d]­imidazol-2-yl)­phenoxy}­methyl]­methane (tetrakis-O-DMBI-H), which consists of four 2,3-dihydro-1H-benzoimidazole (DMBI-H) n-dopant moieties covalently linked to one another. Doping a thiophene-fused benzodifurandione-based oligo­(p-phenylenevinylene)-co-thiophene polymer (TBDOPV-T) with tetrakis-O-DMBI-H results in a highly n-doped film with bulk conductivity of 15 S cm–1. Optical absorption spectra provide evidence for film retention of ∼93% after immersion in o-dichlorobenzene for 5 min. The optical absorption signature of the charge carriers in the n-doped polymer decreases only slightly more than that of the neutral polymer under these conditions, indicating that the exposure to solvent also results in negligible dedoping of the film. Moreover, thermal treatment studies on a tetrakis-O-DMBI-H-doped TBDOPV-T film in contact with another undoped polymer film indicate immobilization of the molecular dopant in TBDOPV-T. This is attributed to the multiple electrostatic interactions between each dopant tetracation and up to four nearby anionic doped polymer segments.

Improving the Resistance of Molecularly Doped Polymer Semiconductor Layers to Solvent

“…19−22 We have recently reported that the tetrafunctional n-dopant tetrakis[(4-(1,3-dimethyl-2,3-dihydro-1Hbenzo[d]imidazol-2-yl)phenoxy)methyl]methane largely insolubilizes a thiophene-fused benzodifurandione-based oligo(pphenylenevinylene)-co-thiophene polymer in the original deposition solvent and have attributed this to the network of electrostatic interactions formed by the resulting tetracation and negatively charged polymer chain segments. 23 Here, we focus on the two above-mentioned mechanisms for enhancing the resistance of doped polymer layers against exposure to solvent, while also retaining the dopants: preaggregation-induced and cross-linking-induced layer retention are compared to clarify the interplay of these effects and to show their potential for the fabrication of multi-heterolayer structures. First, using 1,2,4,5,7,8-hexafluoro-11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (F 6 TCNNQ) as a molecular p-dopant, we show that the layer retention of P3HT can For the cross-linking approach, we use the photo-activated CLA benzene-1,3,5-triyl tris(4-azido-2,3,5,6-tetrafluorobenzoate).…”

“…Jacobs et al observed doping-induced layer retention in a wide range of solvents for poly­(3-hexylthiophene-2,5-diyl) (P3HT) sequentially doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) . Other studies on P3HT doped with tris­(pentafluorophenyl)­borane (BCF), F 4 TCNQ-doped poly­[2,5-bis­(3-dodecyl-2-thienyl)-thieno­(3,2- b )­thiophene] (C12-PBTTT), and poly­[2-methoxy-5-(2′-ethylhexyloxy)- p -phenylene vinylene] (MEH-PPV) have found aggregation of polymer chains already in solution after adding the molecular dopant to the polymer solution. − We have recently reported that the tetrafunctional n-dopant tetrakis­[(4-(1,3-dimethyl-2,3-dihydro-1 H -benzo­[ d ]­imidazol-2-yl)­phenoxy)­methyl]­methane largely insolubilizes a thiophene-fused benzodifurandione-based oligo­( p -phenylenevinylene)- co -thiophene polymer in the original deposition solvent and have attributed this to the network of electrostatic interactions formed by the resulting tetracation and negatively charged polymer chain segments …”

“… 19 − 22 We have recently reported that the tetrafunctional n-dopant tetrakis[(4-(1,3-dimethyl-2,3-dihydro-1 H -benzo[ d ]imidazol-2-yl)phenoxy)methyl]methane largely insolubilizes a thiophene-fused benzodifurandione-based oligo( p -phenylenevinylene)- co -thiophene polymer in the original deposition solvent and have attributed this to the network of electrostatic interactions formed by the resulting tetracation and negatively charged polymer chain segments. 23 …”

Thermal Insolubilization of Electrically n-Doped Films Achieved Using 7-Alkoxy-Benzocyclobutene-Substituted Fullerene and Dopant Molecules

“…We have recently reported simultaneous n-doping, insolubilization, and dopant immobilization in a conjugated polymer using postfilm-deposition thermal activation of a dopant that forms a large tetracation that acts to "electrostatically cross-link" polymer chains. 10 However, the formation of covalent bonds between semiconductors and dopants, and/or between adjacent semiconductor moieties, subsequent to film formation is, in principle, a more general and reliable approach to achieving these goals. Several examples of this approach have been reported for the case of fullerene semiconductors.…”

“…The use of large dopant molecules can in some cases lead to immobilization of the dopants; however, often the doped film remains substantially soluble in the types of organic solvent typically used to deposit subsequent layers. We have recently reported simultaneous n-doping, insolubilization, and dopant immobilization in a conjugated polymer using postfilm-deposition thermal activation of a dopant that forms a large tetracation that acts to “electrostatically cross-link” polymer chains . However, the formation of covalent bonds between semiconductors and dopants, and/or between adjacent semiconductor moieties, subsequent to film formation is, in principle, a more general and reliable approach to achieving these goals.…”