Quantitative risk analysis for road tunnels complying with EU regulations

Tunnels have improved the connection of regions within the European Commission (EC) and have been used lately as a catalyst for economic development of previously isolated regions. However, the increasing number of these important infrastructures is raising upfront an endogenous problem, which is the severity of accidents that may occur. These risks have much greater impact when heavy goods vehicles (HGVs) or dangerous goods (DGs) are involved in the accident. As a result, the EC launched the EC Directive 2004/54/EC. In order to achieve a minimum acceptable level of safety, the EC Directive 2004/54/EC suggests, apart from the measures imposed based on tunnel characteristics, the implementation of a risk analysis in cases such as the opening of the road tunnel to DGs. The most widely accepted method for such quantitative risk analysis (QRA) is the OECD/PIARC QRA Model. This research exploits the QRA Model to perform a QRA for five illustrative cases in order to explore the sufficiency of the minimum tunnel safety measures imposed by the Directive when transportation of HGVs and DGs is allowed through the tunnel. The research concludes that, at least for tunnels with marginal values of the EC Directive classes for length and traffic, the risk exposure (F/N curves) lays over the acceptable safety limits of ALARP (as low as reasonably practicable) models. Thus, the manager of the tunnel should take seriously into account the provision of the Directive for further risk analysis and consider more safety measures as well as take into account the risk associated with the alternative routes

Erschließung Neuer Prinzipien der Singulettspaltung: Charakterisierung, Optimierung, und Identifikation von Neuartigen Materialien für die Singulettspaltung

Humankind undeniably has left its marks on the planet. The ever-growing world population necessitates the demand for more living space, food resources, and energy. These demands all in all lead to a deterioration of the global environment and climate, thus highlighting the overall negative impact humankind has on earth. Over the last years the outcry of society, especially from the younger generations, steadily grew, demanding from politicians around the world to fulfill the promises on working towards a sustainable, environmental friendly, and climate neutral energy production, in order to counter global warming and decrease the toll we create on the planet. The arguable best alternatives are renewable energies, with solar energy conversion through photovoltaic cells exhibiting the largest potential. However, single junction solar cells are starting to reach their maximum possible thermodynamic efficiency (SHOCKLEY QUEISSER limit) of about 33.7%. Therefore, new and innovative concepts are pivotal to elevate the efficiency of solar cells beyond their present limit. They furthermore need to be affordable and scalable to an industrial level to compete with currently fossil fuel based forms of energy generation. One concept is given by singlet fission (SF). It evolves around the down conversion of a singlet excited state (S1) into two triplet excited states (T1), resulting in multiple exciton generation (MEG). By implementing SF chromophores into the solar cells and exploiting MEG, it is theoretical possible to go beyond the SHOCKLEY QUEISSER limit. To achieve this goal, it is imperative to obtain a profound understanding on the fundamentals of SF. Numerous scientists dedicate their research towards the investigation of SF chromophores and the elucidation of its mechanism. The present thesis describes my input to this overarching area of investigation. To this end, this thesis provides a brief summary on the photophysical fundamentals, the most current insights into SF and its relevant intricacies. Moreover, a report on the widely-used SF chromophores gives the reader the necessary insight to achieve a general understanding of this topic and, by extension, of my research. My research, in particular, encompassed three main parts, namely the characterization of pentacene derived SF chromophores, the optimization of their SF efficiencies, and the identification of novel and superior SF chromophores beyond pentacene. The investigations were performed by applying a wide range of photophysical techniques including steady-state absorption and fluorescence, time correlated single photon counting (TCSPC), time-resolved transient absorption (TA), time-resolved infra-red (fsIR), and time-resolved electron paramagnetic resonance (TrEPR) spectroscopy. In addition, electrochemical and spectroelectrochemical (SEC) measurements further assisted in the investigations. Elaborating on the individual parts, the first one focused on the characterization of pentacene dimers, utilizing a variety of linkers and exploring the different electronic coupling regimes as they impact the SF mechanism and efficiency. The bulk of this thesis was dedicated to this part. In the first project, cross conjugation was chosen to ensure strong electronic through-bond coupling, resulting in intramolecular SF and triplet quantum yields (TQYs) as high as 162%. This study highlighted the importance of the solvent polarity and, thus, significance of the charge transfer (CT) state as part of SF, serving as an intermediator to the singlet correlated triplet pair state 1(T1T1). 1(T1T1) did not yield any uncorrelated triplet excited states (T1+T1) and exclusively decayed back to the ground state (S0S0) via triplet-triplet annihilation (TTA). This, again, showcased the strong electronic coupling between the pentacene moieties due to the selected binding motif. The second project went the opposite direction. By breaking the conjugation between the pentacenes via non-conjugated spacers, the weak coupling regime was scrutinized. This purely led to through-space interactions, upon which their ramifications on SF were explored. The utilization of flexible, alkyl derived spacers added a certain flexibility to the system. Only a gauche conformer allowed for sufficient interpentacene through space interactions. The damping in electronic coupling not only led to the additional population of a quintet correlated triplet pair 5(T1T1), but also allowed for its separation into free triplets (T1+T1). The investigated chromophores also highlighted the fine balance between exhibiting strong coupling and, thus, yielding high TQYs at the expense of separating into the (T1+T1), and weak coupling trading off high amounts of (T1+T1) with low TQYs. After dedicating a respective project to the strong and weak coupling regimes, the goal of the third project was to go beyond the classical description of coupling regimes. This was achieved by inserting platinum into the linker and investigate the ensuing impact of the internal heavy-atom effect on the SF mechanism. Platinum led to a unique perturbation of the ground, singlet, and triplet excited state potential energy surfaces and influenced the spin dynamics of SF. The fast and efficient SF led to a strong population of 1(T1T1), which subsequently, by virtue of the induced spin-orbit coupling of platinum, parallel transitioned into 3(T1T1) and 5(T1T1). These states ultimately led to a major population of (T1S0) in the former case, and a minor population of (T1+T1) in the latter case. The fourth project was a direct follow-up and involved the modification of the bridge by including chiral substituents and obtaining enantiomerically pure platinum dimers. This study featured the first investigations on the possible effects of chirality on the SF dynamics. However, the observed mechanism and yields were rather similar to the achiral counterpart. Only minor differences in rate constant and yields were observed, ultimately exposing the small impact chirality imparts upon the overall system. The second part involved the optimization of an already established SF chromophore. The optimization was realized by covalently connecting an energy donor, with complementary absorptions, to the linker of the pentacene dimer. This introduced panchromatic light harvesting to the SF chromophore. Following this design concept, the fifth project dealt with the optimization of an already published phenylene linked pentacene dimer (Pnc2) by applying zinc porphyrazine (ZnPz) based energy donors. The conjugates featured an efficient and unidirectional FÖRSTER RESONANCE ENERGY TRANSFER (FRET) from ZnPz to Pnc2, which subsequently underwent SF. This concept led to two follow-up projects, in which the first one replaced zinc porphyrazine with subporphyrazine as energy donor, as part of the sixth project. The goal was to expand the variety of applicable energy donors in the context of SF optimization. Subporphyrazine resulted in an improved panchromatic light harvesting, due to its broader and more intense absorptions in the 400 to 600 nm range, usually devoid of strong pentacene dimer related absorptions. It also introduced another layer of control regarding FRET, owing to its solvent polarity dependent fluorescence. The fluorescence of subporphyrazine was found to blue-shift after increasing the solvent polarity. This changed the spectral overlap between donor fluorescence and acceptor absorption, ultimately impacting the efficiency of FRET. The second follow-up and overall seventh project utilized subphthalocyanines as an energy donor and more specifically explored the role and nature of the molecular spacer on the intramolecular FRET. This was realized by controlling the distance between energy donor and acceptor, through the number of aryl units in between, and its flexibility, introduced via a CH2 group. Overall increasing the distance negatively impacted FRET. Introducing flexibility to the system circumvented the negative impact, as it brought the two interacting moieties closer together. Notably, the inclusion of aryl rings into the spacer negatively impacted intramolecular SF. The quinone-like conjugation led to an additional acceptor orbital, which was delocalized over both pentacenes and the bridging phenyl. This, in turn, disrupted the interactions between the pentacenes and restrained SF. The goal of the third part was to identify novel and modified SF chromophores, going beyond their pentacene derived counterparts and featuring superior properties. One such type of chromophore was explored in the eighth project with a nitrogen doped hexacene and two added off-linear benzene rings. The inserted nitrogens induced a weak decoupling resulting in a unique electronic structure and compartmentalized the acene backbone into a pyrene and an aza-tetracene part. These chromophores offered a superior stability and expanded the range of absorption compared to pentacenes. In terms of coupling strength, these chromophores are placed in the medium coupling regime, featuring a good balance between efficient SF and 1(T1T1) TQYs, while still allowing decoupling into (T1+T1). As a direct follow-up, the ninth project combined the ortho-dibenzodiazahexacene dimer from the previous study together with carbon nanotubes. The superior stability of dibenzodiazahexacene compared to pentacenes certainly stood out. In contrast to pentacene, they were able to sustain the required sonication during hybrid preparation. The carbon nanotubes served as an energy sink, which still allowed the initial SF, while collecting energy through an unidirectional energy transfer from the various SF related species during the process. This resulted altogether in an energy transfer efficiency beyond 100%. Another known class of SF chromophores includes the family of rylenes, upon which a perylene-monoimide dimer was investigated in greater detail as the tenth project. The perylene-monoimide dimer revealed to be subject to a geminate triplet-triplet annihilation up conversion (TTA-UC) channel at room temperature. This competed with the disentanglement of the formed correlated triplet pair from SF. Furthermore, the strong involvement of an intermediate CT state manifested itself by imposing a CT character onto the singlet (S1S0)CT and triplet 1(T1T1)CT excited states. Either lowering the temperature or increasing the solvent polarity suppressed TTA UC and stabilized 1(T1T1)CT. This highlighted the fine intricacies of adjusting couplings and thereupon manipulating the fate of the correlated triplet pair within SF. Diketopyrrolopyrroles are yet another class of SF chromophores and were picked up in the eleventh project. The utilization of a dithienylphenylene spacer and led to the construction of an ortho-, meta-, and para-regioisomer. This study highlighted the deep interconnectivity and participation of a CT state and its impact on SF in DPPs. Only a polar solvent allowed the population of 1(T1T1) and (T1+T1) by stabilizing the intermediate (S1S0)CT. But, the para-dimer also revealed that too strong of a stabilization and spatial separation of the diketopyrrolopyrroles can lead to a trap state and prevent SF from occurring by undergoing a symmetry breaking charge separation. This emphasized the fine balance when a CT state is involved as the extent of stabilization either mediates or blocks intramolecular SF in diketopyrrolopyrroles-based dimers. Besides the three parts, additional supplementary studies on a set of DPP monomers were performed in the twelfth project. This study aimed at obtaining a fundamental understanding on the photophysical behavior of DPPs and was not focused on SF. The measurements revealed a strong involvement of CT states during the excited state decay of DPPs, valuable knowledge explored in the abovementioned study. The accumulated knowledge of SF during my research additionally led to the creation of a review article. The main goal of the article was to provide the essential tools and knowledge required for studies based on SF energy conversion devices and pave the way towards their realization. In particular, the review article included a summary on the fundamental processes of inter- and intramolecular SF, gave an overview on the essential parameters of solar cells and the first achievements implementing SF into their device architecture. Most importantly it contained a collection of the most prevalent SF chromophores, with a listing of their photophysical and electrochemical properties, as found in the literature on their respective publications. These are crucial for choosing the appropriate dye and designing the respective solar cell. In essence, the three main parts presented in this thesis aimed at achieving a similar conclusion.Es ist unbestreitbar, dass die Menschheit ihre Spuren auf dem Planeten hinterlassen hat. Die stetig wachsende Weltbevölkerung erfordert mehr Wohnraum, Lebensmittel, und Energie. Diese Forderungen führen zu einer Verschlechterung der globalen Umwelt und des Klimas, was wiederum den negativen Einfluss der Menschheit auf die Erde unterstreicht. In den letzten Jahren wuchs der Aufschrei der Gesellschaft, insbesondere der jüngeren Generationen, stetig und forderten von Politikern weltweit die Versprechen zu erfüllen, entgegen einer nachhaltigen, umweltfreundlichen, und klimaneutralen Energieerzeug hinzuarbeiten um der globalen Erwärmung und dem Schaden, den wir auf den Planeten verursachen, entgegenzuwirken. Die wohl besten Alternativen sind erneuerbare Energien, wobei die Umwandlung von Sonnenenergie durch Photovoltaikzellen das größte Potenzial aufweist. Solarzellen mit einem p-n Übergang beginnen jedoch ihren maximal möglichen thermodynamischen Wirkungsgrad (SHOCKLEY QUEISSER Limit) von etwa 33.7% zu erreichen. Daher sind neue und innovative Konzepte von entscheidender Bedeutung, um den Wirkungsgrad von Solarzellen über ihre derzeitige Grenze hinaus zu steigern. Sie müssen außerdem erschwinglich und auf industrieller Ebene skalierbar sein, um mit den derzeit auf fossilen Brennstoffen basierenden Formen der Energieerzeugung konkurrieren zu können. Ein Konzept ist der Prozess der Singulett Spaltung (engl.: singlet fission, SF). Es dreht um die Abwärtsumwandlung eines angeregten Singulettzustandes (S1) in zwei angeregte Triplettzustände (T1), was zur Erzeugung mehrerer Exzitonen (engl.: multiple exciton generation, MEG) führt. Durch die Implementierung von SF Chromophoren in die Solarzellen und die Nutzung von MEG ist es theoretisch möglich, das SHOCKLEY QUEISSER Limit zu überschreiten. Um dieses Ziel zu erreichen, ist es unerlässlich, ein tiefgreifendes Verständnis der Grundlagen von SF zu erlangen. Zahlreiche Wissenschaftler widmen ihre Forschung der Untersuchung von SF Chromophoren und der Aufklärung ihres Mechanismus. Die vorliegende Arbeit beschreibt meinen Beitrag zu diesem übergreifenden Forschungsgebiet. Zu diesem Zweck bietet diese Arbeit eine kurze Zusammenfassung der photophysikalischen Grundlagen, der aktuellsten Einblicke in SF und seiner relevanten Feinheiten. Darüber hinaus gibt eine Auflistung über die weit verbreiteten SF Chromophore dem Leser den notwendigen Einblick, um ein allgemeines Verständnis über dieses Themas und damit meiner Forschung zu erlangen. Meine Forschung umfasste insbesondere drei Hauptteile, nämlich die Charakterisierung von Pentacen abgeleiteten SF Chromophoren, die Optimierung ihrer SF Effizienz und die Identifizierung neuer und überlegener SF-Chromophore jenseits von Pentacen. Die Untersuchungen wurden durchgeführt, indem eine breite Palette von photophysikalischen Techniken angewendet wurden, einschließlich stationärer Absorption und Fluoreszenz, zeitkorrelierter Einzelphotonenzählung (TCSPC), zeitaufgelöster transienter Absorption (TA), zeitaufgelöstem Infrarot (fsIR) und zeitaufgelöste elektronenparamagnetische Resonanz (TrEPR) Spektroskopie. Darüber hinaus unterstützten elektrochemische und spektroelektrochemische Messungen die Untersuchungen. Um etwas genauer auf die einzelnen Teile einzugehen, der erste konzentrierte sich auf die Charakterisierung von Pentacendimeren, unter Verwendung einer Vielzahl von Brücken, und die Untersuchung der verschiedenen elektronischen Kopplungsstärken und deren Einfluss auf den SF Mechanismus und die Effizienz. Der Großteil dieser Arbeit war diesem Teil gewidmet. Im ersten Projekt wurde die Kreuzkonjugation ausgewählt, um eine starke elektronische Kopplung über die chemische Bindung sicherzustellen, was zu intramolekularen SF und Triplettquantenausbeuten (TQYs) von bis zu 162% führte. Diese Studie hob die Bedeutung der Lösungsmittelpolarität und damit die Bedeutung des Ladungstransfers (engl.: charge transfer, CT) als Teil von SF hervor, der als Vermittler für den Singulett korrelierten Triplettpaarzustandes 1(T1T1) diente. 1(T1T1) ergab keine unkorreliertem Triplettzustand (T1+T1) und fiel ausschließlich über Triplett-Triplett Auslöschung (engl.: triplet-triplet annihilation, TTA) in den Grundzustand (S0S0) zurück. Dies zeigte erneut die starke elektronische Kopplung zwischen den Pentacen Einheiten aufgrund des ausgewählten Bindungsmotivs. Das zweite Projekt ging in die entgegengesetzte Richtung. Durch Aufbrechen der Konjugation zwischen den Pentacenen über nicht konjugierte Brücken wurde das schwache Kopplungsregime untersucht. Dies führte lediglich zu Wechselwirkungen über den Raum hinweg, bei denen ihre Auswirkungen auf SF untersucht wurden. Die Verwendung von Alkyl abgeleiteten Brücken fügte dem System eine gewisse Flexibilität hinzu. Nur ein Gauche-Konformation erlaubte ausreichende Wechselwirkung zwischen den Pentacenen über den Raum hinweg. Die Verringerung der elektronischen Kopplung führte nicht nur zur zusätzlichen Population eines Quintett korrelierten Triplett Paares 5(T1T1), sondern ermöglichte auch dessen Trennung in freie Tripletts (T1+T1). Die untersuchten Chromophore hoben auch das feine Gleichgewicht zwischen einer starken Kopplung und damit hohen TQYs auf Kosten der Trennung in (T1+T1) und einer schwachen Kopplung hervor, die hohe Mengen von (T1+T1) mit niedrigen TQYs eintauscht. Nachdem ein entsprechendes Projekt den starken und schwachen Kopplungsregimen gewidmet worden war, bestand das Ziel des dritten Projekts darin, über die klassische Beschreibung der Kopplungsregime hinauszugehen. Dies wurde erreicht, indem Platin in die Brücke eingefügt und der daraus resultierende Einfluss des internen Schweratomeffekts auf den SF Mechanismus untersucht wurde. Platin führte zu einer einzigartigen Störung der potenziellen Energieoberflächen des Grund, Singulett und Triplett angeregten Zustands und beeinflusste die Spin-Dynamik von SF. Schnelles und effizientes SF führte zu einer starken Population von 1(T1T1), welcher anschließend aufgrund der induzierten Spin Bahn-Kopplung durch Platin parallel in 3(T1T1) und 5(T1T1) überging. Dies Zustände führten letztendlich zu einer Hauptbevölkerung von (T1S0) im ersteren Fall und einer Nebenbevölkerung von (T1+T1) im letzteren Fall. Das vierte Projekt war ein direkter Nachfolger und umfasste die Modifikation der Brücke durch Einbeziehung chiraler Substituenten und den Erhalt von enantiomerenreiner Platindimere. Diese Studie enthielt die ersten Untersuchungen zu den möglichen Auswirkungen der Chiralität auf die SF Dynamik. Der beobachtete Mechanismus und die Ausbeute waren jedoch dem achiralen Gegenstück ziemlich ähnlich. Es wurden nur geringfügige Unterschiede in der Geschwindigkeitskonstante und TQYs beobachtet, wodurch letztendlich die geringe Auswirkung der Chiralität auf das Gesamtsystem sichtbar wurde. Der zweite Teil betraf die Optimierung eines bereits etablierten SF Chromophors. Die Optimierung wurde durch kovalent Verbindung eines Energiedonors mit komplementären Absorptionen mit dem Linker des Pentacendimers realisiert. Dies führte zu einer panchromatischen Lichtabsorption des SF Chromophors. Nach diesem Konzept befasste sich das fünfte Projekt mit der Optimierung eines bereits veröffentlichten Phenyl verbrückten Pentacendimers (Pnc2), durch Anwendung von Eniergiedonoren auf Basis von Zinkporphyrazin (ZnPz). Die Konjugate zeigten einen effizienten und unidirektionalen Förster-Resonanzenergietransfer (engl.: FÖRSTER RESONANCE ENERGY TRANSFER, FRET) von ZnPz nach Pnc2, dem anschließend SF folgte. Dieses Konzept führte zu zwei Folgeprojekten, bei denen das erste im Rahmen des sechsten Projekts Zinkporphyrazin durch ein Subporphyrazin als Energiedonor ersetzte. Ziel war es, die Vielfalt der anwendbaren Energiedonoren im Rahmen der SF Optimierung zu erweitern. Subporphyrazin führte zu einer verbesserten panchromatischen Lichtabsorption aufgrund seiner breiteren und intensiveren Absorptionen im Bereich von 400 bis 600 nm, welcher normalerweise keine starken Absorptionen im Zusammenhang mit Pentacendimeren aufweist. Aufgrund seiner von der Lösungsmittelpolarität abhängigen Fluoreszenz wurde auch ein weiteres Kontrollelement in Bezug auf FRET eingeführt. Es wurde festgestellt, dass sich die Fluoreszenz von Subporphyrazin durch Erhöhung der Lösungsmittelpolarität blau verschiebt. Dies veränderte die spektrale Überlappung zwischen Donorfluoreszenz und Akzeptorabsorption und beeinflusste letztendlich die Effizienz von FRET. Das zweite Folge- und siebte Gesamtprojekt verwendete Subphthalocyanine als Energiedonor und untersuchte insbesondere die Rolle und Natur der molekularen Brücke auf den intramolekularen FRET. Dies wurde realisiert, indem der Abstand zwischen Energiedonor und Energieakzeptor durch die Anzahl der dazwischen liegenden Aryleinheiten und seine über eine CH2-Gruppe eingeführte Flexibilität gesteuert wurden. Insgesamt wirkte sich eine größere Entfernung negativ auf den FRET aus. Durch die Einführung von Flexibilität in

A Flail Tricuspid Valve

A 30-year-old man was admitted to the hospital because of palpitations. He had a life-threatening liver rupture five years earlier, after a massive uncontrolled explosion of a big bunch of fireworks. Transthoracic echocardiography revealed severe tricuspid regurgitation due to a flail anterior leaflet of the tricuspid valve. Transesophageal echocardiography had an additive imaging value in demonstrating additionally a flail posterior leaflet. Flail tricuspid valve causing severe regurgitation is usually due to mechanical trauma. Since it is well tolerated for years, the diagnosis may be delayed or missed entirely. Echocardiography has allowed easier diagnosis of this condition resulting in earlier and, hence, more effective treatment

Förster Resonance Energy Transfer Sensitized Singlet Fission in BODIPY-Pentacene Dimer Conjugates

In the present work, the energy donor 4,4-difluoro-4-bora-3a,4a-diaza-sindacene (BODIPY) is used for the first time in combination with a pentacene dimer (Pnc2) to provide the conjugate BODIPYPnc2 that features absorption throughout a large part of the solar spectrum. Upon photoexcitation, the singlet excited state energy of BODIPY is transferred to the pentacene dimer via intramolecular Förster resonance energy transfer (FRET). Subsequently, the pentacene dimer undergoes intramolecular singlet fission. In this process, a singlet correlated triplet pair is generated from the first singlet excited state via coupling to an intermediate state. The results show that solvent polarity has an influence on the system, with the largest FRET rate (i.e., 7.46 × 1011 s−1) being obtained in the most polar solvent (namely, benzonitrile) along with the largest triplet quantum yield (i.e., 207 ± 20%)A.-S.W., G.L., and I.P. contributed equally to this work. D.M.G. thanks the financial support from ″the German Research Foundation (DFG) via SFB 953 “Synthetic Carbon Allotropes” and “Solar Technologies go Hybrid (SolTech)” Initiative of the Bavarian Ministry for Science. T.T. acknowledges financial support from MICINN (PID2020-116490GB-I00 and TED2021-131255B-C43), the Comunidad de Madrid and the Spanish State through the Recovery, Transformation and Resilience Plan [“Materiales Disruptivos Bidimensionales (2D)” (MAD2D-CM) (UAM1)-MRR Materiales Avanzados], and the European Union through the Next Generation EU funds. IMDEA Nanociencia acknowledges support from the “Severo Ochoa” Programme for Centres of Excellence in R&D (MINECO, Grant SEV2016-0686). R.R.T. acknowledges funding from the Natural Sciences and Engineering Research Council of Canada (NSERC, grant no. RGPIN-2017-05052) and the Canada Foundation for Innovation (CFI

Optimisation and investment analysis of two biomass-to-heat supply chain structures

As oil prices have risen dramatically lately, many people explore alternative ways of heating their residences and businesses in order to reduce the respective cost. One of the options usually considered nowadays is biomass, especially in rural areas with significant local biomass availability. This work focuses on comparing two different biomass energy exploitation systems, aiming to provide heat to a specific number of customers at a specific cost. The first system explored is producing pellets from biomass and distributing them to the final customers for use in domestic pellet boilers. The second option is building a centralised co-generation (CHP) unit that will generate electricity and heat. Electricity will be fed to the grid, whereas heat will be distributed to the customers via a district heating network. The biomass source examined is agricultural residues and the model is applied to a case study region in Greece. The analysis is performed from the viewpoint of the potential investor. Several design characteristics of both systems are optimised. In both cases the whole biomass-to-energy supply chain is modelled, both upstream and downstream of the pelleting/CHP units. The results of the case study show that both options have positive financial yield, with the pelleting plant having higher yield. However, the sensitivity analysis reveals that the pelleting plant yield is much more sensitive than that of the CHP plant, therefore constituting a riskier investment. The model presented may be used as a decision support system for potential investors willing to engage in the biomass energy field

Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers

We show unambiguous and compelling evidence by means of pump–probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 ± 10% and (0.7 ± 0.1) × 1012 s−1, respectively, in room temperature solutions

Singlet Fission in Pyrene‐Fused Azaacene Dimers

Singlet fission has emerged as a promising strategy to avoid the loss of extra energy through thermalization in solar cells. A family of dimers consisting of nitrogen‐doped pyrene‐fused acenes that undergo singlet fission with triplet quantum yields as high as 125 % are presented. They provide new perspectives for nitrogenated polycyclic aromatic hydrocarbons and for the design of new materials for singlet fission

Intramolecular Triplet Diffusion Facilitates Triplet Dissociation in a Pentacene Hexamer

Triplet dynamics in singlet fission depend strongly on the strength of the electronic coupling. Covalent systems in solution offer precise control over such couplings. Nonetheless, efficient free triplet generation remains elusive in most systems, as the intermediate triplet pair 1(T1T1) is prone to triplet‐triplet annihilation due to its spatial confinement. In the solid state, entropically driven triplet diffusion assists in the spatial separation of triplets, resulting in higher yields of free triplets. Control over electronic coupling in the solid state is, however, challenging given its sensitivity to molecular packing. We have thus developed a hexameric system (HexPnc) to enable solid‐state‐like triplet diffusion at the molecular scale. This system is realized by covalently tethering three pentacene dimers to a central subphthalocyanine scaffold. Transient absorption spectroscopy, complemented by theoretical structural optimizations and steady‐state spectroscopy, reveals that triplet diffusion is indeed facilitated due to intramolecular cluster formation. The yield of free triplets in HexPnc is increased by a factor of up to 14 compared to the corresponding dimeric reference (DiPnc). Thus, HexPnc establishes crucial design aspects for achieving efficient triplet dissociation in strongly coupled systems by providing avenues for diffusive separation of 1(T1T1), while, concomitantly, retaining strong interchromophore coupling which preserves rapid formation of 1(T1T1).Efficient free triplet generation via singlet fission remains elusive in covalent systems. We have developed a hexameric pentacene system, in which three pentacene dimers are covalently linked to a central subphthalocyanine scaffold. This allows for an entropically driven triplet diffusion, resulting in higher yields of free triplets, and establishes crucial design aspects for achieving efficient triplet dissociation in strongly coupled systems. image Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165