| 1. |
- Edhborg, Fredrik, 1990, et al.
(författare)
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Triplet States of Cyanostar and Its Anion Complexes
- 2023
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Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 127:28, s. 5841-5850
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Tidskriftsartikel (refereegranskat)abstract
- The design of advanced optical materials based on triplet states requires knowledge of the triplet energies of the molecular building blocks. To this end, we report the triplet energy of cyanostar (CS) macrocycles, which are the key structure-directing units of small-molecule ionic isolation lattices (SMILES) that have emerged as programmable optical materials. Cyanostar is a cyclic pentamer of covalently linked cyanostilbene units that form π-stacked dimers when binding anions as 2:1 complexes. The triplet energies, ET, of the parent cyanostar and its 2:1 complex around PF6- are measured to be 1.96 and 2.02 eV, respectively, using phosphorescence quenching studies at room temperature. The similarity of these triplet energies suggests that anion complexation leaves the triplet energy relatively unchanged. Similar energies (2.0 and 1.98 eV, respectively) were also obtained from phosphorescence spectra of the iodinated form, I-CS, and of complexes formed with PF6- and IO4- recorded at 85 K in an organic glass. Thus, measures of the triplet energies likely reflect geometries close to those of the ground state either directly by triplet energy transfer to the ground state or indirectly by using frozen media to inhibit relaxation. Density functional theory (DFT) and time-dependent DFT were undertaken on a cyanostar analogue, CSH, to examine the triplet state. The triplet excitation localizes on a single olefin whether in the single cyanostar or its π-stacked dimer. Restriction of the geometrical changes by forming either a dimer of macrocycles, (CSH)2, or a complex, (CSH)2·PF6-, reduces the relaxation resulting in an adiabatic energy of the triplet state of 2.0 eV. This structural constraint is also expected for solid-state SMILES materials. The obtained T1 energy of 2.0 eV is a key guide line for the design of SMILES materials for the manipulation of triplet excitons by triplet state engineering in the future.
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| 2. |
- Simonsen, J. B., et al.
(författare)
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Columnar Self-Assembly and Alignment of Planar Carbenium Ions in Langmuir-Blodgett Films
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 27:2, s. 792-799
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Tidskriftsartikel (refereegranskat)abstract
- Structural and optical properties of multilayer Langmuir-Blodgett (LB) films of two amphiphilic carbenium salts 2-didecylamino-6,10-bis(dimethylamino)-4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-1) and 2,6-bis-(decylmethylamino)-10-dimethylamino-4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-2) are described. The LB films were prepared on lipophilic glass by standard vertical dipping. Grazing incidence X-ray diffraction (GIXD) measurements show that the planar organic cores, in spite of their positive charge, form closely packed columns with a repeating distance of similar to 3.45 angstrom. Specular X-ray reflectivity (SXR) reveals the LB multilayers to consist of Y-type bilayers with thickness 31 angstrom for ATOTA-1 and 41 angstrom for ATOTA-2. This significant difference is ascribed to the different packing motifs of the alkyl chains in the two LB films. GIXD and polarized UV-vis absorption and emission spectroscopy show that the columnar aggregates in the LB films are oriented along the dipping direction. This alignment is attributed to shear effects during LB transfer. The main absorption band of the LB films is blue-shifted compared to that in solution, while the fluorescence is red-shifted by more than 100 nm. These findings suggest the presence of H-aggregates in agreement with the cofacial packing derived from the X-ray measurements. Polarized absorption spectroscopy with variable angle of incidence was used to resolve two perpendicular optical transitions in the visible range, one at 460 nm polarized perpendicular to the columnar direction, in the plane of the film, and one at 420 nm polarized along the film normal.
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| 3. |
- Sorensen, T. J., et al.
(författare)
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Large area, soft crystalline thin films of N,N ',N ''-trialkyltriazatriangulenium salts with homeotropic alignment of the discotic cores in a lamellar lattice
- 2012
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 22:11, s. 4797-4805
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Tidskriftsartikel (refereegranskat)abstract
- N,N',N ''-Trialkyltriazatriangulenium (R-TATA(+)) tetrafluoroborate (BF4-) salts form highly ordered thin films directly when spin-cast onto rotating substrates. The homogeneous and crystalline thin films show macroscopic order over centimetres. The crystal structures of the R-TATA center dot BF4 salts are investigated and compared for the propyl, 3-methylpentyl and octyl derivatives. In all cases the molecules pack in hexagonally ordered bilayers, with segregation of the ionic groups and the alkyl chains. This is a rare packing motif with the rigid discotic TATA(+) cores organized co-planarly in sheets separated by perpendicularly oriented alkyl chains, somewhat similar to a crystallized lamellar phase of phospholipid bilayers and the lamellar smectic mesophase of liquid crystals. The structure of the thin films is investigated by optical spectroscopy, X-ray reflectometry and grazing incidence X-ray diffraction. All techniques confirm that the 15-30 nm thick films maintain the lamellar structure of the bulk crystals, are flat on macroscopic length scales, and are completely ordered relative to the substrate. The triazatriangulenium molecules are electroactive dyes, and in the highly anisotropic polycrystalline thin film structure they show intense fluorescence and efficient exciton transport.
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| 4. |
- Dahl Jensen, Jesper, et al.
(författare)
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Investigating Design Rules for Photoinduced Electron Transfer Quenching in Triangulenium Probes
- 2023
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Ingår i: Chemistry - A European Journal. - 0947-6539. ; 29:46
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescent probes based on photoinduced electron transfer (PET) quenching of long lifetime triangulenium fluorophores have found multiple applications. For such probes a successful design relies on the right balance between the rate of PET quenching and fluorescence. In a series of ADOTA (A) and DAOTA (D) triangulenium fluorophores appended with aniline-like quencher moieties, we have investigated the rate of quenching and its relation to thermodynamic driving force, distance, and conjugation within the quencher moiety. Three different quenchers, a short (1), a long (2), and a long twisted (3), 4-aminophenyl, 4’-aminobiphenyl, and 2,2’-dimethyl-4’-aminobiphenyl, respectively were investigated. Steady-state spectroscopy and electrochemistry confirms that the quencher moieties are electronically decoupled from the dyes and have similar oxidation potentials and thus driving force for PET quenching, irrespectively of their different length and conjugation. Time-resolved fluorescence measurement was used to measure the fast PET quenching, with rate constant kPET ranging from >4×1011 to 2×109 s−1. Interestingly, PET quenching is equally efficient/fast from 1 and 2, even with increase in distance between the donor and the acceptor. However, when twisting the biphenyl in 3, a 20-fold decrease in quenching is found. Even with this decrease in kPET, the quenching in 3 A/D is still highly efficient, with nearly 99 % quenching. The study show that long lifetime fluorophores can be efficiently switched even by relatively slow PET processes and that PET quencher moieties can be removed far from the fluorophore if conjugated linkers are applied.
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| 5. |
- Kacenauskaite, Laura, et al.
(författare)
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Rational Design of Bright Long Fluorescence Lifetime Dyad Fluorophores for Single Molecule Imaging and Detection
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; , s. 1377-1385
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Tidskriftsartikel (refereegranskat)abstract
- Increasing demand for detecting single molecules in challenging environments has raised the bar for the fluorophores used. To achieve better resolution and/or contrast in fluorescence microscopy, it is now essential to use bright and stable dyes with tailored photophysical properties. While long fluorescence lifetime fluorophores offer many advantages in time-resolved imaging, their inherently lower molar absorption coefficient has limited applications in single molecule imaging. Here we propose a generic approach to prepare bright, long fluorescence lifetime dyad fluorophores comprising an absorbing antenna chromophore with high absorption coefficient linked to an acceptor emitter with a long fluorescence lifetime. We introduce a dyad consisting of a perylene antenna and a triangulenium emitter with 100% energy transfer from donor to acceptor. The dyad retained the long fluorescence lifetime (17 ns) and high quantum yield (75%) of the triangulenium emitter, while the perylene antenna increased the molar absorption coefficient (up to 5 times) in comparison to the free triangulenium dye. These triangulenium based dyads with significantly improved brightness can now be detected at the single molecule level and easily discriminated from bright autofluorescence by time-gated and other lifetime-based detection schemes.
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| 6. |
- Kjaer, Christina, et al.
(författare)
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Luminescence Spectroscopy of Rhodamine Homodimer Dications in Vacuo Reveals Strong Dye-Dye Interactions
- 2019
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Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 20:4, s. 533-537
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Tidskriftsartikel (refereegranskat)abstract
- Being alone or together makes a difference for the photophysics of dyes but for ionic dyes it is difficult to quantify the interactions due to solvent screening and nearby counter ions. Gas-phase luminescence experiments are desirable and now possible based on recent developments in mass spectrometry. Here we present results on tailor-made rhodamine homodimers where two dye cations are separated by methylene linkers, (CH2)(n). In solution the fluorescence is almost identical to that from the monomer whereas the emission from bare cation dimers redshifts with decreasing n. In the absence of screening, the electric field from the charge on one dye is strong enough to polarize the other dye, both in the ground state and in the excited state. An electrostatic model based on symmetric dye responses (equal induced-dipole moments in ground state) captures the underlying physics and demonstrates interaction even at large distances. Our results have possible implications for gas-phase Forster Resonance Energy Transfer.
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| 7. |
- Pedersen, Viktor B. R., et al.
(författare)
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Electronic Materials : An Antiaromatic Propeller Made from the Four-Fold Fusion of Tetraoxa[8]circulene and Perylene Diimides
- 2022
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Ingår i: Angewandte Chemie International Edition. - : Wiley-V C H Verlag GMBH. - 1433-7851 .- 1521-3773. ; 61:48
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of an antiaromatic tetraoxa[8]circulene annulated with four perylene diimides (PDI), giving a dynamic non-planar pi-conjugated system, is described. The molecule contains 32 aromatic rings surrounding one formally antiaromatic planarized cyclooctatetraene (COT). The intense absorption (epsilon=3.35x10(5) M-1 cm(-1) in CH2Cl2) and emission bands are assigned to internal charge-transfer transitions in the combined PDI-circulene pi-system. The spectroscopic data is supported by density functional theory calculations, and nuclear independent chemical shift calculation indicate that the antiaromatic COT has increased aromaticity in the reduced state. Electrochemical studies show that the compound can reversibly reach the tetra- and octa-anionic states by reduction of the four PDI units, and the deca-anionic state by reduction of the central COT ring. The material functions effectively in bulk hetero junction solar cells as a non-fullerene acceptor, reaching a power conversion efficiency of 6.4 %.
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| 8. |
- Westerlund, Fredrik, 1978, et al.
(författare)
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Direct probing of ion pair formation using a symmetric triangulenium dye
- 2011
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Ingår i: Photochemical and Photobiological Sciences. - : Springer Science and Business Media LLC. - 1474-9092 .- 1474-905X. ; 10:12, s. 1963-1973
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Tidskriftsartikel (refereegranskat)abstract
- The 2,6,10-tris(dialkylamino)trioxatriangulenium dyes (ATOTA+) are highly stabilised cationic chromophores with D3h symmetry. The symmetry gives rise to a degeneracy of the main electronic transition. In low polarity solvents significant splitting of this degenerate transition is observed and assigned to ion pair formation. Ion pairing of the 2,6,10-tris(dioctylamino)trioxatriangulenium ionwith Cl-, BF4-, PF6- and TRISPHAT anions was studied using absorption spectroscopy. A clear correlation is found between the size of the anion and the splitting of the ATOTA+ transitions. In benzene the Cl- salt displays a splitting of 1955 cm-1, while the salt of the much larger TRISPHAT ionhas a splitting of 1543 cm-1. TD-DFT calculations confirm the splitting of the states and provide a detailed insight into the electronic structure of the ion pairs. The different degree of splitting in different ion pairs is found to correlate with the magnitude of the electric field generated in each ion pair, thus leading to the conclusion that the effect seen is an internal Stark effect. By insertion of an amphiphilic derivative of the ATOTA+ chromophore in an oriented lamellar liquid crystal, it was possible to resolve the two bands of the double peak spectrum and show their perpendicular orientation in the molecular framework, as predicted by the calculations.
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| 9. |
- Westerlund, Fredrik, 1978, et al.
(författare)
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Self-Assembly and Near Perfect Macroscopic Alignment of Fluorescent Triangulenium Salt in Spin-Cast Thin Films on PTFE
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 29:22, s. 6728-6736
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Tidskriftsartikel (refereegranskat)abstract
- Highly fluorescent, discotic trioxatriangulenium dyes were aligned by simple spin-casting on substrates with friction transferred PTFE layers. The fluorescent crystalline thin films show near perfect macroscopic alignment on centimeter large areas directly from spin-casting. Gracing Incidence X-ray Diffraction (GIXD) unambiguously allowed the determination of a long-range order unit cell as well as its orientation with respect to the PTFE fibers. Further analysis of the X-ray data, in conjunction with polarized absorption spectroscopy, suggest a lamellar packing model with alternating layers of alkyl chains and ionic dyes oriented parallel to the substrate. This structure results in a highly anisotropic electrostatic potential around the cationic chromophore, causing cant shifts in energy and orientation of the optical transitions. Thus, the optical properties of the material are, to a large extent, controlled by the position of the otherwise inert PF6- counterions. The bright fluorescence from the films is also polarized parallel to the PTFE alignment layer. Doping of the thin films with fluorescent energy acceptor traps shows that efficient exciton migration takes place in the thin films. The excellent exciton transfer capabilities, in conjunction with the perfect alignment, might be of interest in future applications in solar energy harvesting or as thin film sensors.
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| 10. |
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