Anthony David Debellis

An Extended Conical Intersection Seam Associated with a Manifold of Decay Paths: Excited-State Intramolecular Proton Transfer in O-Hydroxybenzaldehyde

O-Hydroxybenzaldehyde (OHBA) is a prototypical photoprotector exhibiting excited-state intramolecular proton transfer (ESIPT). Here we report how its photostability depends on an extended conical intersection seam associated with a manifold of decay paths. Thus, the photoreactivity of OHBA derives from a flat excited-state potential energy surface with barriers of only tenths of electronvolts between the reactant and several conical intersection structures that lead to different products: two isomers of a hydrogen-bonded intersection (HBI) that lead back to the enol reactant or to the tautomerized keto form in its Z conformation; an intersection (ZEI) that mediates the Z-E isomerization of the keto tautomer; and a twisted-pyramidalized one (TPI) that leads to an oxetene adduct. The intersection structures are connected to each other, forming a continuous seam, and the competition between the products depends on where the seam is accessed after the initial excitation. The overall picture must be also valid for the methyl salicylate and salicylic acid analogues of OHBA since it reflects the characteristics reported previously for MS and SA.

Unexpected Electronic Effects on Benzotriazole UV Absorber Photostability: Mechanistic Implications Beyond Excited State Intramolecular Proton Transfer

Electron withdrawing groups at the 5-position of benzotriazole ultraviolet absorbers (UVA) surprisingly improve photopermanence despite weakening the intramolecular hydrogen bond believed to be responsible for photostability. These results, encountered in coatings, thermplastics, and solvents, contradict the assumption from the widely accepted view of UVA photostability that a stronger H-bond would generate a more stable UVA. Calculations suggest the involvement of a conical intersection in benzotriazole excited state deactivation and support a significant role for charge transfer. Modifications to the traditional model of UVA photostability are discussed which more fully consider electronic factors and molecular motions other than H-transfer.

Facile Phosphite to Phosphonate Rearrangement of a Trialkanolamine-derived Triphosphite Promoted by Triethylaluminum 1

A facile room temperature rearrangement of a trialkanolamine-derived triphosphite, 1 , to the monophosphonate 5 promoted by three equivalents of triethylaluminum is described. The diphosphonate 6 was prepared by the addition of three equivalents of triethylaluminum to the monophosphonate 5 . A mechanism is suggested involving a transition state or intermediate with coordination of the trialkylaluminum to the migrating oxygen.

PRONOUNCED CONFORMATIONAL PREFERENCE OF THE 3?-?-CUMYL SUBSTITUENT IN 2-(2?-METHOXY-3?-?-CUMYLPHENYL)BENZOTRIAZOLE

A pronounced conformational preference of the 3′-α-cumyl substituent in 2-(2′-methoxy-3′-α-cumylphenyl)benzotriazole is suggested from the results of molecular dynamics simulations. This suggestion is supported by both solution NMR spectral and solid-state x-ray crystallographic data. The orientation of the α-cumyl substituent may have implications on the relative performance of 3′-substituted 2′-hydroxyphenylbenzotriazole light stabilizers in polar media.