Electrochromic polyiminocarbazolylenes with latent hydrogen bonding

Abstract

Polyiminoarylenes with carbazole (cbz) units in the main chain, or main and side chain and thermally cleavable t-butyloxycarbonyl (boc) groups were prepared upon palladium-catalyzed coupling reactions. Polymers were prepared from 2,7-dibromo-9-(2-ethylhexyl)-carbazole M1 and 9-(4-aminophenyl)carbazole hydrochloride M3 (P1-EH), 2,7-dibromo-9-t-butyloxycarbonyl-carbazole M2 and M3 (P1-BOC), M1 and 4-t-butylaniline M4 (P2-EH), or M2 and M3 (P2-BOC). Thermal treatment of boc-substituted polymers P1-BOC and P2-BOC at 180°C for ≥4 h led to removal of the boc groups and formation of insoluble polymers P1-H and P2-H with strong adhesion to the substrate due to hydrogen bonding ('latent hydrogen bonding'). For P1-BOC the rate constant k of deprotection could be determined to be about 0.050 min −1 . Size exclusion chromatography indicated that the molecular weights of the polymers were between 14 100 and 28 100 g mol −1 . Polymers P1-EH, P1-BOC, P2-EH and P2-BOC were readily soluble in toluene, THF, dichloromethane, chloroform, and benzene, and insoluble in acetone and methanol.After removal of the boc groups the resulting polymer films of P1-H and P2-H were insoluble in common organic solvents. Optical and electrochemical properties of the polymers were investigated. Due to the electron-rich nitrogen atoms in the main chain, the polymers can be easily oxidized. Oxidation starts at about 0.31 V vs. SCE with formation of cation radicals. Further oxidation occurs at 0.55 V with formation of dications, and at 0.71 V with oxidation of main chain cbz units. At about 1 V the side chain cbz units are oxidized. The polymers are electrochromic and exhibit color changes from colorless via orange to green and blue. Cbz oxidation at potentials ≥0.71 V leads to the formation of dimers in a side reaction. Thermal cleavage of the boc groups leads to well-adhering films of P1-H and P2-H due to hydrogen bonding of the carbazole N-H-groups between polymer chains, and polymer and ITO-substrate. The best performance with regard to reversible oxidation and adhesion was found for P1-H. For this polymer a reversible electrochromism was found. A contrast ratio of 12% at 900 nm, and a switching time of 400 ms were determined.

Hydrogen-Bonding-Mediated Solid-State Self-Assembled Isoepindolidiones (isoEpi) Crystal for Organic Field-Effect Transistor

“…The tert -butyloxycarbonyl ( t -Boc) substituted isoEpi (isoEpi-Boc) was synthesized by following the previous reported method for similar molecules. , The two t -Boc units on isoEpi-Boc blocked the hydrogen bonding, and thus rendered the molecule soluble in common organic solvents. The side chain of isoEpi-Boc could be removed to generate original pigment, releasing isoprene and carbon dioxide (Supporting Information, Figure S2).…”

Crystalline Organic Pigment-Based Field-Effect Transistors

“…This “latent hydrogen bonding” was first reported in DPP pigments . It was recently used in several conjugated polymers to form latent hydrogen bonding-based polymers. − As crystallinity is pivotal for small-molecule OFET devices, a crystal-to-crystal transition method was developed in this work to fabricate crystalline pigment OFET devices. The single crystals of soluble pigment precursors were obtained by slow evaporation; after a simple thermal annealing procedure, the solubilizing groups were removed and the soluble pigment precursors with latent hydrogen bonding were converted into the original pigment molecules with fused hydrogen bonding.…”

3,6-Carbazole vs 2,7-carbazole: A comparative study of hole-transporting polymeric materials for inorganic–organic hybrid perovskite solar cells

“…In contrast, the poly(2,7-carbazole) derivatives appeared after the pioneering synthetic studies of the 2,7-dihalogeno-carbazole monomers [26–27]. A series of 2,7-carbazole-based copolymers were synthesized, and most of them showed better semiconducting properties in organic field effect transistors (OFETs), bulk-heterojunction (BHJ) solar cells, thermoelectric and electrical memory devices as compared to the counter 3,6-carbazole-based polymers [28–36]. However, this structural relationship between the 3,6-carbazole and 2,7-carbazole has not yet been eluciated in the PSCs because of the emerging new devices.…”