| Recent years, novel two-photon absorption (TPA) materials have attractedincreasing interest due to their potential applications in many different fieldssuch as chemistry, physics and biology. Up to now, the practical TPA materialsare still limited, so further exploring and researching on new materials withpotential TPA properties are urgent. In this thesis, systematic investigation onseries of macrocyclic thiophene-based organic TPA materials have beenimplemented in theory. Density functional theory (DFT) was used to optimizegeometrical structures. On the basis of the equilibrium geometries, one-photonabsorption properties have been calculated by TDDFT and ZINDO methods,and then transition energies and transition moments were obtained, finally, therelational information on one-and two-photon absorption properties wascalculated combining SOS equation and self-compiled FTRNLO program. Theinternal relations between structure of macrocyclic thiophene-based moleculesand one-and two-photon absorption properties have been revealed. Theseinvestigations will provide some useful and valuable information for designingand synthesizing novel TPA materials with large TPA cross-section values. Themain conclusions are shown as follows:1. Theoretical investigation on nonlinear optical properties of macrocyclicthiophene-based compounds C[3TDA]n(n=2–5, R=Bu)The geometrical structure, electronic structure, one-and two-photonabsorption properties of a series of macrocyclic thiophene derivativesC[3TDA]n(n=2–5, R=Bu) have been studied using DFT and ZINDO methodstheoretically. The results show that the range of λ1maxs is390–470nm and thatof λ2maxs is640–670nm, while, both λ1maxand λ2maxgradually enlarge asincreasing the number of the C[3TDA] unit, and the value of δmaxincreases inturm, exhibiting larger δmax. The factors influencing on the value of δmaxwereanalyzed in detail, indicating that transition dipole moments M0kand Mknplayimportant roles on δmax. Both π-electron number (Ne) and the product ofoscillator strengths (∫0k×∫kn) are in proportion to δmax. Besides, the values of thestatic second-order nonlinear optical susceptibilities (β0) calculated by ZINDO-SOS and FF methods show the same changing trend, i.e. the absolutevalue of β0increases as the unit number increases. The value of β0predicted byZINDO-SOS method is an order of magnitude larger than that by FF method.Moreover, δmaxlinearly depends on β0.2. Theoretical study on one-and two-photon absorption properties ofmacrocyclic thiophene-based compounds with the electron donor (–NH2) andacceptor (–CN) groups C[3TDA]n(n=2–5, R=NH2, CN)The geometrical and electronic structures, and one-and two-photonabsorption properties of C[3TDA]n(n=2–5, R=NH2, CN) were investigated. Itshows λ1maxs of the designed molecules with D or A substituents exhibitred-shift compared with molecule SⅡ. And δmaxvalues increase with increasingthe number of D/A pair. The δmaxvalues of D–A type of molecules are close tothat of A–A, and larger than that of D–D and SⅡ molecules. The moleculesshow larger δmaxwhen electron donor and acceptor located on the opposite site(14:58), which is ascribed to the enhancement of the ICT between D and A. It isfurther confirmed that macrocyclic thiophenes with stronger D/A substitutionhave larger δmaxthrough analyzing the charge change (△Q) of substituent andring skeleton. In addition, other important factors influencing the value of δmaxwere analyzed, the resultes indicate that the values of M0kfor D–A and A–Amolecules are larger. And△μ0nof D–A type of molecule is larger than that ofother two types (A–A and D–D), which will result in their larger δmax. BesidesM0kand Mknhave played important roles on the increase of δmax,0k×knis indirect proportion to δmax. In summary, the present computational results providea useful guideline for the design of novel D–π–A molecules with large δmaxbyenlarging the strength, increasing the number and changing the position of Dand A substituents based on the circular π-conjugated skeleton. All abovesuggest this series of macrocyclic thiophene-based derivatives are expected tobe promising two-photon absorption materials.3. Theoretical study on linear and nonlinear optical properties ofmacrocyclic thiophene derivatives with different connecting π-conjugatedbridge and ring sizeThis contribution reports the geometries, electronic structures, linear andnonlinear optical properties of a series of macrocyclic thiophene derivatives with different connecting bridge and ring size in theory. It provides themolecules have stronger OPA peak in the wavelength of406.7–541.9nm, andexhibit transparent in the wide range of UV-vis wavelength. Both OPAand TPA peaks shift red as Ne increases and in different windows that don'tsuperpose on each other. The values of δ(1)maxand δ2maxenlarge with increasingNe, the largest values of δ2maxfor C[6TAE]3–Me and C[6TAE]3observedat long wavelength is20and23times larger than that of the unit molecules,respectively. The relationship between molecular structure and microscopicphysical quantity impacting on the value of δ2maxwas investigated, indicatingthat different connecting bridge and ring size have mainly enhanced M0kandMkn, and increased∫0k×∫knand Ne to some extent, which have played importantroles on the increase of δ2max. In addition, ICT impacting on the value of δ2maxwas analyzed combined with the value of△Q. The macrocyclic thiophenederivatives C[3TDA]4,C[12TA], C[6TAE]2and C[6TAE]3(R=Bu) havelarge negative value of Reγ, besides have large value of Imγ, indicating thisseries of molecules can be used as two-photon self-defocusing optical powerlimiting materials.
|
PDF Full Text Request