Theoretical Studies On The Nonlinear Optical (NLO) Properties Of Fe(η～5-C₅₅X₅)₂ (X=CH, N, B) And Other Fullerene Derivatives

Since the discovery and bulk preparation of C60, the unique properties of fullerenes have attracted much attention of an increasing number of scientists. A fullerene is a fascinating molecule because it is a nanometer-sized cluster and has a large number of conjugated double bonds. These characteristics lead us to expect large nonlinear polarizabilities. But the third-order nonlinearity of the C60 and other high fullerenes are not as large as expected in the beginning both from experiments and from theory. However, chemically modified fullerene derivatives of charge transfer (CT) complex showed extremely large optical nonlinearity.In the present work, the geometry structures, electronic properties and nonlinear optical (NLO) properties of two kinds of fullerene derivatives have been investigated by quantum chemistry calculations. Our work has been focus on the following two aspects:1. Electronic spectrum, third-order polarizabilities, and origin of third-order nonlinear optical (NLO) properties of Fe(η5-C55X5)2 (X=CH, N, B) have first been investigated by using time-dependent density functional response theory. The three molecules have stable structures with D5h and D5d symmetry. We analyzed the interactions between Fe2+ and C55X5- ligand. The absorption spectrum of the systems indicated that the shorter-wavelength transitions are ascribed toπ-π* excitation of the C50 moiety mixed with charge transfer transition of ferrocene itself, and the longer-wavelength transitions are ascribed to the unique charge transfer transition from ferrocene to C50 moiety of these systems. The calculated third-order polarizabilitiesγvalues shown that this class of fullerene-ferrocene-fullerene hybrid molecules possesses a remarkably large third-order NLO response, especially for D5d-Fe(η5-C55B5)2 with the static third-order polarizability (γav) -10410×10-36esu. Thus, these complexes are potential to be excellent third-order nonlinear optical materials. The major contributions to theγav value suggested that the charge transfer from ferrocene to C50 moiety along the z-axis play the key role in the NLO response of Fe(η5-C55X5)2 (X=CH, N, B). Furthermore, boron substitution is more important in enhancing the optical nonlinearity, owing its better conjugation characteristic concluded by Density-of-States analysis.2. We present a quantum-chemical analysis of zinc porphyrin-C60 pair with strong electronic communication through hydrogen bond to provide insight into the intermolecular interactions and the relationship between its structural and non-linear optical propertiy. Porphyrin amidine and fulleropyrrolidine carboxylic have been used to construct electron donor-acceptor (D-A) dyad through the formation of amidinium-carboxylate salt bridges which consist of complementary double hydrogen bonds. The hydrogen bond lengths of O―H…N and N―H…O in above compound are 1.447? and 1.486? respectively and these values are in the range of strong hydrogen bond. The calculated binding energy of double hydrogen bonds is 539.09 KJ/mol. The absorption spectra of zinc porphyrin-C60 dyad obtained from TDDFT calculation shown that the increasing transitions from benzene moiety to fullerene moiety. The static second-order polarizability is much larger than porphyrin amidine and fulleropyrrolidine carboxylic.