Extending the π-Conjugated System in Conjugated Microporous Polymers to Modulate Excitonic Effects for Metal-Free Selective CO₂ Photoreduction to CH₄

Abstract

Photocatalytic CO 2 reduction into CH 4 is an appealing approach to alleviate the current energy and environmental crisis; however, achieving high selectivity and conversion efficiency still remains challenging. The rational design of photocatalysts for CO 2 adsorption and activation is thus crucial. Here, we designed and synthesized two redox-active truxene-based conjugated microporous polymers linked by thiazolo [5,4-d]thiazole for metalfree photocatalytic reduction of CO 2 to CH 4 . Significantly, the optimized polymer with the extended π-conjugated system, denoted Tx-TzTz-CMP-2, presented a higher CH 4 production rate of 300.6 μmol g −1 h −1 with a selectivity of 71.2% without any metal cocatalyst and photosensitizer, which outperformed most of the previously reported photocatalysts. Experimental and theoretical investigations revealed that introducing phenyl as a π-bridge extending electron delocalization of conjugated system might effectively minimize exciton binding energy, thereby boosting the intramolecular charge transfer and separation abilities. Meanwhile, the N-site of the thiazole unit acted as an electron reservoir and a catalytic center for activating the adsorbed CO 2 and forming CH 4 by subsequent hydrogenation. This work highlights the significance of the extended π-conjugated system in metal-free conjugated microporous polymers to improve the activity and selectivity of CO 2 photoreduction to CH 4 .

Selective Integrating Molecular Catalytic Units into Bipyridine-Based Covalent Organic Frameworks for Specific Photocatalytic Fuel Production

“…TpBpy–Ir and TpBpy–Ru exhibited higher transient photocurrents and lower resistances compared to those of TpBpy, indicating their stronger ability for separating and transferring charges (Figure S15). , …”

Assessing the Impact of π‐Conjugation Length on Aggregation Induced Emission and Self‐Assembly Formation of α‐Cyanostilbene and Bis‐Cyanostilbene

“…According to these findings, as π‐conjugation increased, so did absorption and emission, resulting in a red shift. A review of the literature on organic chromophoric systems revealed that the more conjugated the π‐system, the longer the wavelength of photon captured [28,29] . The proven fact is that compounds having a sufficient number of conjugated bonds in their molecular core may absorb light photons in the visible area, resulting in compounds of yellow to red color.…”

“…A review of the literature on organic chromophoric systems revealed that the more conjugated the π-system, the longer the wavelength of photon captured. [28,29] The proven fact is that compounds having a sufficient number of conjugated bonds in their molecular core may absorb light photons in the visible area, resulting in compounds of yellow to red color. Figure 1c shows that αcyanostilbene CYS is a white compound in visible light and emits blue light when exposed to UV light irradiation (λ ex .…”

Facile synthesis of benzothiadiazole and its derivative-based covalent organic frameworks using “two-in-one” monomers for photocatalytic hydrogen generation

“…In the past few decades, covalent organic frameworks (COFs) 1–3 have received great attention for applications including but not limited to gas separation and storage, 4,5 catalysis 6,7 and sensing 8–11 due to their highly tunable structures and compositions. 12–15 The electronic structures of resultant COFs can readily be tuned by tailoring the organic building units, among which the photofunctional COFs exhibit a wide range of potential applications, such as photocatalytic carbon dioxide reduction, 16–19 hydrogen peroxide production 20–22 and hydrogen generation. 23,24…”