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Model Chromophores (model + chromophore)
Selected AbstractsEnhanced Two-Photon Absorption of Organic Chromophores: Theoretical and Experimental Assessments,ADVANCED MATERIALS, Issue 24 2008Francesca Terenziani Abstract Functional organic materials with enhanced two-photon absorption lead to new technologies in the fields of chemistry, biology, and photonics. In this article we review experimental and theoretical methodologies allowing detailed investigation and analysis of two-photon absorption properties of organic chromophores. This includes femtosecond two-photon excited fluorescence experimental setups and quantum-chemical methodologies based on time-dependent density functional theory. We thoroughly analyze physical phenomena and trends leading to large two-photon absorption responses of a few series of model chromophores focusing on the effects of symmetric and asymmetric donor/acceptor substitution and branching. [source] Accurate evaluation of the absorption maxima of retinal proteins based on a hybrid QM/MM methodJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2006Azuma Matsuura Abstract Here we improved our hybrid QM/MM methodology (Houjou et al. J Phys Chem B 2001, 105, 867) for evaluating the absorption maxima of photoreceptor proteins. The renewed method was applied to evaluation of the absorption maxima of several retinal proteins and photoactive yellow protein. The calculated absorption maxima were in good agreement with the corresponding experimental data with a computational error of <10 nm. In addition, our calculations reproduced the experimental gas-phase absorption maxima of model chromophores (protonated all-trans retinal Schiff base and deprotonated thiophenyl- p -coumarate) with the same accuracy. It is expected that our methodology allows for definitive interpretation of the spectral tuning mechanism of retinal proteins. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2006 [source] Ab Initio Quantum Chemical Investigation of the First Steps of the Photocycle of Phototropin: A Model Study,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2003Christian Neiß ABSTRACT Phototropin is a blue light,activated photoreceptor that plays a dominant role in the phototropism of plants. The protein contains two subunits that bind flavin mononucleotide (FMN), which are responsible for the initial steps of the light-induced reaction. It has been proposed that the photoexcited flavin molecule adds a cysteine residue of the protein backbone, thus activating autophosphorylation of the enzyme. In this study, the electronic properties of several FMN-related compounds in different charge and spin states are characterized by means of ab initio quantum mechanical calculations. The model compounds serve as idealized model chromophores for phototropism. Reaction energies are estimated for simple model reactions, roughly representing the addition of a cysteine residue to the flavin molecule. Excitation energies were calculated with the help of time-dependent density functional theory. On the basis of these calculations we propose the following mechanism for the addition reaction: (1) after photoexcitation of FMN out of the singlet ground state S0, excited singlet state(s) are populated; these relax to the lowest excited singlet state S1, and subsequently by intersystem crossing FMN in the lowest triplet state, T1 is formed; (2) the triplet easily removes the neutral hydrogen atom from the H,S group of the cysteine residue; and (3) the resulting thio radical is added. [source] Organic Polyaromatic Hydrocarbons as Sensitizing Model Dyes for Semiconductor NanoparticlesCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 4 2010Yongyi Zhang Abstract The study of interfacial charge-transfer processes (sensitization) of a dye bound to large-bandgap nanostructured metal oxide semiconductors, including TiO2, ZnO, and SnO2, is continuing to attract interest in various areas of renewable energy, especially for the development of dye-sensitized solar cells (DSSCs). The scope of this Review is to describe how selected model sensitizers prepared from organic polyaromatic hydrocarbons have been used over the past 15 years to elucidate, through a variety of techniques, fundamental aspects of heterogeneous charge transfer at the surface of a semiconductor. This Review does not focus on the most recent or efficient dyes, but rather on how model dyes prepared from aromatic hydrocarbons have been used, over time, in key fundamental studies of heterogeneous charge transfer. In particular, we describe model chromophores prepared from anthracene, pyrene, perylene, and azulene. As the level of complexity of the model dye-bridge-anchor group compounds has increased, the understanding of some aspects of very complex charge transfer events has improved. The knowledge acquired from the study of the described model dyes is of importance not only for DSSC development but also to other fields of science for which electronic processes at the molecule/semiconductor interface are relevant. [source] | ||||||||||