Oligoethylene Glycol Side Chains Increase Charge Generation in Organic Semiconductor Nanoparticles for Enhanced Photocatalytic Hydrogen Evolution

Abstract

Organic semiconductor nanoparticles (NPs) composed of an electron donor/acceptor (D/A) semiconductor blend have recently emerged as an efficient class of hydrogen‐evolution photocatalysts. It is demonstrated that using conjugated polymers functionalized with (oligo)ethylene glycol side chains in NP photocatalysts can greatly enhance their H2‐evolution efficiency compared to their nonglycolated analogues. The strategy is broadly applicable to a range of structurally diverse conjugated polymers. Transient spectroscopic studies show that glycolation facilitates charge generation even in the absence of a D/A heterojunction, and further suppresses both geminate and nongeminate charge recombination in D/A NPs. This results in a high yield of photogenerated charges with lifetimes long enough to efficiently drive ascorbic acid oxidation, which is correlated with greatly enhanced H2‐evolution rates in the glycolated NPs. Glycolation increases the relative permittivity of the semiconductors and facilitates water uptake. Together, these effects may increase the high‐frequency relative permittivity inside the NPs sufficiently, to cause the observed suppression of exciton and charge recombination responsible for the high photocatalytic activities of the glycolated NPs.

Preparation, characterization, evaluation and mechanistic study of organic polymer nano-photocatalysts for solar fuel production

“…Ultrafast exciton separation in pair with increased yield of long-lived photogenerated charges was observed by Kosco et al for glycolated PNP even without D-A heterojunction. 108 At the same time implementation of the heterojunction could further promote exciton dissociation for glycolated PNP. This work showed that hydrophilic glycol side chains enhance e r of the PNP environment, promoting water molecules to penetrate inside the PNP and reducing coulombic attraction between photogenerated electrons and holes.…”

“…This work showed that hydrophilic glycol side chains enhance e r of the PNP environment, promoting water molecules to penetrate inside the PNP and reducing coulombic attraction between photogenerated electrons and holes. 108…”

“…56 Recently, Kosco et al have shown that both geminate and nongeminate recombination can be efficiently slowed down from typically observed ps-ns timescales up to ms timescale by introduction of glycol side to the polymer backbone used for PNP preparation. 108…”

Covalent Networking of a Conjugated‐Polymer Photocatalyst to Promote Exciton Diffusion in the Aqueous Phase for Efficient Hydrogen Production

“…Additionally, Jan et al. [ 26 ] and Miaojie et al. [ 27 ] showed high hydrogen production by synthesizing polymers with tuned glycol side‐chain in the form of nanoparticles.…”

“…To solve these problems, Reiner et al [20] modified from alkyl to glycol side-chains and found that hydrophilic side-chains enhanced the lifetime of photogenerated polaronic states. Additionally, Jan et al [26] and Miaojie et al [27] showed high hydrogen production by synthesizing polymers with tuned glycol sidechain in the form of nanoparticles. Another possible solution is to combine the chemically robust crosslinked alkyl side-chains of CPs with small molecules, such as photo-crosslinkers, that restrain the swelling caused by residual organic solvents and reduce the free volume of CPs for efficient exciton diffusion and transfer.…”