Theoretical Investigation On The Magnetic Properties Of Highly Conjugated Macrocycles Molecules And Organic Light Emitting Materials Which Containing Thiophene Moiety

Aromaticity has been used in chemical literature frequently. But so far, there isno precise definition to explain what the aromaticity really is. Aromaticity hasprovided one of the most fruitful interplays between theory and experiment.Aromaticity is related to the stability of molecules. It is very important to investigatethe aromaticity of molecules. We try to make the molecules from aromaticity toantiaromaticity by changing the structures of molecules. A series of highly conjugatedmacrocycles, they all have four pyrroles, but the linkage bridge of them is different.We predict the aromaticity, stability and phtophysical behavior are different. We usethe properties of oligomers to calculate the properties of polymers by extrapolationapproach.The paper is divided into six chapters. In chapter1, we summarize thedevelopment history of the concept of aromaticity, the quantitative standard ofaromaticity and organic light emitting masteries. In Chapter2, an overview oftheoretical methods including molecular orbital theory,configuration interactiontheory, perturbation theory,density functional theory,electronic excited state theory,thechoice of basis set,electronic spectrum and analysis method of intermolecular weakinteraction. From chapter3to chapter5, theoretical analysis on magnetic properties ofa series of highly conjugated macrocycle molecules. In chapter6, theoretical studieson the electronic structures and optical properties of the thiophene oligomers, we predict the properties of polymers by extrapolation method. We calculated the chainlength and end-caps affect the optical properties of molecules.1. We have theoretically investigated the magnetic properties of N-confusedporphyrin (NCP), tetraphenyl-N-confused porphyrin (TPNCP) and their substitutedderivatives with O, S and Se heteroatoms (2ONCP,2STPNCP,2SeNCP,2OTPNCP,etc.) by using DFT method. In the minimum energy structures of the2OTPNCP, thetwo couples opposite phenyl substitutes are staggered. In the case of TPNCP,2STPNCP and2SeTPNCP, two phenyls being respectively close to or opposite toN-confused pyrrole are found to be pointed the same direction, whilst others are in theopposite direction. Based on the equilibrium structures, the1H chemical shifts andnucleus-independent chemical shifts (NICS) are calculated in this paper. The π currentdensity being induced by the tridimensional perpendicular magnetic field transmitsthe inner section of the pyrrole segments for NCP and TPNCP. As for theirsubstituted derivatives with O, S and Se atoms, the current path passes through theouter section of the two heterorings. The NICS values at the ring critical points of theheterorings are much lower (in absolute value) than those of which is at the center ofan isolated pyrrole molecule. The1H NMR for β H atoms of the heterorings decreasesfrom O, S to with Se.2. Theoretical study about the magnetic properties of conjugated organicmolecules containing borepin with π current density has also been carried out in thispaper.1-(2,4,6-trimethylphenyl) borepin moiety is centered and other differentgroups are situated on the both β sides, which are named1-12as theoretical model inorder to establish the relationship between aromaticity and geometry variation ofborepin. The optimized molecular structures of1-12are almost keeping planar and theC2-C3bond length of borepin turns longer from1to12. Different borepin-annulatedring could change the conjugated effect of π-electron between borepin and theseborepin-annulated rings. Moreover, when the C2-C3bond length of borepin extendedthan ca.1.417, the molecule presents antiaromaticity, in other words, the moleculebecame unstable. But the β position fragment and substituent groups of borepin are not affected in this case, they are still steady. But the central borepin ring current iscounteracted by symmetrical overlap with affiliated borepin-annulated ring current.Hence, the central borepin ring breaking would be liable to occur. These moleculeshave higher vertical ionization potentials (VIPs) and lower vertical electron affinities(VEAs), which suggest that these molecules could easily exist in anionic form.3. We have designed a series of highly conjugated macrocycles containing fourpyrroles with the different linkage of bridges, which are named four pyrrole (Pf),methylene-dipyrrolidine (Pm), porphyrin (Pr), porphycene (Pc)[22]porphyrin-(2.2.2.2)(P [22]), as the theoretical model in order to investigate thestability, aromaticity, photophysical behavior and the influence of getting or losingelectron to the neutral molecule. The geometric structures of the molecules areoptimized by density functional theory method with6-31G (d) basis set. Theabsorptions are calculated by the time-dependent density functional theory method(TD-DFT). Based on the optimized structures, the nucleus-independent chemicalshifts (NICS) are calculated. The molecular with negative NICS value possesseslarger HOMO-LUMO gap than that with positive NICS value, the molecular withbigger positive NICS value possesses smaller HOMO-LUMO gap, the molecular withbigger negative NICS value (in absolute value) possesses bigger HOMO-LUMO gap.The current density indicates that π-electron delocalization is more effective in Pm2-,Pr, Pc2-and P[22]1-Pm than Pm1-, Pm1+, Pr2-, Pr1-, Pr1+, Pc, Pc1-, Pc1+, P[22],P[22]2-and P[22]1+, and is corresponding to the stability of molecules. Theabsorptions of the molecules are all in the UV-visible and infrared region. The majortransitions for most of the molecules are all from HOMO to LUMO. Compared to Pf2-,Pm2-, Pr2-, Pc2-and P[22]2-, Pm2-shows distinctive photophysical properties, which isdue to reduced HOMO-LUMO gap, structural distortion and strong antiaromaticity.4. Structural, electronic, and optical properties of a series of π-conjugatedthiophene oligomers P1-P3and CF3P1-CF3P3have been theoretically investigated.P1-P3contain the2-(trifluoromethyl) thieno [3,4-b] thiophene moiety as the centreand1–3repeating thiophene units adjacent to its two sides respectively, while their corresponding derivatives CF3P1-CF3P3with the CF3as end-caps. The geometricstructures of the oligomers in the ground and excited state were optimized byPBE1PBE and CIS methods with6–31G (d) basis sets, respectively. All the oligomersexhibit zigzag arrangements. The absorptions and emissions were calculated by thetime-dependent density functional theory method (TD-PBE1PBE). The lowest-lyingabsorptions of all the oligomers can be characterized as π-π*electron transition. Foreach series of oligomers, there is a progressive lowering in HOMO-LUMO gap withthe increase of the repeating unit, being consistent with the red-shifted trend in thelowest-lying absorption and fluorescence from P1to P3and CF3P1to CF3P3. Tocompare the P-and corresponding CF3P-oligomers, the end-cap CF3group causes theslight blue shifts in absorption and emission spectra. The ionization potentials (IPS),electron affinities (EAs), and reorganization energies (λ) as well as the hole/electronextraction energies (HEP/EEP) of the oligomers were explored and those of thecorresponding polymer were obtained by extrapolation method. The IP and HEP ofP-polymer are lower than those of CF3P-polymer, indicating that the P-polymer ismore suitable for hole transport than CF3P-polymer, while the higher EA and EEP forCF3P-polymer suggest the better electron transfer property. For CF3end-caps, theCF3P-polymer exhibits the equal reorganization energy between electron and hole,which is a precondition for the charge transfer balance.