Photophysics and charge transfer in oligo(thiophene) based conjugated diblock oligomers.

This paper reports an investigation of the electronic structure and photophysical properties of two "diblock" π-conjugated oligomers (T4-TBT and T8-TBT) that feature electron rich tetra(thiophene) (T4) or octa(thiophene) (T8) segments linked to an electron poor 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT) moiety. Electrochemistry and UV-visible absorption spectroscopy reveals that the diblock oligomers display redox and absorption features that can be attributed to the Tn and TBT units. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations support the experimental electrochemistry and optical spectroscopy results, suggesting that the frontier orbitals on the diblock oligomers retain characteristics of the individual π-conjugated segments. However, low energy optical transitions are anticipated to arise from Tn to TBT charge transfer. Fluorescence spectroscopy on the diblock oligomers reveals that the oligomers feature strongly solvent dependent fluorescence. In non-polar solvents (hexane, toluene), the emission is structured with a moderate Stokes shift; however, in more polar solvents the emission becomes broader, and red-shifts significantly. Transient absorption spectroscopy on timescales from femtoseconds (fs) to microseconds (µs) reveals that in non-polar solvents excitation produces a singlet excited state (LE) that decays uniformly to the ground state in parallel with intersystem crossing to a triplet state. By contrast, in more polar solvents, excitation produces a very short-lived excited state (1-3 ps) which evolves rapidly into a second excited state that is attributed to the charge transfer (CT) state. The fast dynamics are associated with crossing from the LE state, which is populated initially by photoexcitation, into the CT state, which then decays to the ground state. The photophysical properties and dynamics of the LE and CT excited states are very similar for T4-TBT and T8-TBT, suggesting that the length of the oligo(thiophene) segment does not have a strong influence on the energy, structure or dynamics of the LE and CT excited states.

Competing pathways for photoremovable protecting groups: the effects of solvent, oxygen and encapsulation.

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 the p-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 Brønsted 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 form p-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.

Excited-State Intramolecular Proton-Transfer Properties of Three Tris(N-Salicylideneaniline)-Based Chromophores with Extended Conjugation.

The synthesis and photophysical properties of three tris(N-salicylideneaniline) (TSA) compounds containing 1,3,5-triarylbenzene, -tristyrylbenzene, and -tris(arylethynyl)benzene core units are reported. The TSA compounds underwent efficient excited-state intramolecular proton transfer (ESIPT) in solution and in solid state due to the preformed C=N⋅⋅⋅H-O hydrogen-bonded motifs of the structures. Steady-state fluorescence emission spectra of the TSA molecules revealed dual bands only in DMSO, and large Stokes shifts in other polar aprotic and protic solvents. Femtosecond transient absorption spectroscopic measurements in THF revealed lifetime values in the range of 14-16 ps for the excited-state keto-tautomer. The TSA compounds are also responsive to metal ions (Cu2+ and Zn2+ ) in DMSO, exhibit enhanced aggregate-induced emission (AIE) properties in DMSO/water mixtures, and are highly luminescent in the solid state.

Synthesis, characterization, guest inclusion, and photophysical studies of gold nanoparticles stabilized with carboxylic acid groups of organic cavitands.

Water-soluble gold nanoparticles (AuNP) stabilized with cavitands having carboxylic acid groups have been synthesized and characterized by a variety of techniques. Apparently, the COOH groups similar to thiol are able to prevent aggregation of AuNP. These AuNP were stable either as solids or in aqueous solution. Most importantly, these cavitand functionalized AuNP were able to include organic guest molecules in their cavities in aqueous solution. Just like free cavitands (e.g., octa acid), cavitand functionalized AuNP includes guests such as 4,4'-dimethylbenzil and coumarin-1 through capsule formation. The exact structure of the capsular assembly is not known at this stage. Upon excitation there is communication between the excited guest present in the capsule and gold atoms and this results in quenching of phosphorescence from 4,4'-dimethylbenzil and fluorescence from coumarin-1.

Gold nanoparticles functionalized with deep-cavity cavitands: synthesis, characterization, and photophysical studies.

In this report, we present methods of functionalization of AuNP's with deep-cavity cavitands that can include organic molecules. Two types of deep-cavity cavitand-functionalized AuNP's have been synthesized and characterized, one soluble in organic solvents and the other in water. Functionalized AuNP soluble in organic solvents forms a 1:1 host-guest complex where the guest is exposed to the exterior solvents. The one soluble in water forms a 2:1 host-guest complex where the guest is protected from solvent water. Phosphorescence from thiones and benzil included within heterocapsules attached to AuNP was quenched by gold atoms present closer to the guests included within deep-cavity cavitands. During this investigation, we have synthesized four new deep-cavity cavitands. Of these, two thiol-functionalized hosts allowed us to make stable AuNP's. However, AuNP's protected with two amine-functionalized cavitands tended to aggregate within a day.

Rapid and Effective Inactivation of SARS-CoV-2 with a Cationic Conjugated Oligomer with Visible Light: Studies of Antiviral Activity in Solutions and on Supports.

This paper presents results of a study of a new cationic oligomer that contains end groups and a chromophore affording inactivation of SARS-CoV-2 by visible light irradiation in solution or as a solid coating on paper wipes and glass fiber filtration substrates. A key finding of this study is that the cationic oligomer with a central thiophene ring and imidazolium charged groups gives outstanding performance in both the killing of E. coli bacterial cells and inactivation of the virus at very short times. Our introduction of cationic N-methyl imidazolium groups enhances the light activation process for both E. coli and SARS-CoV-2 but dampens the killing of the bacteria and eliminates the inactivation of the virus in the dark. For the studies with this oligomer in solution at a concentration of 1 µg/mL and E. coli, we obtain 3 log killing of the bacteria with 10 min of irradiation with LuzChem cool white lights (mimicking indoor illumination). With the oligomer in solution at a concentration of 10 µg/mL, we observe 4 log inactivation (99.99%) in 5 min of irradiation and total inactivation after 10 min. The oligomer is quite active against E. coli on oligomer-coated paper wipes and glass fiber filter supports. The SARS-CoV-2 is also inactivated by oligomer-coated glass fiber filter papers. This study indicates that these oligomer-coated materials may be very useful as wipes and filtration materials.

Aggregation-Enhanced Two-Photon Absorption of Anionic Conjugated Polyelectrolytes.

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.

Highly Effective Inactivation of SARS-CoV-2 by Conjugated Polymers and Oligomers.

In the present study, we examined the inactivation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by synthetic conjugated polymers and oligomers developed in our laboratories as antimicrobials for bacteria, fungi, and nonenveloped viruses. The results show highly effective light-induced inactivation with several of these oligomers and polymers including irradiation with near-UV and visible light. In the best case, one oligomer induced a 5-log reduction in pfu/mL within 10 min. In general, the oligomers are more active than the polymers; however, the polymers are active with longer wavelength visible irradiation. Although not studied quantitatively, the results show that in the presence of the agents at concentrations similar to those used in the light studies, there is essentially no dark inactivation of the virus. Because three of the five materials/compounds examined are quaternary ammonium derivatives, this study indicates that conventional quaternary ammonium antimicrobials may not be active against SARS-CoV-2. Our results suggest several applications involving the incorporation of these materials in wipes, sprays, masks, and clothing and other personal protection equipment that can be useful in preventing infections and the spreading of this deadly virus and future outbreaks from similar viruses.

Highly Effective Inactivation of SARS-CoV-2 by Conjugated Polymers and Oligomers.

The current Covid-19 Pandemic caused by the highly contagious SARS-CoV-2 virus has proven extremely difficult to prevent or control. Currently there are few treatment options and very few long-lasting disinfectants available to prevent the spread. While masks and protective clothing and social distancing may offer some protection, their use has not always halted or slowed the spread. Several vaccines are currently undergoing testing; however there is still a critical need to provide new methods for inactivating the virus before it can spread and infect humans. In the present study we examined the inactivation of SARS-CoV-2 by synthetic conjugated polymers and oligomers developed in our laboratories as antimicrobials for bacteria, fungi and non-enveloped viruses. Our results show that we can obtain highly effective light induced inactivation with several of these oligomers and polymers including irradiation with near-UV and visible light. With both the oligomers and polymers, we can reach several logs of inactivation with relatively short irradiation times. Our results suggest several applications involving the incorporation of these materials in wipes, sprays, masks and clothing and other Personal Protection Equipment (PPE) that can be useful in preventing infections and the spreading of this deadly virus and future outbreaks from similar viruses.

Photorelease of incarcerated guests in aqueous solution with phenacyl esters as the trigger.

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.

Release of guests from encapsulated masked hydrophobic precursors by a phototrigger.

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 ß-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.

Photochemical reaction containers as energy and electron-transfer agents.

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.