Exploring the “Goldilocks Zone” of Semiconducting Polymer Photocatalysts by Donor–Acceptor Interactions

Abstract

Water splitting using polymer photocatalysts is a key technology to a truly sustainable hydrogen-based energy economy. Synthetic chemists have intuitively tried to enhance photocatalytic activity by tuning the length of π-conjugated domains of their semiconducting polymers, but the increasing flexibility and hydrophobicity of ever-larger organic building blocks leads to adverse effects such as structural collapse and inaccessible catalytic sites. To reach the ideal optical band gap of about 2.3 eV, A library of eight sulfur and nitrogen containing porous polymers (SNPs) with similar geometries but with optical band gaps ranging from 2.07 to 2.60 eV was synthesized using Stille coupling. These polymers combine π-conjugated electron-withdrawing triazine (C N ) and electron donating, sulfur-containing moieties as covalently bonded donor-acceptor frameworks with permanent porosity. The remarkable optical properties of SNPs enable fluorescence on-off sensing of volatile organic compounds and illustrate intrinsic charge-transfer effects.

Molecular Heterostructures of Covalent Triazine Frameworks for Enhanced Photocatalytic Hydrogen Production

“…Importantly, properly hybridized CTF‐BT/Th exhibited much improved activities with a maximum value of 6.6 mmol g −1 h −1 observed for CTF‐BT/Th‐1: about 4–6 times greater than those of CTF‐BT and CTF‐Th. To our knowledge, such a large hydrogen‐production rate is remarkable, and our system significantly outperformed most conjugated‐polymer photocatalysts reported so far (see Table S2) …”

Reducing the Exciton Binding Energy of Donor–Acceptor‐Based Conjugated Polymers to Promote Charge‐Induced Reactions

“…[11] In this case,t he increase in the energy difference between the electron donor and the electron acceptor and the decrease in the energy loss of E CT is highly desirable,b ut achieving these properties in conjugated polymers still remains ac hallenge. [12] Minimization of the energy loss,which is mostly caused by overcoming the large E b , [13] is ap romising approach for increasing the rate of the charge migration process of the conjugated polymers.Agood example provided by photophysical studies is that am ore delocalized environment for charge migration in the CT state may facilitate adecrease in E b and thus enhance the charge transfer process. [14] This inspires us to reduce E b by modulating the charge transfer pathway,n amely,b yt ailoring the local donor-acceptor structure of the linear polymers.Amore efficient charge transfer will minimize the energy loss of E CT and thus create more electrons at the acceptor side,most likely promoting the resultant photoactivity.…”

Reducing the Exciton Binding Energy of Donor–Acceptor‐Based Conjugated Polymers to Promote Charge‐Induced Reactions

“…Otherwise, the excited charge will recombine into the ground state instantly . In this case, the increase in the energy difference between the electron donor and the electron acceptor and the decrease in the energy loss of E CT is highly desirable, but achieving these properties in conjugated polymers still remains a challenge …”