Zn (II) and Cu (II) Halide Complexes of Poly(propylene amine) Dendrimer Analysed by Infrared and Raman Spectroscopies

Two nondestructive and complementary spectral methods as infrared and Raman spectroscopies have been used for characterizations of poly(propylene amine) dendrimers comprising 1,8-naphthalimide units in the dendrimer periphery and their metal complexes with Cu2+ at Zn2+ ions. 1. Introduction Poly(propylene amine) (PPA) is a new class of commercial dendrimers possessing tertiary amino groups in the core and terminal primary amino groups in the dendrimer periphery [1]. Their luminescent characteristics can be customized by modifying the periphery with different fluorophores. We have extensively studied the dendrimer modifications with 1,8-naphthalimides in response to the needs of vanguard sensors for preventing environment pollution [2–7]. Different spectral methods and techniques as UV-vis and fluorescence, FTIR and Raman, NMR, AFM, and EPR are used for identification and characterization of dendrimers [8]. Some of these methods used for studying the vibrations of atoms in dendrimer molecules are infrared and Raman spectroscopies. The difference between both of spectral methods lies in the fact that while in infrared spectroscopy are important oscillations, changing dipole moment, in the Raman spectroscopy is characteristic the change of polarizability of molecules. The main advantage of Raman spectroscopy compared to Infrared spectroscopy is the small water absorption, which is offered especially for biological and medical investigations without further sample preparations. Surface-enhanced Raman spectroscopy (SERS) takes the advantage of strongly increased Raman scattering signal generated by local field enhancement near metallic nanostructures [9]. An example exploits the local plasmon modes at the interface between two metal nanoparticles. A key requirement to achieve such detection is the placement of the analyte close to more than one plasmonic surface [10]. To date, isotropic and anisotropic metallic nanoparticles such as gold and silver have been promising SERS substrates because of their tunable optical properties, controllable particle size distribution, easy synthesis procedure, long-term stability, and high biocompatibility [11]. On the other hand, the infrared spectroscopy is more informative in the case of the investigations of polar functional groups in organic compounds. This means that these spectral methods are complementary and appropriate for researching the structure of organic molecules [12]. In this paper we present Raman and infrared spectral analyses on Zn (II) and Cu (II) halide complexes of poly(propylene amine) dendrimers of