Developing highly efficient photocatalyts for water splitting is one of the grand challenges in solar energy conversion. Here, we report the rational design and synthesis of porous conjugated polymer (PCP) that photocatalytically generates hydrogen from water splitting. The design mimics natural photosynthetics systems with conjugated polymer component to harvest photons and the transition metal part to facilitate catalytic activities. A series of PCPs have been synthesized with different light harvesting chromophores and transition metal binding bipyridyl (bpy) sites. The photocatalytic activity of these bpy-containing PCPs can be greatly enhanced due to the improved light absorption, better wettability, local ordering structure, and the improved charge separation process. The PCP made of strong and fully conjugated donor chromophore DBD (M4) shows the highest hydrogen production rate at ∼33 μmol/h. The results indicate that copolymerization between a strong electron donor and weak electron acceptor into the same polymer chain is a useful strategy for developing efficient photocatalysts. This study also reveals that the residual palladium in the PCP networks plays a key role for the catalytic performance. The hydrogen generation activity of PCP photocatalyst can be further enhanced to 164 μmol/h with an apparent quantum yield of 1.8% at 350 nm by loading 2 wt % of extra platinum cocatalyst.
Developing
photocatalytic systems for water splitting to generate
oxygen and hydrogen is one of the biggest chemical challenges in solar
energy utilization. In this work, we report the first example of heterogeneous
photocatalysts for hydrogen evolution based on in-chain cobalt-chelating
conjugated polymers. Two conjugated polymers chelated with earth-abundant
cobalt ions were synthesized and found to evolve hydrogen photocatalytically
from water. These polymers are designed to combine functions of the
conjugated backbone as a light-harvesting antenna and electron-transfer
conduit with the in-chain bipyridyl-chelated transition metal centers
as catalytic active sites. In addition, these polymers are soluble
in organic solvents, enabling effective interactions with the substrates
as well as detailed characterization. We also found a polymer-dependent
optimal cobalt chelating concentration at which the highest photocatalytic
hydrogen production (PHP) activity can be achieved.
This work demonstrates edge-on chemical gating effect in molecular wires utilizing the pyridinoparacyclophane (PC) moiety as the gate. Different substituents with varied electronic demands are attached to the gate to simulate the effect of varying gating voltages similar to that in field-effect transistor (FET). It was observed that the orbital energy level and charge carrier's tunneling barriers can be tuned by changing the gating group from strong electron acceptors to strong electron donors. The single molecule conductance and current-voltage characteristics of this molecular system are truly similar to those expected for an actual single molecular transistor.
A new
series of donor–acceptor ladder-type molecules were
synthesized via Scholl reaction. These molecules contain up to 25-fused
rings but still show good air stability and good solubility. The ring-fusing
reaction is found to be sensitive to the nature of the side-chain
in donor units. The molecular conformations were investigated by 2D
NMR and DFT calculations. The photophysical properties were investigated
and an intense intramolecular charge-transfer was observed. All of
the molecules exhibit two-photon absorption (TPA) activity, and their
TPA cross-section shows a linear relationship with increasing conjugation
length of the thienoacene-PDI derivatives.
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