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 Title: Porphyrins as second order nonlinear optical materials Author(s): Chou, Homer Doctoral Committee Chair(s): Kenneth S. Suslick Department / Program: Chemistry Discipline: Chemistry Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Chemistry, Inorganic Chemistry, Organic Chemistry, Physical Physics, Optics Engineering, Materials Science Abstract: Because of the unusually high thermal and chemical stability of porphyrins as well as their very large $\pi$-conjugated systems, three classes of high $\beta$-value push-pull porphyrins were synthesized and subsequently successfully engineered into Langmuir-Blodgett (LB) films for a systematic evaluation of porphyrins as $\chi\sp{(2)}$ materials. Class I explored the effects of the number of donor-acceptor groups on the porphyrin periphery (i.e., H$\rm\sb2(an\sb3P), H\sb2$(cis-a$\rm\sb2n\sb2$P), H$\rm\sb2(a\sb3$nP), H$\rm\sb2(a\sb4$P) where a = 4-(N-octadecylamido)phenyl or 4-(N-octadecyl-amino)phenyl; n = 4-nitrophenyl; P = 5,10,15,20 substituted tetraarylporphyrinate (2-).). Class II examined the effect of varying the strength of cis-substituted donor-acceptor pairs on the porphyrin periphery (i.e., H$\sb2$(cis-a$\rm\sb2n\sb2$P), H$\sb2$(cis-c$\rm\sb2p\sb2$P), and H$\sb2$(cis-h$\rm\sb2py\sb2$P) where c = 4-(2-cholesteryloxy)-ethoxyphenyl; h = 4-hydroxyphenyl or 4-methoxyphenyl; and py = 4-pyridyl or 4-(N-octadecyl) pyridiniumyl). Class III looked at the respone of a heterosubstituted bis- push-pull cerium sandwich porphyrin complex, (Ce$\rm\sp{IV}$(TPyP)(TMeP)) $\sp{4+}$I$\sb4$ (where Py = 4-(N-octadecyl)pyridiniumyl and Me = 4-methoxyphenyl). Characterization of the porphyrin LB films reveals rather surprising behavior. The isotherm data show that the mean molecular area of the porphyrins increase smoothly from 80-200A as the number of aliphatic chains increase around the porphyrin periphery from one to four. In addition, based on UV-visible linear dichroism, all of the porphyrin films possess C$\rm\sb{\infty v}$ symmetry and adopt a tilt angle, $\theta$, of about 33$\sp\circ$ with respect to the fused quartz substrate. The proposed fixed orientation model suggests that the interporphyrin $\pi$-$\pi$ interactions dominate the porphyrin orientation while the number of aliphatic chains around the porphyrin periphery determines the porphyrin's packing density in the LB film. After these monolayers were transferred to fused quartz substrates, the $\chi\sp{(2)}$ response of these transferred porphyrin monolayers was measured both at $\lambda$ = 1064 and 1906 nm. The resonance-enhanced $\chi\sp{(2)}$ response at 1064 nm showed that the best films (i.e., H$\sb2$(cis-a$\rm\sb2n\sb2$P)) showed an extraordinarily high $\chi\sp{(2)}$ response of 1.3 $\times$ 10$\sp{-6}$ esu. At 1906 nm, these same films showed a $\chi\sp{(2)}$ response of similar to that of other inorganic and organic compounds of 2.6 $\times10\sp{-8}$ esu. Issue Date: 1995 Type: Text Language: English URI: http://hdl.handle.net/2142/23390 Rights Information: Copyright 1995 Chou, Homer Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9624315 OCLC Identifier: (UMI)AAI9624315
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