Density Functional Theory Calculations on η5-Monocyclopentadienylmetal Complexes with Conjugated Nitrile Chromophores

During the past decade, the interest on organometallic compounds for the development of novel nonlinear optical (NLO) materials with large second-order nonlinearities has considerably increased in view of their potential application in the area of integrated optics [1]. Experimental and computational investigations utilizing quantum theory afforded useful insights concerning the molecular structural requirements necessary to induce large second-order nonlinearity response. The strategy to obtain these properties has been the synthesis of compounds with highly polarizable asymmetric structures through the existence of delocalized electronic system bridge (chromophore) between an electron-withdrawing and electron-donating group. Recent experimental work on 5-monocyclopentadienylmetal complexes with p-substituted benzonitrile and oligothiophene nitrile chromophores showed a correlation between the first hyperpolarizability () and the communicability between the chromophores and the organometallic fragments [2]. In addition, some EHMO calculations on nickel and iron complexes had corroborated that the larger values of experimental hyperpolarizability correspond to lower HOMO-LUMO gaps [3]. In order to get a better understanding on the electronic factors that may be responsible for the second-order nonlinear optical behavior of [CoCp(dppe)(p-NCC6H4R)]2+ and [FeCp(dppe)(NC{SC4H2}nNO2)]+ complexes and their correlation with experimental spectroscopic and electrochemical data, density functional theory calculations were made in the model complexes [CoCp(H2PCH2CH2PH2)(p-NCC6H4R)]2+ and [FeCp(H2PCH2CH2PH2) (NC{SC4H2}nNO2)]+ (n=1,2). Especial emphasis was given to the HOMO-LUMO gaps and their character. Spatial localization of electron charge by means of topological analysis of the electron localization function (ELF) as been performed to gain insight into the nature of the chromophores binding to the metal centers

Nonlinear Optical Properties of η5-Monocyclopentadienyliron Complexes From DFT Calculations

Recently, organometallic complexes have emerged as potential building blocks for second-order nonlinear optical (SONLO) materials in view of their potential application in the area of integrated optics [1]. Unlike organic molecules, whose optical nonlinearities have been extensively studied by computational methodologies using both semi-empirical and ab initio methods, organometallic systems have received much less attention due to the difficulty in the calculation of reliable hyperpolarizabilities in the presence of transition metal atoms. ZINDO has been the most widely used program to calculate SONLO coefficients of organometallic compounds. A more reliable approach, using the density functional theory (DFT) method is less explored but has been increased in the recent years. Experimental work on 5-monocyclopentadienyliron complexes with p-nitro benzonitrile ligands showed that the first hyperpolarizability decreases with increasing conjugation length of the chromophores [2]. EHMO calculations performed on model complexes [FeCp(PH3)2(p-NCR)]+ confirms this behavior and showed that the larger values of experimental hyperpolarizabilities correspond to lower HOMO-LUMO gaps [3]. For similar complexes possessing a thiophene based conjugated backbone, a dramatic increase in experimental first hyperpolarizability with increasing conjugation length was observed [4]. The explanation of this different behaviour was not definitively established. In order to get a better understanding on the electronic factors that may be responsible for the SONLO behavior of these compounds and their correlation with experimental spectroscopic and electrochemical data, high accuracy DFT calculations using GAMESS-US were made in model complexes [FeCp(H2PCH2CH2PH2)(NC{SC4H2}nNO2)]+ (n=1-3). Spatial localization of electron charge as been performed to gain insight into the nature of the chromophores binding to the metal center. First static hyperpolarizability was calculated, compared with experimental results and correlated to the HOMO-LUMO gaps

Density Functional Theory Calculations on Monocyclopentadienylnitrilecobalt Complexes Concerning Their Second-order Nonlinear Optical Properties

Density functional theory calculations were performed to determine first static hyperpolarizabilities (β) of model complexes [CoCp(H2PCH2CH2PH2)(p-NCC6H4R)]2+. The results show that these complexes have low hyperpolarizabilities which are due to weak electronic coupling between the organometallic fragment and the nitrile ligands. It was shown that in these complexes the electronic excitation responsible for second-order non-linear optical response is a ligand to metal charge transfer. The results also show the inverse relationship between the first hyperpolarizability and the corresponding electronic transfer energy gaps