Authors: Yifan Bo
Source: OPUS FAU - Online publication system of Friedrich-Alexander-Universität Erlangen-Nürnberg (article, 2025-01-01)
Field: Materials Science — Materials Chemistry

Light Management and Solar Energy Conversion in Advanced Functional Materials Climate change and the depletion of fossil fuel resources are among the most serious challenges facing modern society, with significant environmental, economic, and social impacts. Continued reliance on fossil fuels not only accelerates greenhouse gas emissions but also threatens energy security due to increasingly limited reserves. To address these issues, sustainable energy sources can provide reliable, long-term solutions that are urgently needed. Among various renewable energy options, including wind, hydro, and biomass, solar energy is by far the most abundant and widely accessible. Efficient conversion of solar energy into usable power has become a pressing scientific and technological challenge. Solar energy can be converted into useful power mainly through two methods: photovoltaic conversion, which generates electricity, and photothermal conversion, which produces heat that can be utilized for various applications. This thesis aims to expand the fundamental understanding of light-matter interactions at the molecular level by exploring the photophysical properties of advanced functional materials. To achieve this, a wide range of spectroscopic techniques has been employed, including steady-state and time-resolved absorption and emission spectroscopy, as well as electrochemical measurements and spectroelectrochemistry. These methods allow for a detailed analysis of the electronic and photophysical processes that control material performance, contributing to the development of next-generation solar energy conversion systems. The research presented in this thesis is organized into three work packages. The first package involves the studies of singlet fission (SF) and triplet-triplet annihilation upconversion (TTA-UC) on several tetracene dimers. Initially, the complex interplay between the reverse process, intramolecular SF (intra-SF), and TTA-UC (intra-TTA-UC) is revealed by comparing two different tetracene dimers with meta-diethynylphenylene- and 1,3-diethynyladamantyl-linkers, which have different electronic couplings. The next study offers a strategy to achieve reversible SF using acid/base stimuli through functionalization of meta-diethynylphenylene-linked tetracene dimer with pyridyl end groups. Following this, a tetracene monomer functionalized with a pyridyl end group, acting as a ligand, is designed to form dimeric tetracene coordination complexes via self-assembly on platinum(II) or palladium(II) metal centers. The effects of the metal core on intra-SF and intra-TTA-UC are explored. Energy and electron transfer processes in multi-component architectures are discussed in the second work package. The first project systematically investigates the effects of oxygen on the photophysical properties of perylenediimide (PDI) derivatives. The oxygen-mediated sequential down-conversion, involving two steps of energy transfer between oxygen and the chromophore, is observed in PDI with appropriate singlet and triplet energy levels. In the second project, a series of electron donor-acceptor molecules based on spirofluorene is investigated to study the complex interplay between different excited-state decay pathways, including emission, charge transfer, charge separation, and intersystem crossing. For the third project, subphthalocyanine and 9-(4-N, N-dimethylaminophenyl)-ethynylanthryl units are combined to achieve panchromatic absorption in the visible region. Moreover, energy and electron transfer are observed to occur between them after excitation at anthryl units. Next, diketopyrrolopyrroles oligo‐grids with different sizes are investigated in the fourth project. On the ground state, oligo‐grids exhibit null-aggregation behaviors. In contrast, symmetry-breaking charge-separation is observed in these oligo‐grids in polar solvents after photoexcitation. The research in the third package focuses on photothermal conversion in transition metal phosphorus trichalcogenide-based materials (MPCh3). In the first project, nickel phosphorus trisulfide nanosheet-based converters are successfully fabricated and further utilized for photothermal conversion and desalination. Notably, this is the first report of MPCh3 materials for photothermal water evaporation and desalination. In the second project, light management on 2D/0D nano-heterojunctions by functionalizing iron phosphorus trisulfide nanosheets with carbon nanodots is explored, and an evaporator based on the nano-heterojunctions is used for photothermal conversion and solar desalination. Fossil fuel ; Renewable energy ; Solar energy ; Photovoltaic system ; Energy transformation ; USable ; Photovoltaics ; Photon upconversion ; Solar fuel Luminescence and Fluorescent Materials ; Chemical and Physical Properties of Materials ; SAS software applications and methods