RESUMEN

We report herein the selective preparation of normal, tautomeric, and dual-fluorescent molecules with a common ESIPT core. 2'-Hydroxyacetophenone (OHAP) is known as a typical molecule that undergoes excited-state intramolecular hydrogen transfer (ESIPT) to display fluorescence emission from the excited state of the tautomer. In this study, a series of ten OHAP-cored fluorescent molecules were prepared and their excited state properties have been explored. The bathochromic shift of the π-π* absorption band with π-extensions of substituents of these molecules indicates that the excitation energy of the normal form of the OHAP unit was reduced due to the substituents, while the energy of the excited tautomer appeared to be independent of the π-extension of the substituents. When pyrene or anthracene was connected at the end (molecules 4 and 5), only normal fluorescence appeared, and the tautomer fluorescence disappeared. An anthracene derivative (molecule 10) displayed dual fluorescence, indicating that the normal and the tautomer excited states were energetically "balanced". A fluorescence lifetime analysis revealed the ESIPT reaction rate of 10 to be much slower than those of other derivatives and that the normal and tautomer forms were in equilibrium in the excited state.

RESUMEN

Upon photoirradiation of a stilbene-cored poly(glutamate) dendrimer, the photocrosslinking reaction preferentially occurred to produce the [2 + 2] cycloadduct in benzene. In addition, blue-shifted absorption spectra and a bisignate circular dichroism (CD) signal were observed, indicating that the aggregates of the stilbene core were chiral.

RESUMEN

The fluorescence quantum yield of cis-stilbene-cored rigid polyphenylene dendrimer (cis-G2) is 20% even at room temperature. Moreover, the fluorescence lifetime of cis-G2 is twice as long as that of the corresponding trans-isomer.

RESUMEN

A diphenylbutadiene-cored dendrimer exhibited a remarkably high quantum yield for trans-to-cis photoisomerization in aqueous solution. Analysis of the fluorescence lifetimes and the wavelength-dependent excitation spectra suggested that the core butadiene adopts multiple conformations, one or several of which is sufficiently distorted to undergo preferential photoisomerization.

RESUMEN

The compound 2-[(1E)-2-(1H-pyrrol-2-yl)ethenyl]-quinoxaline (PQX) is a promising fluorescent chromophore for the estimation of protein binding site polarity, due to its full-color solvatochromic fluorescence. A linear relationship was obtained between the peak emission wavenumber and E(T)(N) (normalized solvent polarity). The BSA binding site polarity was estimated from the solvatochromic plot.

Asunto(s)

RESUMEN

The series of linear-shaped phenylacetylenyl- and (phenylacetylenyl)phenylacetylenyl-substituted aromatic enediynes 1-3 were synthesized as pure trans and cis isomers and their photochemistry explored. With expansion of the π-electron system, the absorption spectra red-shifted and the molar extinction coefficients dramatically increased up to 122000 M(-1) cm(-1) for trans-3. The absorption spectra of cis-2 and cis-3 consisted of two independent absorption bands. The fluorescence quantum yields of the molecules were high, even for the cis isomers (Φ(f) = 0.39-0.61). The fluorescence decay of each of the compounds was analyzed as a single exponential and the wavelength dependence of time constants was not observed, indicating a single emitting state in all cases. All isomers exhibited mutual cis-trans photoisomerization. The quantum yield of both trans-to-cis and cis-to-trans photoisomerization considerably decreased in 2 and 3, presumably due to an increased number of photochemical processes that yield nonreactive excited species and which result in nonradiative deactivation. Three energy minima exist in the excited triplet state, where the energy of planar conformation decreased with the extension of the phenyl acetylenyl chain, resulting in the promotion of nonradiative processes without conformational change.

Asunto(s)