There is increasing interest in harnessing sunlight to drive the synthesis of molecular fuels and chemicals, including in particular water photolysis to yield molecular oxygen and hydrogen. Whilst most research to date has focused on inorganic photoelectrodes and photocatalysts, there is now increasing interest in the use of organic semiconductors for sunlight to fuel applications. There has been substantial progress in recent years in the development of both photoelectrodes and photocatalysts based on organic semiconductors, motivated in particular by the energetic, spectral and morphological tunability of these materials. I will start my talk by introducing some of the recent progress in the use of organic semiconductors for solar to fuel applications. I will discuss the charge carrier lifetime challenge for solar to fuel applications, highlighting how this has parallels, but also differences, with organic solar cells.   I will then go on to discuss some of our recent studies employing transient optical spectroscopies measuring charge carrier dynamics in organic photoelectrodes and photocatalysts and how these impact upon the efficiency of solar driven fuel synthesis, covering a range of organic polymer and small molecule materials for both water and carbon dioxide reduction.

Organic semiconductors are increasingly recognised as promising materials for solar fuels photocatalysis due to their structural tunability, visible light absorption, and potential for low-energy synthesis. This talk will discuss recent advances in constructing organic donor–acceptor heterojunctions using micro and meso-porous materials. A particular focus will be on strategies to achieve efficient charge separation and transport through heterojunction formation, which can overcome intrinsic recombination losses common in single-component systems.

Conventional methods to form heterojunctions—such as nanoprecipitation or nanoemulsion—are typically restricted to organic semiconductors that are soluble in organic solvents. As a result, these methods are best suited to linear, “OPV-type” polymers that are non-porous. This limitation excludes many of the most promising photocatalysts, including insoluble 2D conjugated polymers and network materials that exhibit long-range order and porosity that can allow for efficient interaction of redox active reagents and active sites. In particular, hydrophilic microporosity—engineered via backbone design or post-polymerisation modification—plays a vital role in improving wettability and electrolyte accessibility, thus enhancing photocatalytic performance. The degree to which water integrates into organic semiconductor materials also significantly changes the kinetics of charge generation and lifetime.

We explore templated growth approaches that enable the controlled assembly of chemically distinct but topologically matched donor and acceptor polymers into coherent heterojunctions. This strategy allows for the integration of insoluble and rigid materials into defined interfacial architectures that promote ultrafast charge separation and suppress recombination. Templated donor–acceptor heterostructures show significantly enhanced hydrogen evolution activity compared to their individual components and are capable of generating long-lived charges under non-sacrificial conditions. The strategy provides a modular pathway to build efficient organic heterojunctions using materials traditionally excluded from conventional processing.

By bridging synthetic design, supramolecular assembly, and interface engineering, this approach opens up a new class of materials for heterojunction formation and present new possibilities for cocatalyst integration in light-driven hydrogen evolution and carbon dioxide reduction by organic semiconductors.

The bulk heterojunction (BHJ) concept, which has been successfully developed for solution-processed organic semiconductor-based photovoltaic (OPV) devices, offers a promising route to high-performance, scalable, and inexpensive photocatalyst nanoparticles (NPs) for solar-driven hydrogen production. However, state of the art BHJ NPs exhibit quantum yields far below OPVs, thus understanding how NPs characteristics affect their performance is a major goal. Herein we present insights to NP formation and co-catalyst deposition that demonstrate the effect of NP size and co-catalyst morphology on the performance of PTB7-Th:ITIC BHJ NPs. Specifically, using the emulsion NP preparation route, we report how BHJ NP size influences photocatalytic H₂ evolution, with a drastic increase in H₂ production when reducing NP diameter from 230 nm to 25 nm. Moreover, we introduce a halted photodeposition-dialysis method that affords unprecedented control over platinum (Pt) co-catalyst loading and morphology. Applying this method with typical Pt deposition conditions gave a max H₂ evolution rate of 140 mmol h⁻¹ g⁻¹ (based on semiconductor mass) with only 15.2 wt % Pt and suggested an optimum loading of < 20 wt % Pt, above which parasitic light absorption decreases the H₂ evolution rate.

Multiphoton excitation can enable near-infrared (NIR) activation of well-known
chromophores, but it requires high-power ultrashort-pulsed lasers and suffers from
drawbacks, such as photobleaching and short luminescence lifetimes. Long-lived
emissive probes are of great interest for photoluminescence imaging and NIR-to-
visible (Vis) molecular photon upconversion (UC).
Such probes can include transition metal complexes and organic compounds with
extended conjugation, capable of room-temperature phosphorescence, while organic
dyes can display delayed fluorescence, and lanthanide cations can be sensitized by
antenna chromophores. However, none of these systems exhibit UC behavior upon
NIR-excitation, an essential feature for practical photonic applications, such as
photocatalysis, bioimaging, and sensing.
Remarkably, high-nuclearity compounds constituted of rigid metal cores (lanthanides)
encapsulated by organic ligands, are emerging as the next generation of optical
materials.
We report here on the successful synthesis of a homometallic lanthanide (Yb) MCA,
including in its structure an organic chromophore covalently linked to ytterbium, and
determined its crystalline structure and their potential application in temperature
sensing.

The urgent need to decarbonize energy systems and to secure resilient, low-carbon energy carriers has driven intense interest in converting sunlight into chemical fuels. Photo(electro)chemical reduction of CO₂ and water to produce solar fuels is a particularly attractive pathwa. Despite significant advances, the field remains limited by intrinsic material challenges, insufficient light harvesting across the solar spectrum, rapid recombination of photogenerated charge carriers, poor selectivity toward desired products, and instability under operating conditions. Addressing these limitations requires a new generation of engineered photoactive materials and device architectures that combine strong light absorption, efficient charge separation and transport, abundant and well-defined catalytic sites, and robust chemical stability.

Organo–inorganic hybrid systems have emerged as a powerful strategy to meet these demands. By integrating inorganic semiconductors or metal nanoparticles with molecularly tunable organic frameworks and conjugated polymers, hybrids combine complementary strengths: the superior charge mobility and catalytic activity of inorganic components with the versatile light-absorption, chemical tunability and porosity of organic materials. In particular, organic semiconducting polymers, conjugated porous polymers (CPPs), covalent organic frameworks (COFs), and porous organic frameworks related to metal-organic frameworks (MOFs), play multifaceted roles in hybrid photocatalysts. When they are coupled to inorganic semiconductor or co-catalytic nanoparticles, collectively enhanced the production and allow to control the selectivity.

We report a systematic exploration of strategies to engineer organo–inorganic hybrid photo(electro)catalysts aimed at improving solar-fuel production. Approaches include the production of hybrid heterojunctions between inorganic semiconductors and conjugated polymers to spatially separate electrons and holes. These hybrid systems lead to substantial gains in quantum efficiency and product selectivity compared with bare inorganic or organic components, as the hybrid interfaces promote directional charge transfer and suppress non-productive recombination.

To elucidate the mechanistic origins of the observed performance improvements we combine operando and in-situ spectroscopies with computational modelling. Near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and operando FTIR track chemical speciation and surface intermediates during reaction, while transient absorption spectroscopy (TAS) quantifies charge-carrier dynamics and lifetimes. Theoretical calculations provide atomistic insight into adsorption geometries, reaction energetics and interfacial electronic structure. These complementary tools reveal that hybrid catalysts exhibit enhanced light absorption, accelerated interfacial charge transfer and the stabilization of key reaction intermediates relative to their single-component counterparts, factors that collectively rationalize improved activity and selectivity.

Providing global energy supply in a sustainable manner is one of the main challenges of our generation. We are therefore, in the urge to find alternative resources and materials. In this sense, organic materials are the best candidates to fabricate electronic devices since we can tailor their properties by molecular design. They have other advantages such as flexibility, light weight, portability and scalability. Still, the efficiency of organic devices is far from the one of inorganic materials or perovskites. Despite the progress made in the field, the race for achieving efficiency records, has hampered research focused on solving other fundamental issues, such as device morphology and charge recombination. In this talk, I will show different strategies to demonstrate how noncovalent interactions can enhance charge transport and device efficiency in organic electronic devices (Figure 1).^1,2 In our group we incorporate hydrogen bonds to extraordinarily small semiconductors to enhance charge carrier mobility and lifetime,^3,4 and introduce chiral centers to explore the Chiral Induced Spin Selectivity (CISS) effect to decrease charge recombination.⁵ The synthesis, self-assembly and optical properties will be shown and correlated to the charge transport results obtained by using electrodeless techniques and full devices. The spin selectivity results explored by scanning tunnel microscopy (STM) on spectroscopy mode (STS), show how it is possible to guide charge carriers through chiral supramolecular structures (Figure 1b).⁵ 

Photochemical solar energy conversion in molecular electronic materials used as photocatalysts follows an analogous pathway to photovoltaic energy conversion in organic solar cells. In both cases generation of a localized excited state by photon absorption is followed by exciton dissociation to generate a sequence of charge separated species. However, whilst photovoltaic energy conversion is now relatively efficient, photochemical energy conversion using polymer photocatalysts involves significant energy losses. We will use a common framework to analyse the behaviour and performance of photovoltaic and photochemical energy conversion systems based on organic semiconductors. We use experimental measurements and simulation to investigate how chemical structure and environment influence the energy conversion process in a variety of model materials systems. We will attempt to identify the factors limiting photochemical energy conversion in these sytems.