Triplet-triplet annihilation photon-upconversion in hydrophilic media with biorelevant cholesteryl triplet energy acceptors

Funding Information: The Academy of Finland (Grant No. 316893) Funding Information: YJY is thankful for the support from the Kilpatrick Graduate Fellowship and the Starr Fieldhouse Research Fellowship Programs at Illinois Tech. The authors thank the National Science Foundation for the generous support to this work under a CAREER grant N° 1753012 Awarded to AJA. JI, ND and TL also thank the Academy of Finland for the generous support to this work under grant N° 316893. Publisher Copyright: © 2021 Elsevier B.V.We report two new biorelevant cholesteryl-based triplet energy acceptors, derivatives of DPA or 9,10-diphenylanthracene (C–DPA and C2–DPA). Using two different triplet sensitizers: QDN (ET ≈ 1.67 eV in PEG200) and PdTPP (ET ≈ 1.78 eV in PEG200), we were able to achieve both endothermic (with QDN) and exothermic (with PdTPP) triplet sensitization of DPA, C–DPA and C2–DPA in hydrophilic PEG200 media. While the maximum rate of triplet energy transfer (TET) was achieved with PdTPP and DPA (kTET = 4.7 × 107 M−1 s−1), for the cholesteryl-based acceptors, we found that the kinetic of the TET process was dependent upon the concentration of the acceptor. For PdTPP/C–DPA pair, the rate of the dynamic triplet energy quenching was kTET = 1.9 × 107 M−1 s−1; however, at higher concentrations of the quencher, the system reached a stationary state due to formation of self-assembled sub-domains of C–DPA that likely slowed the TET process. It was also found that this aggregation of C–DPA in PEG200 led to a 3.5 folds increase in the Ith compared to 133 mW cm2 for DPA. Subsequently, we estimated the ΦUC for these donor/acceptor pairs: QDN/DPA, PdTPP/DPA, and PdTPP/C–DPA. With respect to the estimated threshold intensity (Ith), we found that the quantum yields of TTA-UC were 2 ≤ QYUC≤12%.Peer reviewe

Stereospecific Photochemical Transformations Involving Axially Chiral Acrylanilides and a-Oxoamides

Asymmetric photochemical transformations have been under-explored due to the ineffectiveness of conventional methodologies/reagents/catalysts (point chiral auxiliaries and inductors) that were generally employed for thermal reactions. This limitation to use point chiral auxiliaries for asymmetric photochemistry is partly due to the asynchronous behavior of photo-excitation and chiral transfer/induction processes. This dissertation describes a complementary approach to conventional methodologies involving light induced chirality transfer from atropisomeric viz axially chiral molecular reactants (acrylanilides and α-oxoamides) to enantiopure product(s) with point chirality. The study has revealed the importance of rotamers control in the ground state and how it can impact the stereospecificity during light induced excited state reactions leading to enantiopure product(s). Con-rotatory 6π-photocyclization of axially chiral acrylanilides was explored under various reaction conditions. For example, α,β-unsaturated acrylanilides gave the expected 3,4-dihydroquinolin-2- one photoproduct(s) with enantiomeric excess (ee) values > 90% in both direct and triplet sensitized irradiations. On the other hand, the solution phase direct irradiations of α-substituted acrylanilides yielded racemic photoproduct(s) whereas the triplet sensitized reactions led to ee values > 90% in the expected photoproduct(s). By changing the reaction medium from isotropic media to solid state, α-substituted acrylanilides gave photoproducts with ee values as high as 70%. In addition to the effect of the reaction medium and the reactive spin state on the enantioselectivity, preliminary evaluation of the role of Lewis acid(s) and heavy cations (Na+, K+ and Cs+) were explored. The initial observations were quite promising with ee values up to 90% in the photoproducts upon direct irradiation in isotropic media. The photochemical γ-hydrogen abstraction reaction involving axially chiral α-oxoamides leading to β-Lactam photoproducts was investigated. The enantiomeric ratio (e.r.) > 90:10 in the expected β- Lactam photoproducts was found to be dependent on the temperature under which the irradiation was performed. Furthermore, elevated pressure was employed to counter the effect of elevated temperature and slow the rotation around N-C(aryl) chiral axis leading enantioenriched β-Lactam photoproducts. This dissertation details the overall mechanistic rationales and photophysical control studies during the photochemical transformations of atropisomeric acrylanilides and α-oxoamides leading to chirally enriched products

Light-Induced Transfer of Molecular Chirality in Solution: Enantiospecific Photocyclization of Molecularly Chiral Acrylanilides

Light-Induced Transfer of Molecular Chirality in Solution: Enantiospecific Photocyclization of Molecularly Chiral Acrylanilide