Fluorescent molecular system

With an aim to establish a basis for a fibro-optic biosensoring, a number of fluorescence molecular systems were immobilized on quartz surface and investigated. 

Under continuous-wave excitation of a fluorescent molecular system, typically in solution or in solid samples, it is possible to record absorption, fluorescence (both emission and excitation spectra) and phosphorescence spectra. 

PL is often referred to as fluorescence spectrometry or fluorometry, especially when applied to molecular systems. Uses for PL are found in many fields, including... 

Kollmannsberger M, Rurack K, Resch-Genger U et al (2000) Design of an efficient charge-transfer processing molecular system containing a weak electron donor spectroscopic and redox properties and cation-induced fluorescence enhancement. Chem Phys Lett 329 363-369... 

W. Rettig, R. Fritz, and J. Springer, Fluorescence probes based on adiabatic photochemical reactions, in Photochemical Processes in Organized Molecular Systems (K. Honda, ed.), p. 61, Elsevier Science Publishers, Amsterdam (1991). 

The possibility to carry out conformational studies of peptides at low concentrations and in the presence of complex biological systems represents a major advantage of fluorescence spectroscopy over other techniques. Fluorescence quantum yield or lifetime determinations, anisotropy measurements and singlet-singlet resonance energy transfer experiments can be used to study the interaction of peptides with lipid micelles, membranes, proteins, or receptors. These fluorescence techniques can be used to determine binding parameters and to elucidate conformational aspects of the interaction of the peptide with a particular macro-molecular system. The limited scope of this chapter does not permit a comprehensive review of the numerous studies of this kind that have been carried and only a few general aspects are briefly discussed here. Fluorescence studies of peptide interactions with macromolecular systems published prior to 1984 have been reviewed. 

TTF-based D-A systems have been extensively used in recent years to play around photoinduced electron transfer processes. Typically, when an electron acceptor moiety that emits fluorescence intrinsically is linked to TTF (D), the fluorescence due to the A moiety may be quenched because of a photoinduced electron transfer process (Scheme 15.1). Accordingly, these molecular systems are potentially interesting for photovoltaic studies. For instance, efficient photoinduced electron transfer and charge separation were reported for TTF-fullerene dyads.6,7 An important added value provided by TTF relies on the redox behavior of this unit that can be reversibly oxidized according to two successive redox steps. Therefore, such TTF-A assemblies allow an efficient entry to redox fluorescence switches, for which the fluorescent state of the fluorophore A can be reversibly switched on upon oxidation of the TTF unit. 

Finally, it should be noted that other spectral analyses such as Raman, nuclear magnetic resonance, and fluorescence spectroscopies, which are correlated to more local chemical entities or individual atoms in the molecular systems, complement the CD data. Although other spectral approaches may provide more effective tools for analyzing a local structure or individual atoms in the molecular systems than the CD does, the CD approach is indispensable for the estimation of change or population in chiral structures on the average. 

The LB deposition is one of the best methods to prepare highly organized molecular systems, in which various molecular parameters such as distance, orientation, extent of chromophore interaction, or redox potential can be controlled in each monolayer. We have been studying photophysical and photochemical properties of LB films in order to construct molecular electronic and photonic devices. The molecular orientation and interactions of redox chromophores are very important in controlling photoresponses at the molecular level. Absorption and fluorescence spectra give important information on them. We have studied photoresponses, specific interactions, and in-plane and out-of-plane orientation of various chromophores in LB films [3-11], In addition to the change of absorp-... 

The fluorescence phenomenon is highly probable in molecular systems containing atoms with lone pairs of electrons such as C=0, aromatic, phenolic, quinone, and... 

The present analysis relies on - and extends - the comprehensive theoretical study of Refs. [23,24] on the multi-state interactions in the manifold of the X — E states of Bz+. Like this recent work, it utilizes an ab initio quantum-dynamical approach. In Refs. [23,24] we have, in addition, identified strong coupling effects between the B — C and B — D electronic states, caused by additional conical intersections between their potential energy surfaces. A whole sequence of stepwise femtosecond internal conversion processes results [24]. Such sequential internal conversion processes are of general importance as is evidenced indirectly by the fluorescence and fragmentation dynamics of organic closed-shell molecules and radical cations [49,50]. It is therefore to be expected that the present approach and results may be of relevance for many other medium-sized molecular systems. 

When deciding to study the dynamics of electronic excitation energy transfer in molecular systems by conventional spectroscopic techniques (in contrast to those based on non-linear properties such as photon echo spectroscopy) one has the choice between time-resolved fluorescence and transient absorption. This choice is not inconsequential because the two techniques do not necessarily monitor the same populations. Fluorescence is a very sensitive technique, in the sense that single photons can be detected. In contrast to transient absorption, it monitors solely excited state populations this is the reason for our choice. But, when dealing with DNA components whose quantum yield is as low as 10-4, [3,30] such experiments are far from trivial. 

Because of the multifunctional nature of these photochromic systems, the change in chirality simultaneously triggers the modulation of some particular function, such as fluorescence, molecular recognition, or motion. In most cases, this is the result of a change in the geometry or the electronic properties of the system. 

---