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Extending the applications of Photoremovable Protecting Groups (PPGs) to "cage" phenols has generally met with unusually complex PPG byproducts. In this study, we demonstrate that thep-hydroxyphenacyl (pHP) cage for both simple and complex phenolics, including tyrosine, dispenses free phenols. With the simpler unsubstituted phenols, the reaction is governed by their Bronsted Leaving Group ability. On the other hand, the byproducts of the cage vary with these phenols. For the more acidic phenols the cage byproduct follows the Favorskii rearrangement to formp-hydroxyphenylacetic acid whereas for the weaker phenols other reactions such as reduction and hydrolysis begin to emerge. When the photolysis is conducted in octa acid (OA) containers, non-Favorskii, unrearranged fragments of the cage and other byproducts arise. Kansas University Endowment Association National Institutes of HealthUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA National Science FoundationNational Science Foundation (NSF) [CHE-1807729] FCT - Foundation for Science and TechnologyPortuguese Foundation for Science and Technology [UID/Multi/04326/2019] operational program COMPETE 2020 [EMBRC.PT ALG-01-0145-FEDER-022121] info:eu-repo/semantics/publishedVersion

The two-photon absorption properties of anionic poly(phenylene ethynylene)-type conjugated oligo- and polyelectrolytes are studied in molecularly dissolved and aggregated forms in aqueous solution. Several different polyvalent cations are used to induce aggregation. It is found that both materials in the aggregated form exhibit enhanced two-photon excited fluorescence (2PEF) and two-photon cross section (σ2) compared with the molecularly dissolved structures. The 2PEF and σ2 are unaffected by the nature of the polyvalent cation that is used to induce aggregation. The two-photon absorption cross section enhancement arises because of the increase in the difference dipole moment (Δμ) in the aggregates of the conjugated materials, an effect that is attributed to the introduction of charge transfer character into the aggregate excited state.

The reactions of cis-[PtCl2{P(C6H4CH3-p)3}2] with HC C-C6H4R-p (R = NO2, CH3, OCH3), in the presence of CuCl catalyst, lead to the formation of mono-acetylide complexes trans-[PtCl{P(C6H4CH3-p)3}2(C C-C6H4R-p)] (R = NO2 1; R = CH3 2; R = OCH3, 3). These monochloro-acetylide complexes were further employed for the synthesis of symmetrical dinuclear platinum complexes. Thus, the reactions of HC C-C6H2(2,5-OC4H9)2-C CH with two molar equivalents of 1, 2 and 3, in the presence of CuCl catalyst, affords dinuclear complexes trans-trans-[Pt2{P(C6H4CH3-p)3}4(C C-C6H4R-p)2(C C-C6H2(OC4H9)2-C C)](R = NO2 4; R = CH3 5; R = OCH3; 6). All these mono- and dinuclear platinum complexes have been characterized by IR, 1H NMR, 31P NMR spectroscopy, and the molecular structures of 2 and 5 were unequivocally established by single crystal X-ray diffraction analyses. The thermal stability of these complexes has been studied by thermogravimetric analysis (TGA). The photophysical properties of these materials have been probed using electronic absorption and emission spectroscopy, and z-scan techniques.

We report the clean, efficient photorelease of a series of carboxylic acids embedded in octa acid (OA) host and protected by a p-hydroxyphenacyl cage. A key role is played by the cage by providing hydrophobicity for entry into the OA enclosure and yet readily removable as a photoactivated protecting group for release from the host. The rapid photo-Favorskii rearrangement of the departing chromophore does not react with the host OA but diminishes hydrophobicity of the OA contents, leading to their facile release into the solvent.

Two new cavitands substituted with acid and alcohol groups (tetra-acid tetra-alcohol [TATA] and inverted TATA [iTATA]) bearing the same molecular skeleton as octa acid (OA) have been synthesized and their use as photochemical reaction containers explored. Isothermal calorimetric titration experiments suggest that the inclusion of organic molecules within these cavitands is driven both by favorable ΔH and ΔS and the substituents at the portals have little role to play. Comparison of the 2 new cavitands with the previous results on OA reveals that the presence of benzoate anion at the top periphery is essential for the cavitand to be a triplet sensitizer. Polarity within the water-soluble capsules, resulting from TATA and iTATA, was found to be close to that of ethylacetate and hydrocarbons, similar to that of OA. Photophysical studies with anthracene and camphorthione as guests disclose that the capsules made of 2 molecules of cavitands do not disassemble in the time scale of the excited states of the above guests (S1 in the case of anthracene and T1 in the case of camphorthione). Capsules ability to confine guests and the resulting photochemical intermediates has been tested by examining the photochemistry of 1-phenyl-3-para-tolyl-2-propanone. The radicals resulting from the Norrish type 1 cleavage of 1-phenyl-3-para-tolyl-2-propanone did not escape the cage and gave products, resulting from 100% cage effect. Availability of TATA and iTATA along with already reported similar cavitands expands the list of water-soluble capsule forming cavitands that could be used as molecular containers.

Examples of release of organic acids from encapsulated p-methoxyphenacyl esters provided here demonstrate the value of a phototrigger strategy to release chemicals of interest in water from hydrophobic precursors. In this study, a photochemical beta-cleavage process centered on the p-methoxyphenacyl group is exploited to release the acid of interest from a water-soluble capsule made up of octa acid.

Two deep cavity cavitands, octa acid and resorcinol-capped octa acid, have been established to be good triplet energy donors in the excited state and electron donors in the ground state to excited acceptors. This property endows them the capacity to be “active” reaction containers. The above recognition provides opportunities to investigate the excited state chemistry of host-encapsulated guests without the use of secondary triplet energy and electron donors.