Lanthanide (III) complexes are used extensively in solar conversion devices, such as Luminescent Solar Concentrators (LSCs) and Luminescent Down-Shifting (LDS) for their peculiar characteristics of narrow band emission, avoidance of re-absorption losses due to large Stokes shift and possibility of high photoluminescence quantum yield (PLQY). The study has looked into the synthesis of Ln (III) complexes of the general formula: [Ln(hfac)3DPEPO], where DPEPO = bis(2-(diphenylphosphino)phenyl)ether oxide, and hfac = hexafluoroacetylacetonate. The work presented in this thesis focuses on the synthesis, and subsequent photophysical characterisation of these Ln(III) complexes, plus characterisation and spectroscopic study of [Tb(pobz)3(hacim)2], (where Hpobz = phenoxybenzoic acid, and Hacim = acetylacetone imine), yielding results that open new design of functional Ln(III) systems. Spectroscopic study of Chromium dioxalate and analogous compounds has revealed that with the appropriate design, Cr(III)Ln(III) energy transfer can be achieved, while study of polyaromatic hydrocarbons (PAH) such as coronene, enable to explore a ligand with better absorption in the whole UV region. These results open attractive perspectives for light-conversion systems, such as LSC devices.

Small clusters of [6,6] phenyl-C61-butyric acid methyl ester (PCBM) molecules are analyzed with respect to their equilibrium geometries and associated electronic as well as energetic properties. Plane wave density functional theory (PWDFT) computations, assisted by molecular dynamics (MD) simulations, are performed on systems of the form PCBMn (n = 1-5). The bonding operative in these units is described as a cooperation between HO bonding, involving the C5H9O2 groups of the PCBM molecule, and fullerene-fullerene attraction. The maximally stable structures identified tend to include a dimer motif that combines both interaction modes. The great importance of van-der-Waals effects in stabilizing the studied clusters is demonstrated by comparing the PCBM3 series with and without inclusion of a van-der-Waals term in the PWDFT procedure. The two approaches yield reverse orders of stability. A decreasing tendency in the Kohn-Sham HOMO-LUMO gaps of PCBMn with the cluster size may be used to monitor PCBM aggregation in the active layer of organic photovoltaic devices by optical spectroscopy.