chromophore
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In this review we first provide an introductory description of the singlet fission phenomenon and then describe the ground and electronically excited states of the parent 1,3-diphenylisobenzofuran chromophore (1) and about a dozen of its derivatives. A discussion of singlet fission in thin polycrystalline layers of these materials follows. The highest quantum yield of triplet formation by singlet fission, 200% at 80 K, is found in one of the two known crystal modification of the parent. In the other modification and in many derivatives, excimer formation competes successfully and triplet yields are low. A description of solution photophysics of covalent dimers is described in the next section. Triplet yields are very low, but interesting phenomena are uncovered. One is an observation of a separated-charges (charge-transfer) intermediate in highly polar solvents. The other is an observation of excitation isomerism in both singlet and triplet states, where in one isomer the excitation is delocalized over both halves of the covalent dimer, whereas in the other it is localized on one of the halves. In the last section we present the operation of a simple device illustrating the use of triplets generated by singlet fission for charge separation.
- Klíčová slova
- 1,3-Diphenylisobenzofuran, Covalent dimers, Photophysics, Singlet fission, Solar energy,
- MeSH
- benzofurany chemie MeSH
- chemické modely * MeSH
- elektrony MeSH
- kvantová teorie MeSH
- rozpouštědla chemie MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
- Názvy látek
- 1,3-diphenylisobenzofuran MeSH Prohlížeč
- benzofurany MeSH
- rozpouštědla MeSH
Many of the UV-induced phenomena observed experimentally for aqueous cytidine were lacking the mechanistic interpretation for decades. These processes include the substantial population of the puzzling long-lived dark state, photohydration, cytidine to uridine conversion and oxazolidinone formation. Here, we present quantum-chemical simulations of excited-state spectra and potential energy surfaces of N1-methylcytosine clustered with two water molecules using the second-order approximate coupled cluster (CC2), complete active space with second-order perturbation theory (CASPT2), and multireference configuration interaction with single and double excitation (MR-CISD) methods. We argue that the assignment of the long-lived dark state to a singlet nπ* excitation involving water-chromophore electron transfer might serve as an explanation for the numerous experimental observations. While our simulated spectra for the state are in excellent agreement with experimentally acquired data, the electron-driven proton transfer process occurring on the surface may initiate the subsequent damage in the vibrationally hot ground state of the chromophore.
UV-induced photolysis of aqueous guanine nucleosides produces 8-oxo-guanine and Fapy-guanine, which can induce various types of cellular malfunction. The mechanistic rationale underlying photodestructive processes of guanine nucleosides is still largely obscure. Here, we employ accurate quantum chemical calculations and demonstrate that an excited-state non-bonding interaction of guanosine and a water molecule facilitates the electron-driven proton transfer process from water to the chromophore fragment. This subsequently allows for the formation of a crucial intermediate, namely guanosine photohydrate. Further (photo)chemical reactions of this intermediate lead to the known products of guanine photodamage.
- MeSH
- elektrony MeSH
- guanin chemie MeSH
- guanosin * chemie MeSH
- nukleosidy chemie MeSH
- voda * chemie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- guanin MeSH
- guanosin * MeSH
- nukleosidy MeSH
- voda * MeSH
The compounds I-IV derived from α-D-cyclodextrin moiety by bridging and/or interconnecting with various patterns of disulfide bonds were chosen as models for the spectroscopic study of conformation of the disulfide bridge. The energy gap between the disulfide and cyclodextrin's electronic transitions allows us to investigate absorption and electronic circular dichroism spectra without disturbing spectral overlaps with amides or aromatic amino acids in peptides or proteins. Raman optical activity (ROA) spectra were measured and the bands due to S-S and C-S stretching motion identified. Comparison with the quantum mechanical calculations of simple models indicates that sense of disulfide twist follows sign of the measured S-S ROA band.
Improving the performance of p-type photoelectrodes represents a key challenge toward significant advancement in the field of tandem dye-sensitized solar cells. Herein, we demonstrate the application of boron-doped nanocrystalline diamond (B:NCD) thin films, covalently functionalized with a dithienopyrrole-benzothiadiazole push-pull chromophore, as alternative photocathodes. First, a primary functional handle is introduced on H-terminated diamond via electrochemical diazonium grafting. Afterwards, Sonogashira cross-coupling and Cu(i) catalyzed azide-alkyne cycloaddition (CuAAC) reactions are employed to attach the chromophore, enabling the comparison of the degree of surface functionalization and the importance of the employed linker at the diamond-dye interface. X-ray photoelectron spectroscopy shows that surface functionalization via CuAAC results in a slightly higher chromophore coverage compared to the Sonogashira cross-coupling. However, photocurrents and photovoltages, obtained by photoelectrochemical and Kelvin probe measurements, are approximately three times larger on photocathodes functionalized via Sonogashira cross-coupling. Surface functionalization via Sonogashira cross-coupling is thus considered the preferential method for the development of diamond-based hybrid photovoltaics.
- Publikační typ
- časopisecké články MeSH
Time-dependent fluorescence shifts (TDFS) of chromophores selectively attached to proteins may give information on the dynamics of the probed protein moieties and their degree of hydration. Previously, we demonstrated that a coumarin dye selectively labeling the tunnel mouth of different haloalkane dehalogenases (HLDs) can distinguish between different widths of tunnel mouth openings. In order to generalize those findings analogous experiments were performed using a different chromophore probing the same region of these enzymes. To this end we synthesized and characterized three new fluorescent probes derived from dimethylaminonaphthalene bearing a linker almost identical to that of the coumarin dye used in our previous study. Labeling efficiencies, acrylamide quenching, fluorescence anisotropies, and TDFS for the examined fluorescent substrates confirm the picture gained from the coumarin studies: the different tunnel mouth opening, predicted by crystal structures, is reflected in the hydration and tunnel mouth dynamics of the investigated HLDs. Comparison of the TDFS reported by the coumarin dye with those obtained with the new dimethylaminonaphthalene dyes shows that the choice of chromophore may strongly influence the recorded TDFS characteristics. The intrinsic design of our labeling strategy and the variation of the linker length ensure that both dyes probe the identical enzyme region; moreover, the covalently fixed position of the chromophore does not allow for a major relocalization within the HLD structures. Our study shows, for the first time, that TDFS may strongly depend on the choice of the chromophore, even though the identical region of a protein is explored.
- MeSH
- Bradyrhizobium enzymologie MeSH
- fluorescence MeSH
- fluorescenční barviva chemie MeSH
- fluorescenční polarizace MeSH
- hydrolasy chemie MeSH
- kumariny chemie MeSH
- naftaleny chemie MeSH
- Rhodococcus enzymologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- coumarin MeSH Prohlížeč
- fluorescenční barviva MeSH
- haloalkane dehalogenase MeSH Prohlížeč
- hydrolasy MeSH
- kumariny MeSH
- naftaleny MeSH
Of the five small biradicaloid heterocycles whose S(1), S(2), T(1), and T(2) adiabatic excitation energies were examined by the CASPT2/ANO-L-VTZP method, two have been found to meet the state energy criterion for efficient singlet fission and are recommended to the attention of synthetic chemists and photophysicists.
- Publikační typ
- časopisecké články MeSH
Photoreceptors containing the light-oxygen-voltage (LOV) domain elicit biological responses upon excitation of their flavin mononucleotide (FMN) chromophore by blue light. The mechanism and kinetics of dark-state recovery are not well understood. Here we incorporated the non-canonical amino acid p-cyanophenylalanine (CNF) by genetic code expansion technology at 45 positions of the bacterial transcription factor EL222. Screening of light-induced changes in infrared (IR) absorption frequency, electric field and hydration of the nitrile groups identified residues CNF31 and CNF35 as reporters of monomer/oligomer and caged/decaged equilibria, respectively. Time-resolved multi-probe UV/visible and IR spectroscopy experiments of the lit-to-dark transition revealed four dynamical events. Predominantly, rearrangements around the A'α helix interface (CNF31 and CNF35) precede FMN-cysteinyl adduct scission, folding of α-helices (amide bands), and relaxation of residue CNF151. This study illustrates the importance of characterizing all parts of a protein and suggests a key role for the N-terminal A'α extension of the LOV domain in controlling EL222 photocycle length.
- Klíčová slova
- FTIR spectroscopy, UV/vis spectroscopy, flavoproteins, genetic code expansion, kinetics, photosensory receptors, protein structural dynamics, signal transduction, site-specific vibrational probes, time-resolved methods,
- MeSH
- aminokyseliny * metabolismus MeSH
- flavinmononukleotid * chemie MeSH
- regulace genové exprese MeSH
- transkripční faktory metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- aminokyseliny * MeSH
- flavinmononukleotid * MeSH
- transkripční faktory MeSH
Research activities in the field of imidazole-derived push-pull systems featuring intramolecular charge transfer (ICT) are reviewed. Design, synthetic pathways, linear and nonlinear optical properties, electrochemistry, structure-property relationships, and the prospective application of such D-π-A organic materials are described. This review focuses on Y-shaped imidazoles, bi- and diimidazoles, benzimidazoles, bis(benzimidazoles), imidazole-4,5-dicarbonitriles, and imidazole-derived chromophores chemically bound to a polymer chain.
- Klíčová slova
- charge transfer, chromophore, conjugation, donor–acceptor system, imidazole,
- Publikační typ
- časopisecké články MeSH
The coherent third order optical response of molecular aggregates with fluctuating frequencies, couplings, and transition dipole moments is studied. We derived stochastic nonlinear exciton equations (SNEEs) by combining the quasiparticle picture of excitons with the path integral over stochastic bath paths described by the stochastic Liouville equations. Coherent two-dimensional (2D) spectra are calculated for a tetramer model system whose transition dipole orientations undergo two-state stochastic jumps on an arbitrary timescale. Correspondence between domains of ordered dipoles, which determine the exciton coherence length and the absorption peaks, is established. Signatures of domain coherence length fluctuations are observed in the cross peak dynamics of the 2D spectra in specific pulse polarization configurations.
- MeSH
- barva MeSH
- elektrony * MeSH
- Markovovy řetězce MeSH
- optické jevy * MeSH
- spektrální analýza * MeSH
- stochastické procesy MeSH
- teoretické modely MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, N.I.H., Extramural MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
