Conjugated Porous Polymers Based on BODIPY and BOPHY Dyes in Hybrid Heterojunctions for Artificial Photosynthesis

Developing highly efficient photocatalysts for artificial photosynthesis is one of
the grand challenges in solar energy conversion. Among advanced photoactive
materials, conjugated porous polymers (CPPs) possess a powerful combination of
high surface areas, intrinsic porosity, cross-linked nature, and fully π-conjugated
electronic systems. Here, based on these fascinating properties, organic–inorganic
hybrid heterostructures composed of CPPs and TiO2 for the photocatalytic
CO2 reduction and H2 evolution from water are developed. The study is focused
on CPPs based on the boron dipyrromethene (BODIPY) and boron pyrrol hydrazine
(BOPHY) families of compounds. It is shown that hybrid photocatalysts are
active for the conversion of CO2 mainly into CH4 and CO, with CH4 production
4 times over the benchmark TiO2. Hydrogen evolution from water surpassed
by 37.9-times that of TiO2, reaching 200 mmol gcat
−1 and photonic efficiency
of 20.4% in the presence of Pt co-catalyst (1 wt% Pt). Advanced photophysical
studies, based on time-resolved photoluminescence and transient absorption
spectroscopy, reveal the creation of a type II heterojunction in the hybrids. The
unique interfacial interaction between CPPs and TiO2 results in longer carriers’
lifetimes and a higher driving force for electron transfer, opening the door to a
new generation of photocatalysts for artificial photosynthesis.