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

The Stability of Cyclodextrin Complexes in Solution.

Dielectric Relaxation and Solvation Dynamics of Water in Complex Chemical and Biological Systems

Although water is often hailed as the lubricant of life, a detailed understanding of its role in many chemical and biological processes still eludes us. In many natural systems, water is confined in an environment where its free movement is restricted and its three-dimensional hydrogen-bonded network is disrupted. Very recently, several groups applied ultrafast laser spectroscopy to study the dynamics of the constrained water molecules. It is observed that the dynamic behavior of the confined water molecules is markedly different from that of the ordinary water molecules. The most striking result is the bimodal response of confined water, with one bulk water-like subpicosecond component and a much slower component in a time scale of hundreds or thousands of picoseconds. This slow second component constitutes 10−30% of the total response and is crucial in the understanding of the role of water in complex chemical and biological processes. The origin of the slow component has been a subject of intense recen...

Slow dynamics of constrained water in complex geometries

Effect of cyclodextrine cavity size on twisted intramolecular charge transfer emission: Dimethylamino benzonitrile in β-cyclodextrine

Twisted intramolecular charge transfer emission of dimethylaminobenzonitrile in α-cyclodextrine cavities

Role of twisted intramolecular charge transfer in the fluorescence sensitivity of biological probes: Diethylaminocoumarin laser dyes

Steady-state and time-resolved studies on the emission properties of three 7-(diethylamino)coumarin laser dyes (I-III) in aqueous {gamma}-cyclodextrin ({gamma}-CD) solutions are reported. On addition of {gamma}-CD, fluorescence maxima of all the three dyes shift to higher energy, with a huge enhancement of the yield of intramolecular charge transfer (ICT) emission for the flexible ones (I and II) and a very slight enhancement for the rigid analogue III. The results are explained in terms of the concept of polarity-dependent twisted ICT rates. It is proposed that twisted ICT, the main nonradiative process in the excited ICT states of these dyes, is severely restricted inside the {gamma}-cyclodextrin cavity because of the reduced polarity. This is responsible for the enhancement of fluorescence from the ICT state.

Effect of .gamma.-cyclodextrin on the intramolecular charge transfer processes in aminocoumarin laser dyes

Steady-state absorption and emission spectra of p-N,N-dimethylaminobenzonitrile (DMABN) have been studied in aqueous γ-cyclodextrin (γ-CD) solutions. Two kinds of DMABN: γ-CD complexes with distinctly different excitation spectra are observed. For complexes in which the DMABN molecule is totally enclosed inside the γ-CD cavity, the twisted intramolecular charge transfer (TICT) is severely suppressed with a corresponding large enhancement of the ‘non-polar’ emission, while for partially enclosed DMABN molecules the TICT emission is only slightly enhanced. The fact that the TICT is inhibited inside the very large γ-CD cavity conclusively proves that the TICT phenomenon is polarity controlled.

Ashis Nag

Papers

Effect of cyclodextrine cavity size on twisted intramolecular charge transfer emission: Dimethylamino benzonitrile in β-cyclodextrine

Twisted intramolecular charge transfer emission of dimethylaminobenzonitrile in α-cyclodextrine cavities

Role of twisted intramolecular charge transfer in the fluorescence sensitivity of biological probes: Diethylaminocoumarin laser dyes

Effect of .gamma.-cyclodextrin on the intramolecular charge transfer processes in aminocoumarin laser dyes

Dual luminescence of dimethylaminobenzonitrile in γ-cyclodextrin. Environmental effects on twisted intramolecular charge-transfer phenomenon