Search

A broadly based investigation of the effects of a diverse array of substituents on the photochemical rearrangement of p-hydroxyphenacyl esters has demonstrated that common substituents such as F, MeO, CN, C[O.sub.2]R, CON[H.sub.2], and C[H.sub.3] have little effect on the rate and quantum efficiencies for the photo-Favorskii rearrangement and the release of the acid leaving group or on the lifetimes of the reactive triplet state. A decrease in the quantum yields across all substituents was observed for the release and rearrangement when the photolyses were carried out in buffered aqueous media at pHs that exceeded the ground-state p[K.sub.a] of the chromophore where the conjugate base is the predominant form. Otherwise, substituents have only a very modest effect on the photoreaction of these robust chromophores. Key words: substituent, pH, p[K.sub.a], solvent effects, photorelease. Une etude detailleee des effets de divers arrangements de substituants sur le rearrangement photochimique des esters de p-hydroxyphenacyle a demontre que les substituants communs, tel F, MeO, CN, C[O.sub.2]R ou C[H.sub.3], n'ont que peu d'effet sur la vitesse et les efficacitees quantiques du rearrangement de photo-Favorskii et sur la liberation du groupe acide partant ou sur les temps de vies de l'etat triplet reactif. On a observe que tous ces substituants provoquent des diminutions des rendements quantiques pour la liberation et le rearrangement quand les reactions de photolyse sont effectuees dans un milieu aqueux tamponnee a un pH superieur a celui du p[K.sub.a] de l'etat fondamental du chromophore pour lequel la base conjuguee est la forme predominante. Autrement, les substituants n'ont qu'un effet modeste sur la photoreaction de ces robustes chromophores. Mots-cles: substituant, pH, p[K.sub.a], effets de solvant, liberation photochimique. [Traduit par la Redaction], Introduction Among the known photoremovable protecting groups, p-hydroxyphenacyl (pHP, 1, eq. [1]) has consistently provided very fast (within a few nanoseconds after excitation or even less) and efficient, high conversion [...]

Spectral properties and fluorogenic behaviors of five novel thiophene variants of malachite green (MG), termed MGTs, were determined. Appreciable changes as a function of homologation and substitution pattern, including absorption band positions and intensities and fluorescence quantum yields were observed. In particular, the shorter wavelength y‐band absorption was found to shift over a nearly 200 nm range based on aryl group variation, allowing fine‐tuning of the excitation wavelength for these dyes. In addition, the fluorescence intensity of some MGTs increased significantly (up to 4600‐fold) when the dye was bound to a cognate protein partner, which is potentially useful for cell imaging studies. A series of malachite green (MG) analogues in which the phenyl group was replaced by various thiophenyl groups was synthesized and characterized. Substitution with increasing numbers of thiophenes led to a progressive redshift of the y‐band absorption allowing fine‐tuning of the excitation wavelength. Several of these dyes bound to a single‐chain antibody previously selected for binding to MG leading to 102–103‐fold fluorescence enhancements. [ABSTRACT FROM AUTHOR]