Chapter one begins with a theoretical description of the electronic structure of the various compounds studied in this thesis, which includes group VI Fischer carbenes, ferrocene and meso-substituted porphyrins. This is followed by an introduction to the principles of photophysics and non-lmear optics. Chapter one finishes with an outline of the experimental techniques of laser flash photolysis and electric field induced second harmonic generation (EFISHG). Chapter two opens with a literature survey of the photochemistry of Fischer carbene complexes covering the areas of photoinduced CO loss, syn-anti isomerisation and ketene formation. The synthesis of some ferrocenyl chromium and tungsten methoxy Fischer carbene complexes, (CO)5M=C(OMe)Fc and l,r-[(CO)5M=C(OMe)]2Fc (M = Cr, W), is then presented and their photochemistry is investigated m cyclohexane using the techniques of steady state and laser flash photolysis Electrochemical, X-ray crystallographic and EFISHG data are also presented. An investigation into the photochemistry of some additional ferrocenyl. Fischer carbene complexes containing a vmyl spacer is presented in chapter three Photoinduced CO loss of the complexes (CO)5M=C(OMe)C2H2Fc and (CO)sM=C(Pyrrolidine)C2H2FC (M = Cr, W) is investigated in cyclohexane using the techniques of steady state and laser flash photolysis. The results of photoinduced cistrans isomerisation of the complexes (CO)5M=C(OMe)C2H2Fc and (CO)5M=C(OMe)C2H2Ph (M = Cr, W) are also discussed Electrochemical, X-ray crystallographic and EFISHG data are also included. Chapter four contains a literature survey of the synthetic techniques for the synthesis of meso-substituted porphyrin compounds covering the development of the area from the early methods of Rothemund and Adler to the modern stepwise techniques of Lindsey et al. The experimental details for the synthesis of some novel thienyl and ferrocenyl porphyrins are reported and their methods discussed. A photophysical investigation of some novel meso-substituted thienyl porphyrins is presented in chapter 5 using the techniques of electronic absorption spectroscopy, fluorescence spectroscopy, laser flash photolysis, time correlated single photon counting and cyclic voltammetry. These novel meso-substituted thienyl porphyrins show some characteristic photophysical properties in contrast to conventional mesosubstituted tetra-aryl porphyrins and may find interesting applications in non-lmear optical materials and other photonic devices. Chapter six opens with a literature survey of ferrocenyl porphyrins followed by an investigation into the photophysical properties of some novel meso-substituted ferrocenyl/ferrocenmm porphyrins using the techniques of fluorescence spectroscopy, spectro-electrochemistry, laser flash photolysis, time correlated single photon counting and cyclic voltammetry. Efficient quenching of the porphyrin luminescence was observed due to the appended ferrocenyl moiety, which acts as an electron-donor and quenches the Si, S2 and Tt excited states of the porphyrins by an electron-transfer mechanism. On decreasing the electron-transfer efficiency of the iron centre by oxidising the ferrocene moiety to the ferrocemum ion the luminescent properties of the porphyrin ring are switched on again. Finally chapter seven discusses future work for chapters 2,3,5 and 6. Also the synthesis and properties of some novel thiophene ligands and their ruthenium complexes are presented and their potential applications as non-lmear optical materials for second and third harmonic generation are discussed. The overall aim of this thesis was to study the photochemistry/photophysics of organometallic donor-acceptor compounds, which incorporated the Fischer carbene unit as an acceptor moiety Ferrocene and porphyrin units were chosen as the donor moieties. The synthesis of porphyrin systems containing the Fischer carbene acceptor group was unsuccessful.