| Nowadays, material, energy and information technologies are three pillar industries. Thematerials that have close relation with our life have also been the foundation for thedevelopment of energy and information technologies. As the new member of the materialfamily, functional molecular materials have become increasingly important for manyapplications, for which the design and characterization by the theoretical modeling haveplayed the vital role. In this thesis, three different categories of organic functional molecularmaterials, the self-assembled monolayers (SAMs), the fullerene derivatives and thexanthene derivatives have been studied theoretically.X-ray spectroscopy and Raman spectroscopy technologies are two useful tools to studythe electronic and geometric structures of mater. Soft X-ray spectroscopy is a powerful toolfor studying the chemical and electronic structures of organic functional molecular materials,it is usually used to investigate the process of excitation and deexcitation. Theoreticalcalculations have been proven to be extremely useful for providing correct assignments forspectra of large systems. Raman spectroscopy is usually used to obtain the information ofvibraitional energy levels, and it has been the powerful tool to identify the molecularstructure and interaction between the molecules. These two tools characterize the electronicand geometric structures of molecule in different ways.In this thesis, by means of the first principle mehods, we studied X-ray spectroscopyincluding the X-ray photoelectron spectra (XPS) and near-edge X-ray absorption finestructure (NEXAFS) of aminothiolates SAMs and the fullerene derivatives. For thexanthene derivatives especially the Rhodamine family, we studied their Ramanspectroscopy by means of first principle mehods. Following is the brief content of thisthesis:Amine-terminated SAMs are one kind of versatile functional materials. However, theirexperimental XPS and NEXFAS spectra have long been known to be difficult to explain because of the appearance of unexpected spectral features. Different structures orhypotheses have been put forward over the years from different groups. In this study, wehave shown from theoretical calculations that the extra spectral peak in XPS spectra isresulted from new specie, named as primary ammonium that is in between protonated andhydrogen bonded structures. The X-ray damage is found to be quite common for SAMs andits products can lead to the extra spectral features in NEXFAS spectra. The possiblephoto-damaged products have been identified by comparing the experimental and calculatedspectra. This study resolves a long standing controversy on structure determination of thisuseful system that has extensive applications in biotechnology.The polymer solar cell acceptor (PSCA) molecule is one kind of organic functionalmolecular materials which have great development in the past two decades. The outstandingphysical and chemical properties bring them the wide application in terms of thedevelopment of energy. The basic idea of this study is to examine how accurate thetheoretical modeling can be for XPS and NEXAFS spectra of fullerene-based solar cellacceptors and to provide correct spectral assignments for these spectra. Six typicalmolecules,[6,6]-phenyl-Cn+1-butyric acid methylester (PCnBM)(n=60,70,84),[6,6]-thienyl-C61-butyric acid methyl ester (ThC60BM), bis(4-methoxyphenyl)-methano[60]-fullerene (DPM) and bis[6,6]-phenyl-C61-butyric acid methyl ester (bisPC60BM) have beencalculated, which reveal the specific structure-spectrum relationship. The calculated resultsare in perfect agreement with the available experimental spectra. On the foundation ofconventional building block (BB) approach, we have proposed a modified building block(MBB) approach to quickly resemble the total spectrum of the entire system by summing upthose from two small species. It will allow obtaining the NEXFAS spectra of the largenumber of fullerene-based solar cell acceptors available with very little computationaleffort.Rhodamine family is one kind of dye material with excellent properties of spectroscopy,which is often used to investigate the surface-enhanced Raman spectroscopy (SERS). Oneexperimental study shows that the Raman spectroscopy of Rhodamine B (RhB) molecule inaqueous solution is with much difference with the SERS spectrum on substrate, which is a disadvantage for studying SERS spectrum. In solution, the cation and anion of Rhodaminemolecules are separated, our result shows that the calculated Raman spectra of the cation ofRhodamine molecules, Rhodamine6G (R6G), Rhodamine123(Rh123) and Rhodamine Bin gas phase match the experimental spectrum in solution very well. We also studied thesolvent effect, but the solvent plays a dispensable role. For simulating the situation thatcation of Rhodamine B molecule is neutralized by any an electronegative paticle, thechlorine ion was used to form the neutral form of Rhodamine B molecule, as well as fourwater molecules to simulate the solvent. However, the Raman spectroscopy of neutral formalso has much difference with the SERS spectrum. It’s guessed that the geometric structureof Rhodamine B molecule gets a great change, which caused the difference of Ramanspectroscopy.This thesis consists of eight chapters as follows: The first chapter introduces thedevelopment of three kinds of organic functional molecular materials, as well as thespectroscopy technologies for study them. The second chapter, we have briefly introducedthe fundamental theories of quantum chemistry theory which are relevant to this thesis,especially the density functional theory (DFT), as well as the methods to study theproperties of molecule. In chapter three, the basic theory of X-ray spectroscopy is shown,especially the methods to calculate the X-ray photoelectron spectroscopy and near edgeX-ray absorption fine structure specstroscopy. Chapter four is the brief introduction ofRaman spectroscopy and the computional method to calculate the Raman spectroscopy. Inchapter five, we researched the effects of protonation, hydrogen bonding, andphotodamaging on X-ray spectroscopy of the amine terminal group in aminothiolatemonolayers. In chapter six, we show the study of core excitations of fullerene-basedpolymer solar cell acceptors. Chapter seven is the study of of solvent effect on Ramanspectra of Rhodamine molecules. The last chapter draws a conclusion for the whole work ofthis thesis, and gives a prospect on the development of theoretical study for organicfunctional molecular materials’ X-ray spectroscopy and Raman spectroscopy. |
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