Date of Award
Doctor of Philosophy
Our group designs and investigates photochromic organometallic systems that undergo a photo-induced, ultrafast linkage isomerization between two tethered functional groups and form thermally stable photochromes, which are required properties for optical data storage and image processing applications. These goals were approached by exploring (η5-pentalenyl)Mn(CO)3 complexes with coupled functional groups tethered on the saturated pentalene ring. Alternative synthetic approaches to the formation of functionalized (η5-pentalenyl)Mn(CO)3 complexes were performed with less expensive reagents than previously reported. A (η5-pentalenyl)Mn(CO)3 complex with a propargyloxy side chain, HpOCCH, shows a 32% increase in yield of chelate photo-products in comparison to the non-pentalenyl analog, CM-OCCH. However, time-resolved IR studies provide mechanistic evidence of chelation after solvent coordination or agostic interaction in the nanosecond timescale. A series of (η5-cyclopentadienyl)Mn(CO)3 derivatives containing a 2-pyridinyl group coupled to a variety of hydrazone groups, A9, A7, and A6 ((η5-C5H4R)Mn(CO)3, R = CH2C(NN(CH3)2)Py, CH2C(NNHPh)Py, CH2C(NNH2)Py, respectively, where Py = 2 pyridinyl) have been synthesized and characterized spectroscopically in addition to their phenyl analogs, A13, A8, A12, ((η5-C5H4R)Mn(CO)3, R = CH2C(NN(CH3)2)Ph, CH2C(NNHPh)Ph, CH2C(NNH2)Ph, respectively). Of the six hydrazone compounds, the two with a dimethylhydrazone group, A9 and A13, produce thermally stable chelates, while A9 displays photochromic properties. Quantum yields for the formation of photoproducts cA9py and cA9hy from A9 are 0.26 and 0.12, respectively, due to competing photon absorption by the sidechain. Irradiated A7, A6, and A8 produce unstable hydrazone chelates, which tautomerize to azo chelates while irradiated A12 forms a hydrazone chelate that decomposes. Time-resolved IR studies of the six hydrazones show ultrafast chelation with no evidence of transients. A series of (η5-cyclopentadienyl)Mn(CO)3 derivatives containing alkyne groups coupled with either a methylsulfide (S1-CCH and S1-OCCH) or 2-pyridinyl group (Py1 CCH and Py1-bisCCH) were also synthesized and characterized. UV irradiation of S1-CCH, S1-OCCH, Py1-CCH, and Py1-bisCCH produces stable chelates, but subsequent irradiation of methyl sulfide chelates at various wavelengths does not lead to isomerization.
dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.
Johnson, Jermaine O'Bryan, "Directions Toward the Design and Synthesis of Photochromic Organomanganese Systems Based on Ultrafast Linkage Isomerization" (2015). Electronic Theses and Dissertations. 1250.