@article{geier_ciringh_li_haynes_lindsey_2000, title={A survey of acid catalysts for use in two-step, one-flask syntheses of meso-substituted porphyrinic macrocycles}, volume={2}, ISSN={["1523-7060"]}, DOI={10.1021/ol005917h}, abstractNote={[reaction: see text] Diverse Lewis acids and Bronsted acids were examined in the two-step, one-flask synthesis of meso-tetraphenylporphyrin, N-confused tetraphenylporphyrin, and tetraphenylsapphyrin. The scope of acid catalysis was found to be very broad, with 35 of 45 acids providing TPP in yields ranging from 5% to 58%. NC-TPP was also widely observed in yields of 1-40%, and TPS was infrequently observed in yields of <1%. Additionally, conditions were found for direct preparation of magnesium TPP and copper TPP.}, number={12}, journal={ORGANIC LETTERS}, author={Geier, GR and Ciringh, Y and Li, FR and Haynes, DM and Lindsey, JS}, year={2000}, month={Jun}, pages={1745–1748} }
 @article{wagner_li_du_lindsey_1999, title={Investigation of cocatalysis conditions using an automated microscale multireactor workstation: Synthesis of meso-tetramesitylporphypin}, volume={3}, ISSN={["1083-6160"]}, DOI={10.1021/op9800459}, abstractNote={Prior manual work has shown that the condensation of mesitaldehyde and pyrrole leading to tetramesitylporphyrin depends sensitively on concentration and requires cocatalysis involving BF3·O(Et)2 and ethanol or other protic species. We have applied an automated microscale chemistry workstation capable of parallel or adaptive experimentation to systematically investigate these cocatalysis conditions. Examination of experimental grids spanning a 1000-fold range of the concentrations of BF3·O(Et)2 and ethanol identified the best cocatalysis conditions for various mesitaldehyde and pyrrole concentrations. As the reaction concentration increased from 10 to 200 mM, the optimal yields were achieved with a parallel increase in BF3·O(Et)2 concentration (from 3.3 to 56 mM), but the amount of ethanol remained relatively constant. Catalysis conditions were identified that afforded ∼30% yields for reactants in the range of 10−73 mM, thereby enabling the reaction to be performed at increased concentration without loss i...}, number={1}, journal={ORGANIC PROCESS RESEARCH & DEVELOPMENT}, author={Wagner, RW and Li, FR and Du, H and Lindsey, JS}, year={1999}, pages={28–37} }
 @article{li_yang_ciringh_seth_martin_singh_kim_birge_bocian_holten_et al._1998, title={Design, synthesis, and photodynamics of light-harvesting arrays comprised of a porphyrin and one, two, or eight boron-dipyrrin accessory pigments}, volume={120}, ISSN={["0002-7863"]}, DOI={10.1021/ja9812047}, abstractNote={Light-harvesting arrays containing one, two, or eight boron-dipyrrin (BDPY) pigments and one porphyrin (free base or Zn chelate) have been synthesized using a modular building block approach. The reaction of pyrrole and 4-(BDPY)benzaldehyde or 3,5-bis(BDPY)benzaldehyde, prepared by Pd-mediated ethynylation with the corresponding iodo-benzaldehydes, affords the desired BDPY-porphyrin array in yields of 10−58%. The arrays are soluble in organic solvents and have been characterized by static and time-resolved absorption and fluorescence spectroscopy. The blue-green BDPY absorption complements spectral coverage of the porphyrin chromophores and rivals the intensity of the porphyrin Soret band when eight BDPY accessory pigments are present. Efficient energy transfer from the BDPY pigment(s) to the porphyrin (free base or Zn-chelate) is observed in arrays containing one or two (>90%) or eight (>85%) accessory pigments per porphyrin. Biphasic excited-state decay behavior is exhibited by the BDPY pigments in isol...}, number={39}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Li, FR and Yang, SI and Ciringh, YZ and Seth, J and Martin, CH and Singh, DL and Kim, DH and Birge, RR and Bocian, DF and Holten, D and et al.}, year={1998}, month={Oct}, pages={10001–10017} }
 @article{ravikanth_strachan_li_lindsey_1998, title={Trans-substituted porphyrin building blocks bearing iodo and ethynyl groups for applications in bioorganic and materials chemistry}, volume={54}, ISSN={["0040-4020"]}, DOI={10.1016/S0040-4020(98)00408-6}, abstractNote={The modular synthesis of linear or cyclic multiporphyrin arrays relies on the availability of trans-substituted porphyrin building blocks with high solubility in organic solvents. Eleven porphyrin building blocks were synthesized bearing iodo, ethynyl, and 2-(trimethylsilyl)ethynyl groups at the 4-, 3-, or 3,5-positions of two meso-aryl units, and mesityl groups at the other two meso-positions. The synthesis involves condensation of 5-mesityldipyrromethane with one or two aryl aldehydes. Combinations of functional groups include di-iodo, tetra-iodo, bis[(2-(trimethylsilyl)ethynyl], iodo and 2-(trimethylsilyl)ethynyl, and ethynyl and 2-(trimethylsilyl)ethynyl. In addition, a porphyrin bearing one 4-iodophenyl group and one 3,5-bis(boron-dipyrrin)phenyl group was synthesized for applications in molecular photonic devices. The iodo and ethynyl groups are ideally-suited for Pd-mediated coupling reactions, allowing the porphyrin building blocks to be joined in the systematic construction of soluble multiporphyrin arrays.}, number={27}, journal={TETRAHEDRON}, author={Ravikanth, M and Strachan, JP and Li, FR and Lindsey, JS}, year={1998}, month={Jul}, pages={7721–7734} }
 @article{li_yang_tyhonas_maccrum_lindsey_1997, title={Beneficial effects of salts on an acid-catalyzed condensation leading to porphyrin formation}, volume={53}, ISSN={["0040-4020"]}, DOI={10.1016/S0040-4020(97)00770-9}, abstractNote={Addition of one of a variety of salts to the room temperature, two-step, one flask reaction at 0.1 M forming tetraphenylporphyrin (TPP) gave yield increases of up to 2-fold. Among 21 insoluble salts, 12 gave increased yields, 6 had no effect, and 3 gave diminished yields. The salts that gave increases encompassed diverse cations but were restricted to the anions Cl−, Br−, I−, and Ph4B− while SO42−, F−, or BF4− did not give improved yields. All 7 soluble tetraalkylammonium or tetraphenylphosphonium salts (F−, Cl−, Ph4B−, PF6−, or HSO4− counterions) that were surveyed gave yield increases of > 1.5 fold. Thus a 10−1 M pyrrole-benzaldehyde condensation catalyzed with 10−2 M BF3·O(Et)2 in CH2Cl2 containing 0.1 equiv of NaCl (5.85 mg/10 mL CH2Cl2) or 0.0031 equiv of benzyltributylammonium chloride (Bu3BzlNCl) (based on [benzaldehyde]) gave ∼50% yield compared with ∼25% in the reaction without salt. The pyrrole-aldehyde condensation is much faster in the presence of salt, as measured by the rate of disappearance of benzaldehyde and the rate of formation of the porphyrin. Yield increases in the presence of salt were observed with catalysis by BF3·O(Et)2, BF3·2H2O, and CF3CO2H. Significant salt effects also were observed with BF3·O(Et)2 or CF3CO2H in the solvent diethyl ether, but the maximum yield was 15%. A survey of nine aldehydes showed yield improvements of up to 2-fold in six cases in the presence of salt. During the pyrrole-aldehyde reaction in CH2Cl2 either in the presence or absence of soluble salts, the medium becomes heterogeneous (measured by nephelometry). The addition of water to BF3·O(Et)2 in CH2Cl2 also yields a heterogeneous medium; in the presence of salt this medium affords twice the yield of porphyrin as that formed in the absence of salt. 11B NMR and 19F NMR experiments failed to unveil any new species formed by interaction of chloride-containing salts with BF3·O(Et)2. The complexity of the reaction medium, as well as insufficient information about the nature of the pyrrole-aldehyde condensation, preclude an assignment of mechanisms underlying the salt effects. However, a rank ordering of salts in the porphyrin reaction does not correlate with their desiccative power, and the generality of the salt effects is at odds with the selective anion templating of tetrapyrrolic macrocycles. Irreversible features of the pyrrole-aldehyde condensation have been identified via exchange experiments during the course of the reaction and 13C NMR labeling experiments. The improved reaction conditions can be used for preparative-scale syntheses, as 720 mg tetraphenylporphyrin (47% yield) was obtained from a 100 mL-scale reaction with 0.1 M reactants at room temperature.}, number={37}, journal={TETRAHEDRON}, author={Li, FR and Yang, KX and Tyhonas, JS and MacCrum, KA and Lindsey, JS}, year={1997}, month={Sep}, pages={12339–12360} }
 @misc{li_gentemann_kalsbeck_seth_lindsey_holten_bocian_1997, title={Effects of central metal ion (Mg, Zn) and solvent on singlet excited-state energy flow in porphyrin-based nanostructures}, volume={7}, ISSN={["1364-5501"]}, DOI={10.1039/a700146k}, abstractNote={Zinc porphyrins have been widely used as surrogates for chlorophyll 
(which contains magnesium) in photosynthetic model systems and molecular 
photonic devices. In order to compare the photodynamic behaviour of Mg- 
and Zn-porphyrins, dimeric and star-shaped pentameric arrays comprised of 
free-base (Fb) and Mg- or Zn-porphyrins with intervening diarylethyne 
linkers have been prepared. A modular building block approach is used to 
couple ethynyl- or iodo-substituted porphyrins in defined metallation 
states (Fb, Mg or Zn)via a Pd-catalysed reaction in 2–6 h. 
The resulting arrays are purified in 45–80% overall yields by 
combinations of size exclusion chromatography and adsorption 
chromatography (≥95% purity). High solubility of the arrays in organic 
solvents facilitates chemical and spectroscopic characterization. The 
star-shaped Mg 
 4 
Fb- and Zn 
 4 
Fb-pentamers, where the 
Fb-porphyrin is at the core of the array, have pairwise interactions 
similar to those of dimeric MgFb- and ZnFb-arrays. The arrays have been 
investigated by static and time-resolved absorption and fluorescence 
spectroscopy, as well as resonance Raman spectroscopy. The major findings 
include the following. (1) The rate of singlet excited-state energy 
transfer from the Mg-porphyrin to the Fb-porphyrin [(31 
ps) 
 -1 
 ] is comparable to that from the Zn-porphyrin to 
the Fb-porphyrin [(26 ps) 
 -1 
 ] in the dimeric arrays. 
Qualitatively similar results are obtained for the star-shaped pentamers. 
The similar rates of energy transfer for the Mg- and Zn-containing arrays 
are attributed to the fact that the electronic coupling between the 
metalloporphyrin and Fb-porphyrin is approximately the same for Mg- 
vs. Zn-containing arrays. (2) The quantum yield of energy 
transfer is slightly higher in the Mg-arrays (99.7%) than in the Zn-arrays 
(99.0%) due to the longer inherent lifetime of Mg-porphyrins (10 ns) 
compared with Zn-porphyrins (2.5 ns). (3) The rate of energy transfer and 
the magnitude of the electronic coupling are essentially independent of 
the solvent polarity and the coordination geometry of the metalloporphyrin 
(four- or five-coordinate for Zn-porphyrins, five- or six-coordinate for 
Mg-porphyrins). (4) Polar solvents diminish the fluorescence yield and 
lifetime of the excited Fb-porphyrin in arrays containing either Mg- or 
Zn-porphyrins. These effects are attributed to charge-transfer quenching 
of the Fb-porphyrin by the adjacent metalloporphyrin rather than to 
changes in electronic coupling. The magnitude of the diminution is greater 
for the Mg-containing arrays, which is due to the greater driving force 
for charge separation. (5) The Zn-containing arrays are quite robust while 
the Mg-containing arrays are slightly labile toward demetallation and 
photooxidation. Taken together, these results indicate that 
porphyrin-based nanostructures having high energy-transfer efficiencies 
can be constructed from either Mg- or Zn-porphyrins. However, 
Mg-containing arrays may be superior in situations where a succession of 
energy-transfer steps occurs (due to a slightly higher yield per step) or 
where charge transfer is a desirable feature. On the other hand, 
Zn-porphyrins are better suited when it is desirable to avoid charge 
transfer quenching reactions. Accordingly, the merits of constructing a 
device from Mg- vs. Zn-containing porphyrins will be determined 
by the interplay of all of the above 
factors.}, number={7}, journal={JOURNAL OF MATERIALS CHEMISTRY}, author={Li, FR and Gentemann, S and Kalsbeck, WA and Seth, J and Lindsey, JS and Holten, D and Bocian, DF}, year={1997}, month={Jul}, pages={1245–1262} }