› › Photoinduced Intramolecular Charge Transfer In Donor Acceptor Biaryls And Resulting Applicational Aspects Regarding Fluorescent Probes And Solar Energy Conversion

Photoinduced Intramolecular Charge Transfer in Donor-Acceptor Biaryls and Resulting Applicational Aspects Regarding Fluorescent Probes and Solar Energy Conversion

Author : Michael Maus

Publisher : Universal-Publishers

Page : 223 pages

File Size : 45,25 MB

Release : 1998

Category : Technology & Engineering

ISBN : 1581120303

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This study is focused on the effects of photoinduced intramolecular charge transfer (CT) in three differently twisted donor-acceptor (D-A) biphenyls. Taking into account a further pair of differently twisted D-A biaryls new universal insights into the photoinduced electronic and conformation dynamics of D-A biaryls are obtained. Furthermore, possible applications in fields of solar energy conversion and fluorescence sensing of microenvironments are demonstrated. Experimental means of stationary and time-resolved (ps to s) luminescence, transient absorption (sub-ps), polarization spectroscopy, high pressure and low temperature techniques are employed in conjunction with quantum chemical calculations. Twist angle and solvent dependent electron transfer (ET) interactions between the D and A aryl moieties are responsible for the low lying and solvatochromic intramolecular CT electron band which gains unusually high intensity through strong electronic coupling of the pure 1ET with the ground (S0) and 1La state. As regards the class of biaryl compounds, for the first time, an excited state electron transfer from the D to the A could be monitored by dual spectrally separated stimulated fluorescence bands with precursor-successor relationship on a sub-ps timescale for the D-A biphenyls. It is concluded that, in additon to the electronic interaction of 1ET with S0 and 1La, the electronic interaction with a close lying 1Lb state plays a fundamental role in the ET dynamics and the 1CT-S0 transition probability in D-A biaryls. The initial photoinduced conformational relaxation occurs towards planarity in all biaryls investigated. However, various results evidence that the highly twisted D-A biphenyl additionally performs a slow "excited state intramolecular back twist rotation" leading to a solvent polarity dependent conformational equilibrium between a more planar (CT) and a more twisted (CTR) conformer in S1(1CT). Using global analysis of the biexponential fluorescence decays as a function of temperature and pressure in medium polar solvents, the kinetics, thermodynamics, viscosity control and decomposed emission spectra associated with this adiabatic photoreaction are determined. The twist angle dependent ability of the D-A biphenyls to serve as fluorescent probes of micropolarity, changes of microviscosity or matrix order, protic solvents and pH is investigated. In particular, fluorescence sensing of pH seems to be promising.





Polymers in Organic Electronics

Author : Sulaiman Khalifeh

Publisher : Elsevier

Page : 617 pages

File Size : 36,18 MB

Release : 2020-04-01

Category : Technology & Engineering

ISBN : 192788568X

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Book Description

Polymers in Organic Electronics: Polymer Selection for Electronic, Mechatronic, and Optoelectronic Systems provides readers with vital data, guidelines, and techniques for optimally designing organic electronic systems using novel polymers. The book classifies polymer families, types, complexes, composites, nanocomposites, compounds, and small molecules while also providing an introduction to the fundamental principles of polymers and electronics. Features information on concepts and optimized types of electronics and a classification system of electronic polymers, including piezoelectric and pyroelectric, optoelectronic, mechatronic, organic electronic complexes, and more. The book is designed to help readers select the optimized material for structuring their organic electronic system.Chapters discuss the most common properties of electronic polymers, methods of optimization, and polymeric-structured printed circuit boards. The polymeric structures of optoelectronics and photonics are covered and the book concludes with a chapter emphasizing the importance of polymeric structures for packaging of electronic devices. Provides key identifying details on a range of polymers, micro-polymers, nano-polymers, resins, hydrocarbons, and oligomers Covers the most common electrical, electronic, and optical properties of electronic polymers Describes the underlying theories on the mechanics of polymer conductivity Discusses polymeric structured printed circuit boards, including their rapid prototyping and optimizing their polymeric structures Shows optimization methods for both polymeric structures of organic active electronic components and organic passive electronic components



Photoinduced Charge and Energy Transfer Processes in Molecular Aggregates

Author :

Publisher :

Page : pages

File Size : 35,23 MB

Release : 2009

Category :

ISBN :

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This project involved the experimental probing of the electronic excited states generated by photoinduced (center-to-center) electron and energy transfer processes in several classes of transition metal donor/acceptor (D/A) complexes. Some of the general properties inferred from these studies should be useful in the design of new systems for energy conversion applications. Pursuit of the project goals has involved the determination of electron transfer efficiencies and the detailed study of variations in the electronic spectra of D/A complexes. This has resulted in the study of some very fundamental issues of photoinduced charge transfer and the identification of some of the constraints on its efficiency. The experimental studies of the competition between the degradative non-radiative unimolecular relaxation of transition metal excited states and their transfer of charge from these excited states to external acceptors have involved a range of techniques such as transient decay kinetics, photoacoustic calorimetry and transient or stationary state spectroscopy. The substrates synthesized for these studies were selected to provide model systems, or series of model systems to probe the validity of models of electronic excited states and their reactivity. The work during the last few years has focused largely, but not exclusively, on the use of emission spectral band shapes to probe the properties of charge transfer (CT) excited states. Bandshape variations are one of the very few approaches for systematically probing electronic excited states and good band shape resolution is necessary in order to gain information about the structural variations that correlate with excited state reactivity. Differences in molecular structure correlate with differences in chemical reactivity, and the variations in emission bandshapes are well known to relate to variations in the molecular structural differences between the excited and ground electronic states. However, it is has been rarely noticed that configurational mixing of the lowest energy excited state with other electronic states leads to unique distortions of the lowest energy excited state which result in modifications in the vibronic structure and bandshape of the emission. We have used the emission sideband shapes to evaluate patterns of ground state-excited state and excited state-excited state configurational mixing in some simple series of complexes.



Charge-transfer and Other Excitonic State in Conjugated Polymer

Author : Dhanashree Moghe

Publisher :

Page : pages

File Size : 27,58 MB

Release : 2014

Category : Electronic dissertations

ISBN :

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Book Description

Over the last few decades there has been tremendous progress in organic photovoltaics (OPVs), with efficiencies reaching over 10%. Still, many factors including the origin and the dynamics of charge carrier involved are debatable. New and sensitive techniques are constantly being devised to identify the origin of free charges. At the same time, a lot of research has also been devoted to synthesize low bandgap material such that its absorption spectra overlap with that of the solar spectrum. The most important hindrance in organic semiconductors is the formation of bound electron-hole (exciton) charge pair upon photoexcitation. Additional energy is required to dissociate the bound pair to generate free charges for photovoltaic application. The most popular and efficient way to dissociate excitons is to fabricate a bulk heterojunction solar cell, which comprises of a blend of at least two polymers: one donor and the other acceptor. It is very well established that the presence of fullerene (acceptor) helps in transfer of the negative charges from the donor polymer to fullerene, making the exciton slightly less bound. The nanometer scale islands further help in migration of charges. A crucial aspect of our studies has been evaluating the role of various excitonic states such as charge-transfer and triplet excitonic states in device efficiencies. The focus of this work was on diketopyrrolopyrrole (DPP)- based donor-acceptor (D-A) type conjugated copolymers which have low bandgap energies and have been known to show high efficiency in organic photovoltaics. These copolymers have D-A unit present in the same chain, which lowers the optical bandgap of the material. Variation of either the donor or the acceptor fraction offers an option to tune the optical bandgap by using the same D-A chromophores. The D-A configuration also results in the separation of positive and negative charges within the same polymeric chain, which is the intramolecular charge-transfer excitonic state. We analyze the intramolecular charge-transfer state using bias dependent absorption studies, which allowed us to estimate the binding energy of intramolecular exciton. Later, we performed density functional theory (DFT) and time dependent DFT calculations to identify the origin of the intramolecular exciton absorption. Taking the copolymers as donor (and fullerene as acceptor) in an organic photovoltaic device, we probe the (intermolecular) charge-transfer states formed at the copolymer/fullerene interface . We utilize monochromatic photocurrent method and a highly sensitive (and fast) Fourier transform photocurrent spectroscopy technique to probe the intermolecular charge-transfer states in the device. Our analyses show that the optical bandgap difference between the copolymers and fullerene plays a pivotal role in stabilization /destabilization of charge - transfer states in copolymer-fullerene systems. The triplet excitons are also known to play an important role in OPV efficiency. We probe the diffusion length of triplet exciton in ladder-type polymers by devising a simple, yet efficient method using optical modulation spectroscopy (photoinduced absorption spectroscopy). The diffusion length of triplet excitons is estimated to be almost three orders of magnitude more than the singlet excitons . Further, by implementing a 1D random-walk model to the photoinduced absorption data, we estimate diffusivities of the triplet exciton in our sample.





Photoinduced Electron Transfer from a Fundamental Understanding to Potential Applications

Author : Natalie Renuka Banerji

Publisher :

Page : 399 pages

File Size : 33,83 MB

Release : 2009

Category :

ISBN :

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Although the transfer of an electron from a donor to an acceptor after one of them has been electronically excited by the absorption of light appears to be a very simple reaction, there are still many open questions concerning the detailed mechanism of photoinduced electron transfer. It is nevertheless a fascinating and very important reaction, given its key importance in photosynthesis and many modern approaches to solar energy conversion. The objective of this PhD thesis was thus to use ultrafast, femtosecond-resolved spectroscopy in order to gain a better insight to photoinduced electron transfer occuring for closed-shell organic molecules in liquid solution, in particular where the relative geometry of the reaction partners is concerned. The investigations span a large variety of electron donor-acceptor systems, ranging from the intramolecular to the bimolecular case and from simple model systems to complex architectures with potential apllications in solar energy coversion.



Ultrafast Photoinduced Energy and Electron Transfer Studies in Closely Bound Molecular and Nanocarbon Donor-Acceptor Systems

Author : Habtom Berhane Gobeze

Publisher :

Page : 306 pages

File Size : 14,18 MB

Release : 2018

Category : Charge exchange

ISBN :

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As part of the study, photosynthetic system constructs based on BF2-chelated dipyrromethene (BODIPY), BF2-chelated azadipyrromethene (AzaBODIPY), porphyrin, phthalocyanine, oxasmaragdyrin, polythiophene, fullerene (C60), single-walled carbon nanotube and graphene are investigated. Antenna systems of BODIPY dyads and oligomers having BODIPY as an excitation energy donor connected to different acceptors including BODIPY, azaBODIPY, oxasmaragdyrin and aluminum porphyrin are studied. Different synthetic methodologies are used to afford donor-acceptor systems either directly linked with no spacer or with short spacers of varying length and orientation. The effect of donor orientation, donor optical gap as well as nature of donor-acceptor coupling on the donor-acceptor spectral overlap and hence the rate of excitation energy transfer is investigated. In all these systems, an ultrafast energy transfer followed by electron transfer is observed. In particular, in a directly connected BODIPY-azaBODIPY dyad an unusually ultrafast energy transfer (̃ 150−200 f̧ ' ) via F©œrster mechanism is observed. The observation of energy transfer via F©œrster instead of Dexter mechanism in such closely coupled donor-acceptor systems shows the balance between spatial and electronic coupling achieved in the donor-acceptor system. Moreover, in donor-acceptor systems involving semiconducting 1D and 2D materials, covalently functionalized single-walled carbon nanotubes via charge stabilizing (TPA)3ZnP and noncovalently hybridized exfoliated graphene via polythiophene chromophores are studied for their charge transportation functions. In both cases, not only an ultrafast charge transfer in the range of (̃ 2−5 p̧ ' ) is observed but also the charge-separated states were long lived implying the potential of these functionalized materials as efficient charge transporting substrates with organic chromophores for photovoltaic and optoelectronic applications where ultrafast intercomponent charge transfer is vital. In addition, as a final part of this dissertation, the mechanisms of electron injection and back electron transfer in heterogeneous systems involving supramolecularly anchored high potential chromophores on TiO2 film are studied by femtosecond transient absorption spectroscopy. In this study, not only are important insights gained on the utilization of supramolecular anchoring of chromophores such as porphyrins, phthalocyanines, and their perflorinated high potential analogues, chromophores currently showing promise as highly efficient sensitizers in dye sensitized solar cells, on TiO2 film but also on the effect of anchor length and sensitizer orientation on the rates of electron injection and back electron transfer at the sensitizer-TiO2 interface.



Photoinduced Charge Separation in Linked Donor-acceptor-chromophore Systems . Final Report

Author :

Publisher :

Page : pages

File Size : 25,15 MB

Release : 2001

Category :

ISBN :

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A major experimental challenge in any study of intramolecular donor/acceptor (D/A) interactions is separating the variables which affect coupling. This is especially difficult when trying to evaluate the extent of through-bond superexchange. The systems of dinuclear complexes described below are unique in that the D/A connectivity can be varied without concomitant changes in D/A separation and relative orientation. Consequently, it has been possible to experimentally evaluate the effect of D/A linkage on coupling without introducing ambiguities from other structural changes. Furthermore, some of these systems are amenable to detailed theoretical treatment which allows quantitative comparisons between experiment and theory. A much more detailed picture of the D/A interaction is, thus, provided. Sections of this report include: unique structural aspects of[M(BBA)[sub 3]M[prime]] complexes; energy transfer in photoexcited[Ru(II)(BBA)[sub 3]Fe(II)][sup 4+] complexes; electrochemical investigation of[Fe(BBA)[sub 3]Fe][sup 4+]; optically-induced electron transfer in[Fe(II)(BBA)[sub 3]Fe(III)][sup 5+] mixed-valent complexes, where BBA=[alpha], [omega]-bisbipyridylalkane.



Intramolecular Charge Transfer Complexes as Fluorescence Probes for UV and Visible Light Induced Acrylate Polymerization

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Publisher :

Page : 8 pages

File Size : 10,29 MB

Release : 1994

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ISBN :

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Intramolecular charge transfer complexes (ICTC) of derivatives of 1- diaminonaphthalene-5-sulfonamide (DANSYL AMIDE) such as 1-dimethylamino- naphthalene-5-sulfonyl-n-butylamide (1,5-DASB) and 2-dimethylamino-naphthalene- 5-sulfonyl-n-butylamide (2,5DASB), were used as fluorescence probes for cure monitoring of photocurable polymer systems. This technique is based upon the difference in fluorescence intensity from the parallel and perpendicular conformations of the excited state of the complex, and is based on the dependence of the relative population of each conformation on the microviscosity of the system. As the curing reaction proceeds, the steady state fluorescence emission spectra of the probes were all found to exhibit hypsochromic spectral shifts due to the increase in matrix microviscosity. A linear correlation between the fluorescence intensity ratios (R=Ipar. / Iper.) and the extent of polymerization, measured by transmission FTIR spectrometry, was obtained for different types of acrylated polymers, cured with UV or visible (VIS) initiators. Intramolecular charge transfer, Visible light induced acrylate polymerization.