Triazine and Porphyrin-Based Cross-Linked Conjugated Polymers: Protonation-Assisted Dissolution and Thermoelectric Properties

Abstract

Triazine and porphyrin as two pivotal functional segments are coupled to form a highly cross-linked conjugated polymer. Although the obtained conjugated polymers are almost insoluble in most solvents, a small amount of protonic acid can cause the formation of a colloidal solution of polymers. The dissolution process is proved to be a surface charge effect induced by protonation of porphyrin units in the polymer frameworks. High-quality conjugated polymer films are prepared on diverse substrates by solution drop-casting and used for thermoelectric application. The films exhibit remarkable thermoelectric performance with high Seebeck coefficient (-6650 μV K-1) and electronic conductivity (0.042 S cm-1), yielding a power factor of 185 W m-1 K-2 , which are the highest among all reported n-type organic thermoelectric materials. This work may pave the way for the design and development of solution-processed crosslinked polymer films as promising thermoelectric materials.

Electrocleavage Synthesis of Solution-Processed, Imine-Linked, and Crystalline Covalent Organic Framework Thin Films

“…The electrocleavage synthesis was monitored by cyclic voltammetry (CV) in the potential range from 0 to −2.0 V. From the first cycle of the negative scan, the onset potential at −0.78 V accounted for the reduction of the imine bonds with the formation of amine bonds (Figure a), followed by protonation by PTSA to generate protonated amine bonds. This process introduced a large number of positive charges to the COF skeletons and exfoliated the COF powders into nanosheets by electric repulsion . The charged nanosheets were highly dispersible in the electrolyte solution, which made the color of the electrolyte solution change from colorless to light orange, as could be directly visualized by naked eyes.…”

“…This process introduced a large number of positive charges to the COF skeletons and exfoliated the COF powders into nanosheets by electric repulsion. 20 The charged nanosheets were highly dispersible in the electrolyte solution, which made the color of the electrolyte solution change from colorless to light orange, as could be directly visualized by naked eyes. On the subsequent positive scan, oxidation with an onset potential of −1.0 V and a peak potential of −0.5 V was observed, which could be assigned to the oxidation of the positively charged amine bonds generated in the former scan to obtain neutral imine bonds.…”

Solution Processing of Cross-Linked Porous Organic Polymers

“…We first screened our solution-processed CPOP films by measuring their conductivities and finalized Por-CTF for this purpose. 40 When manipulating the temperatures of the two sides of the device to a constant gradient of 10 K (Figure 6g), the device based on the protonated Por-CTF film exhibited substantial conductivity increment accompanied by the increased relative humidity (RH), indicating that the observed conductivity involved the contributions from both electric and ionic conductions. After excluding the ionic conductivity by measuring the impedance spectra, the electric conductivity showed a substantial increment along with increasing the protonation degree.…”

“…We call this the in situ protonation approach (Figure a). To verify this approach, we chose cyano groups as the reaction sites, which undergo trimerization to form triazines upon superacid catalysis; dihydrophenazine and porphyrin were selected as the cores, which were demonstrated to be readily protonated. , Accordingly, DHPAZ-CTF and Por-CTF (CTF = covalent triazine framework) were directly synthesized as dispersible sols in CF 3 SO 3 H solutions (Figure b,c), followed by precipitating from the solutions upon neutralization with bases. , The CTFs could readily disperse in polar solvents to form transparent, stable, and solution-like sols by additional protonation assisted by various acids (Figure b,c), with fine controllability over the dispersibility by manipulating the protonation degree. For instance, the dispersibility of Por-CTF reached as high as 88.7 mg mL –1 when adding 24.3 mol % CF 3 SO 3 H .…”

Understanding the Temperature Dependence of the Seebeck Coefficient from First-Principles Band Structure Calculations for Organic Thermoelectric Materials

“…Organic thermoelectric materials (OTEs) have aroused great interests and have been developed rapidly in recent years [1][2][3][4][5][6][7] . Compared with inorganic thermoelectric materials, OTEs is lower thermally conductive, more cost-effective and less toxic.…”