Abstract:
Synthesis of covalent organic framework (COF)
thin films on different supports with high crystallinity and porosity
is crucial for their potential applications. We have designed a new
synchronized methodology, residual crystallization (RC), to
synthesize sub 10 nm COF thin films. These residual crystallized
COF thin films showcase high surface area, crystallinity, and
conductivity at room temperature. We have used interfacial
crystallization (IC) as a rate-controlling tool for simultaneous
residual crystallization. We have also diversified the methodology
of residual crystallization by utilizing two different crystallization
pathways: fiber-to-film (F−F) and sphere-to-film (S−F). In both
cases, we could obtain continuous COF thin films with high
crystallinity and porosity grown on various substrates (the highest
surface area of a TpAzo COF thin film being 2093 m2 g−1
). Precise control over the crystallization allows the synthesis of
macroscopic defect-free sub 10 nm COF thin films with a minimum thickness of ∼1.8 nm. We have synthesized two COF thin films
(TpAzo and TpDPP) using F−F and S−F pathways on different supports such as borosilicate glass, FTO, silicon, Cu, metal, and
ITO. Also, we have investigated the mechanism of the growth of these thin films on various substrates with different wettability.
Further, a hydrophilic support (glass) was used to grow the thin films in situ for four-probe system device fabrication. All residual
crystallized COF thin films exhibit outstanding conductivity values. We could obtain a conductivity of 3.7 × 10−2 mS cm−1 for the
TpAzo film synthesized by S−F residual crystallization.
