Synthesis And Photophysical Properties Of Axial-Bonding Type Phosphorus (V) Porphyrins

Because of their outstanding photophysical and redox properties, porphyrins have been widely used as building blocks in the construction ofπ-conjugated systems for their potential applications in molecular electronics, photochemical energy conversion and storage, switches, etc. Nevertheless most of these porphyrins reported so far are modified by the functional substitutes in the peripheral meso- orβ- position via covalent linkages. The"axialbonding"strategy barely appears to be reported. The [P(TPP)Cl2]Cl is a well-known axialbonding building block, which prefer to take place nucleophilic substitution reaction with phenols and alcohols. On the other hand, if the donor is modified at axial position of phosphorus (V) porphyrins, which are strong electron acceptors, it might lead to novel materials with fascinating photo- and electrophysical properties.In the second chapter, we utilized convergent method in synthesizing monodisperse dendritic carbazoles of 1st to 3rd generation. As the 3,6-positions of carbazole are active, t-butyl groups were introduced into the 3,6-positions of the peripheral carbazoles in the dendrons not only to promote the stability but also to increase the electron-donating ability. Meanwhile, the introduction of t-butly may improve their solubility. We utilized Ullmann condensation reaction and the cleavage of the N-Ts bond to synthesize monodisperse dendritic carbazoles with hydroxyl group. Then, the dendritic carbazoles was selected as axial substitutions in Phosphorus (V) Porphyrins. Thus, a donor-acceptor system based on phosphorus (V) porphyrins, in which the photoinduced electron transfer could be happened, was gained. The photophysical properties of target molecules revealed that these molecules did not emit fluorescence under UV light. We presumed that it may arouse from the intramolecular electron transfer, and we prepared three layer film photovoltaic devices based on the target molecules. Notably, a photovoltaic response to the visible light is observed in the incident photon to current conversion efficiencies (IPCE) spectra. This result demonstrated that the intramolecular electronic transfer did occur. It was found that the 2nd generation dendrimer exhibited the strongest photovoltaic response among these three dendrimer molecules. This D-A-D type monodisperse dendritic carbazoles may lead to potential applications as photovoltaic materials in solar cells.In the third chapter, we synthesized novel D-A type molecules, in which the triphenylamine was used as an electronic donor and phosphorus (V) porphyrins as an acceptor. The donor and acceptor moieties were linked by saturated carbon chains with different length. Because the activity of phenol and alcohol is different in compound 5, 6 and 7, the synthetic conditions were investigated. The emission fluorescence spectra of compounds 5, 6 and 7 showed that in the same solvent the emission fluorescence intensity increased with the increasing length of the saturated carbon, indicating that the spacer had effect on the electronic transfer. On the other hand, the emission fluorescence intensity of the phosphorus (V) porphyrins decreased with the enlargement of the solvent polarity. This result can be explained that the larger is the solvent polarity, the stronger is the effect on the charge separation state. Therefore, the intramolecular electronic transfer can be tuned by adjusting the spacer between donor and acceptor and solvent polarity.