A Two-Dimensional Poly(azatriangulene) Covalent Organic Framework with Semiconducting and Paramagnetic States

Abstract

The black crystalline (aza)­triangulene-based covalent organic framework TANG-COF was synthesized from its trinitro-TANG precursor via a one-pot, two-step reaction involving Pd-catalyzed hydrogenation and polycondensation with an aromatic dialdehyde. High crystallinity and permanent porosity of the layered two-dimensional (2D) structure were established. The rigid, electron-rich trioxaazatriangulene (TANG) building block enables strong π-electron interactions manifested in broad absorptions across the visible and NIR regions (E g ≈ 1.2 eV). The high HOMO energy of TANG-COF (−4.8 eV) enables facile p doping, resulting in electrical conductivity of up to 10–2 S/cm and room-temperature paramagnetic behavior with a spin concentration of ∼10%. DFT calculations reveal dispersion of the highest occupied band both within the 2D polymer layers (0.28 eV) and along their π-stacked direction (0.95 eV).

Syntheses and Properties of (Nitronyl nitroxide)‐substituted Tri‐phenylamine ortho‐Bridged by Two Oxygen and Sulfur Atoms

“…We previously reported that radical‐substituted donor NN‐TOT produced stable radical‐substituted radical cation salts upon selective oxidation of the donor unit due to the superior electron‐donating nature of TOT (Figure 1). [5,10,11] Importantly, the diradical cationic species, NN‐TOT + is indicated as being present in the triplet ground state with quite large intramolecular exchange interactions. In addition, diradial cation salt NN‐TOT + ⋅ GaCl 4 − exhibited a magnetic phase transition at T =2.65 K from a short‐range‐ordered antiferromagnetic chain to a three‐dimensional weak ferromagnet [5] .…”

Two dimensional semiconducting polymers

“…Moreover, they found that doped P11 showed a paramagnetic property under cryogenic conditions. 63 Triazine-containing conjugated polymers have been promising for versatile applications due to their nitrogen-rich optoelectronic nature. The traditional synthetic methods require the monomers to bear a high temperature or strong acid treatment, which limits the choices of monomers.…”

“…(e and f) Temperature dependence of (e) the spin susceptibility and (f) the ESR line width. Reprinted with permission from ref 63,. Copyright 2020, American Chemical Society.…”

Unraveling the Effect of Defects, Domain Size, and Chemical Doping on Photophysics and Charge Transport in Covalent Organic Frameworks

“…Formation of "hole" polarons in organic materials, optically (e.g., by photoinduction), electrochemically (e.g., by applying gate voltage) or in the presence of chemical dopants, gives rise to significant absorption in the mid-IR energy range, which is characterized by a lowenergy peak A (0.05-0.2 eV), dressed with intramolecular vibrations (IRAVs), and a much broader higher energy peak B (> 0.25 eV ). [25][26][27][28][29][30][31] The A peak is labelled as DP 1 (delocalized polaron) 26,32 or CT (charge transfer), 25,33,34 while the B peak is commonly referred to as P1 25,26,30 in the conventional polaron model. In conjugated polymers, such as P3HT, a redshift of peak B(P1) is either related to increased polaron delocalization lengths [26][27][28]30,35 or the formation of spin-less non-radical bipolarons.…”

“…37 The characteristic low energy-peak A and the blue-shifted broad peak B is evident in the mid-IR absorption spectra of iodine doped (aza)triangulene-based COF (TANG-COF) which exhibit high inand out-of-plane conductivity. 31 COFs exhibit a dramatic but reversible increase in conductivity upon exposure to iodine. 11,[38][39][40] Vapor doping tetrathiafulvalene-based COFs with iodine results in a significantly larger increase in conductivity compared to solution doping with TCNQ.…”