Signaling Recognition Events with Fluorescent Sensors and Switches.

6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

Design principles of fluorescent molecular sensors for cation recognition

Rhodamine dyes are widely used as fluorescent probes owing to their high absorption coefficient and broad fluorescence in the visible region of electromagnetic spectrum, high fluorescence quantum yield and photostability. A great interest in the development of new synthetic procedures for preparation of Rhodamine derivatives has arisen in recent years because for most applications the probe must be covalently linked to another (bio)molecule or surface. In this critical review the strategies for modification of Rhodamine dyes and a discussion on the variety of applications of these new derivatives as fluorescent probes are given (108 references).

Synthesis and applications of Rhodamine derivatives as fluorescent probes

Role of Structural Factors in the Nonlinear Optical Properties of Phthalocyanines and Related Compounds

Photoejection of cations from complexes with a crown-ether-linked merocyanine evidenced by ultrafast spectroscopy

Transient absorption in several symmetrical cyanine and carbncyanine dyes is measured by time-resolved spectroscopy with subpicosecond white-light continuum in a wide spectral range (0.35–1 μm). The results are compared with data available in the literature on ultrashort and long-lived transients. The linear shift law observed here for the S1Sn absorption bands in the wavelength scale allows one to predict the main induced absorption bands for members of several carbocyanine families (vinylogous series) which have not yet been studied. In the case of the shortest methine chains (cyanines and monocarbocyanines) a tew transient absorption bands are assigned to the formation of photoisomers. The absolute values of the excited-state or photoisomer cross sections of polymethine carbocyanines are evaluated by global spectral analysis, from the measured differential optical density spectra. Several cases of large values (higher than 10) of the absorption cross section ratio (excited/ground state) are found at new wavelengths, which allows applications of photo-induced absorption to photonics and laser technologies over a broad spectral range.

Transient absorption of symmetrical carbocyanines

The photoinduced processes in three dimethylamino derivatives of the triphenylphosphine oxide (OMAP, ODAP, and OTAP) are studied in solution at room temperature by time-resolved fluorescence spectroscopy with a streak camera and a 500 fs UV laser excitation source. These compounds exhibit a dual fluorescence in polar solvents explained by the fast formation of an emissive charge-transfer state as in the model compound (dimethylamino)benzonitrile (DMABN). Fluorescence decays are also measured for solutions of DMABN under the same conditions. For both compounds, the intramolecular charge-transfer time is shown to vary from a few picoseconds to a few tens of picoseconds depending on the polarity of the solvent and, for the triphenylphosphine derivatives, on the number of dimethylamino substituents. The charge-transfer process is described as a barrier-activated process with a solvent polarity dependent height. The solvent dynamics and solvent viscosity effects on the charge-transfer rate are examined for bot...

Role of Intramolecular Torsion and Solvent Dynamics in the Charge-Transfer Kinetics in Triphenylphosphine Oxide Derivatives and DMABN

Subpicosecond reverse saturable absorption in organic and organometallic solutions

Subpicosecond absorption spectroscopy and picosecond streak camera fluorometry are applied to the study of the photoinduced processes in three classes of compounds for which molecular torsion with charge localization leading to an emissive or non-emissive twisted internal charge transfer state was proposed. The compounds are classified according to their steady-state fluorescence properties: compounds having a single band without solvatochromism or a single band with solvatochromism and compounds exhibiting dual fluorescence in polar solvents. The selected compounds are di- and tri-phenylmethane and amino-rhodamine dyes for the first class, the laser dye DCM for the second class and a substituted triphenylphosphine for the third class. These compounds contain at least one electron-donating anilino-group able to rotate. In all cases, the transient spectroscopy gives evidence for an excited-state relaxation involving the formation of an intermediate state. The changes observed in the kinetics by changing the solvent viscosity and polarity and upon donor protonation bring support to a mechanism involving photoinduced charge transfer with structural change. The kinetics are tentatively discussed within the context of theories of electron transfer reactions in the condensed phase.

Y.H. Meyer

Papers

Photoejection of cations from complexes with a crown-ether-linked merocyanine evidenced by ultrafast spectroscopy

Transient absorption of symmetrical carbocyanines

Role of Intramolecular Torsion and Solvent Dynamics in the Charge-Transfer Kinetics in Triphenylphosphine Oxide Derivatives and DMABN

Subpicosecond reverse saturable absorption in organic and organometallic solutions

Investigation of excited-state charge transfer with structural change in compounds containing anilino subunits by subpicosecond spectroscopy