Project description:Efficient syntheses that incorporate thiophene units into different extended conjugation systems are of interest as a result of the prevalence of sulfur-rich aromatics in organic electronics. Self-organization by using liquid crystal properties is also desirable for optimal processing of organic electronics and optical devices. In this article, we describe a two-step process to access extended regioisomers of polyaromatics with different shapes. This method involves an efficient single or double benzannulation from an alkyne precursor followed by Scholl cyclization. In spite of their unconventional nondiscoid shape, these materials display stable columnar liquid crystal phases. We examine the photophysical and electrochemical properties and find that structurally very similar thiophene-fused polyaromatics display significant differences in their properties.
Project description:The triplet pair is the key functional unit in triplet-triplet annihilation photon upconversion. The same molecular properties that stabilize the triplet pair also allow dimers to form on the singlet energy surface, creating an unwanted energy relaxation pathway. Here we show that excimer formation most likely is a consequence of a triplet dimer formed before the annihilation event. Polarity-dependent studies were performed to elucidate how to promote wanted emission pathways over excimer formation. Furthermore, we show that the yield of triplet-triplet annihilation is increased in higher-viscosity solvents. The results will bring new insights in how to increase the upconversion efficiency and how to avoid energy-loss channels.
Project description:Diffusion controlled chemical reactions are usually observed in three dimensional media. In contrast, planar bimolecular reactions taking place between reagents adsorbed at a soft interface are two-dimensional and therefore cannot be studied within the same formalism. Indeed, soft interfaces allow the adsorbed species to freely diffuse in a liquid-like manner. Here, we present the first experimental observation of a diffusion-controlled reaction in an environment that is planar at the ångström scale. By means of time-resolved surface second harmonic generation, an inherently surface sensitive technique, we observed that the kinetics of the diffusion of the reagents in the plane decreases as the surface concentration of adsorbed species increases. This is of course not the case for bulk reactions where the rates always increase with the reactant concentration. Such changes in the kinetics regime were rationalised as the evolution from a regular 2D free diffusion regime to a geometry-controlled scheme.
Project description:Understanding the temperature dependency of triplet-triplet annihilation upconversion (TTA-UC) is important for optimizing biological applications of upconversion. Here the temperature dependency of red-to-blue TTA-UC is reported in a variety of neutral PEGylated phospholipid liposomes. In these systems a delicate balance between lateral diffusion rate of the dyes, annihilator aggregation, and sensitizer self-quenching leads to a volcano plot, with the maximum upconversion intensity occurring near the main order-disorder transition temperature of the lipid membrane.
Project description:Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy separations; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.
Project description:Photon upconversion has enjoyed increased interest in the last years due to its high potential for solar-energy harvesting and bioimaging. A challenge for triplet-triplet annihilation upconversion (TTA-UC) processes is to realize these features in solid materials without undesired phase segregation and detrimental dye aggregation. To achieve this, we combine a palladium porphyrin sensitizer and a 9,10-diphenylanthracene annihilator within a crystalline mesoporous metal-organic framework using an inverted design. In this modular TTA system, the framework walls constitute the fixed sensitizer, while caprylic acid coats the channels providing a solventlike environment for the mobile annihilator in the channels. The resulting solid material shows green-to-blue delayed upconverted emission with a luminescence lifetime of 373±5??s, a threshold value of 329?mW?cm-2 and a triplet-triplet energy transfer efficiency of 82?%. The versatile design allows straightforward changing of the acceptor amount and type.
Project description:In the strive to develop triplet-triplet annihilation photon upconversion (TTA-UC) to become applicable in a viable technology, there is a need to develop upconversion systems that can function well in solid states. One method to achieve efficient solid-state TTA-UC systems is to replace the intermolecular energy-transfer steps with the corresponding intramolecular transfers, thereby minimizing loss channels involved in chromophore diffusion. Herein, we present a study of photon upconversion by TTA internally within a polymeric annihilator network (iTTA). By the design of the annihilator polymer and the choice of experiment conditions, we isolate upconversion emission governed by iTTA within the annihilator particles and eliminate possible external TTA between separate annihilator particles (xTTA). This approach leads to mechanistic insights into the process of iTTA and makes it possible to explore the upconversion kinetics and performance of a polymeric annihilator. In comparison to a monomeric upconversion system that only functions using xTTA, we show that upconversion in a polymeric annihilator is efficient also at extremely low annihilator concentrations and that the overall kinetics is significantly faster. The presented results show that intramolecular photon upconversion is a versatile concept for the development of highly efficient solid-state photon upconversion materials.
Project description:Photolysis has enabled the occurrence of numerous discoveries in chemistry, drug discovery and biology. However, there is a dearth of efficient long wavelength light mediated photolysis. Here, we report general and efficient long wavelength single photon method for a wide array of photolytic molecules via triplet-triplet annihilation photolysis. This method is versatile and "LEGO"-like. The light partners (the photosensitizers and the photolytic molecules) can be energetically matched to adapt to an extensive range of electromagnetic spectrum wavelengths and the diversified chemical structures of photoremovable protecting groups, photolabile linkages, as well as a broad array of targeted molecules. Compared to the existing photolysis methods, our strategy of triplet-triplet annihilation photolysis not only exhibits superior reaction yields, but also resolves the photodamage problem, regardless of whether they are single photon or multiple photon associated. Furthermore, the biological promise of this "LEGO" system was illustrated via developing ambient air-stable nanoparticles capable of triplet-triplet annihilation photolysis.
Project description:Strong light-matter coupling generates hybrid states that inherit properties of both light and matter, effectively allowing the modification of the molecular potential energy landscape. This phenomenon opens up a plethora of options for manipulating the properties of molecules, with a broad range of applications in photochemistry and photophysics. In this article, we use strong light-matter coupling to transform an endothermic triplet-triplet annihilation process into an exothermic one. The resulting gradual on-off photon upconversion experiment demonstrates a direct conversion between molecular states and hybrid light-matter states. Our study provides a direct evidence that energy can relax from nonresonant low energy molecular states directly into hybrid light-matter states and lays the groundwork for tunable photon upconversion systems that modify molecular properties in situ by optical cavities rather than with chemical modifications.
Project description:A photoresponsive nanoporous polymer film has been produced from the templated self-assembly of a columnar liquid crystal containing azo units. A liquid crystalline complex of polymerizable azobenzoic acid and a tris-benzimidazolyl benzene template molecule was cross-linked via thiol-ene radical copolymerization with dodecanedithiol. Subsequent removal of the template yielded nanoporous polymer films with pores of approximately 1 nm in diameter. Both trans-cis and cis-trans photoisomerizations of azobenzoic acid took place in the porous films. At room temperature, the cis isomer was sufficiently long-lived to establish a difference in dye absorption kinetics of the two isomers. The cationic dye rhodamine 6G was bound to both isomers, but the rate of binding to films enriched in the cis isomer was 8 times faster.