Terahertz (THz) spectroscopy is an emerging tool for probing charge transport and optical properties in covalent organic frameworks (COFs). Existing studies have predominantly relied on time-resolved THz spectroscopy (TRTS) to investigate photoexcited carriers, with only one report on time-dependent THz spectroscopy (TDTS) to understand ground-state carriers within a narrow spectral window. Frequency-domain THz spectroscopy (FDTS), which offers high spectral resolution across the far-infrared-THz range remains unexplored. Herein, we employ FDTS to investigate steady-state carrier transport in a COF (TTC-PD) and amorphous frameworks (TTC-DTO and TTC-PD (amor)), along with their molecular analogues. Frequency-dependent optical constants and complex conductivity were extracted using Kramers-Kronig transformations (KKT) and validated by TDTS. Despite stronger carrier localization, TTC-DTO exhibits higher intrinsic conductivity due to increased carrier density, whereas TTC-PD shows lower conductivity but higher mobility arising from more delocalized transport pathways. This conceptual study demonstrates the potential of FDTS and TDTS as a combined and complementary platform for comprehensive analysis of the ground state charge transport properties of frameworks across the extended THz regime.
Nath et al. (Fri,) studied this question.