Steady-state and femtosecond transient absorption spectroscopy of new two-photon absorbing fluorene-containing quinolizinium cation membrane probes.

The synthesis, linear photophysical characterization, and nonlinear optical properties of two new symmetrical fluorene-containing quinolizinium derivatives, 2,8-bis((E)-2-(7-(diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl)vinyl)quinolizinium hexafluorophosphate (1) and 2,8-bis((E)-2-(7-((7-(diphenylamino)-9,9-dihexyl-9H-fluoren-2-yl)ethynyl)-9,9-dihexyl-9H-fluoren-2yl)vinyl)quinolizinium hexafluorophosphate (2), are reported. The nature of the dual-band steady-state fluorescence emission of 1 and 2 was determined, and violation of Kasha's rule along with a strong dependence on solvent polarity were shown. A relatively complex structure of two-photon absorption (2PA) spectra of 1 and 2, with maximum cross sections of ∼400-600 GM, was determined using the open aperture Z-scan method.

Superfluorescent squaraine with efficient two-photon absorption and high photostability.

The synthesis, linear photophysical, two-photon absorption (2PA), femtosecond transient absorption, and superfluorescence properties of a new symmetrical squaraine derivative (1) are reported. Steady-state linear spectral and photochemical properties, fluorescence lifetimes, and excitation anisotropy of 1 were investigated in various organic solvents. High fluorescence quantum yields (≈0.

Efficient photochromic transformation of a new fluorenyl diarylethene: one- and two-photon absorption spectroscopy.

Efficient reversible phototransformation of a new diarylethene-fluorene derivative, 1,2-bis(5-(9,9-didecyl-7-nitro-9H-fluoren-2-yl)-2-methylthiophen-3-yl)cyclopent-1-ene (1), was demonstrated in organic media under low-intensity laser excitation. Linear photophysical characterization of 1 was performed at room temperature in solvents of different polarity and viscosity. Significantly, close to unity quantum yield for the cyclization reaction of 1 was shown in nonpolar solutions.

Fluorene-based metal-ion sensing probe with high sensitivity to Zn2+ and efficient two-photon absorption.

The photophysical, photochemical, two-photon absorption (2PA) and metal ion sensing properties of a new fluorene derivative (E)-1-(7-(4-(benzo[d]thiazol-2-yl)styryl)-9,9-bis(2-(2-ethoxyethoxy)ethyl)-9H-fluoren-2-yl)-3-(2-(9,10,16,17,18,19,21,22,23,24-decahydro-6H dibenzo[h,s][1,4,7,11,14,17]trioxatriazacycloicosin-20(7H)-yl)ethyl)thiourea (1) were investigated in organic and aqueous media. High sensitivity and selectivity of 1 to Zn(2+) in tetrahydrofuran and a water/acetonitrile mixture were shown by both absorption and fluorescence titration. The observed complexation processes corresponded to 1:1 stoichiometry with the range of binding constants approximately (2-3) x 10(5) M(-1).

Are density functional theory predictions of the Raman spectra accurate enough to distinguish conformational transitions during amyloid formation?

We report density functional theory (DFT) calculations of the Raman spectra for hexapeptides of glutamic acid and lysine in three different conformations (alpha, beta and PPII). The wave numbers of amide I, amide II and amide III bands of all three conformations predicted at B3LYP/6-31G and B3LYP/6-31G* are in good agreement with previously reported experimental values of polyglutamic acid and polylysine. Agreement with experiment improves when polarization functions are included in the basis set.

DFT-based methods in the design of two-photon operated molecular switches.

Conjugated organic molecules with photochromic properties are being extensively studied as prospective optical switching and data storage materials. Among different photochromic compounds, diarylethenes demonstrate thermal stability, fatigue resistance, and high quantum yield. The mechanism of photoswitching in diarylethenes involves a symmetry-allowed conrotatory electrocyclic reaction, initiated by UV light.