Uwe Leinhos

Bio: Uwe Leinhos is an academic researcher from University of Rochester. The author has contributed to research in topics: Excited state & Intramolecular force. The author has an hindex of 5, co-authored 6 publications receiving 576 citations. Previous affiliations of Uwe Leinhos include National Science Foundation.

Excited-state dipole moments of dual fluorescent 4-(dialkylamino)benzonitriles: influence of alkyl chain length and effective solvent polarity

Abstract: Singlet excited-state dipole moments of a number of aminobenzonitriles have been determined in cyclohexane, benzene, and 1,4-dioxane, using time-resolved microwave conductivity (TRMC) and fluorescence spectroscopy techniques. For the 4-(dialkylamino)benzonitriles (methyl, ethyl, propyl, and decyl) intramolecular charge transfer (ICT) occurs in the excited singlet state even in the nonpolar solvent cyclohexane

Intramolecular charge transfer in amino- benzonitriles: Requirements for dual fluorescence

Abstract: Dual fluorescence and intramolecular charge transfer (ICT) are observed with aminobenzonitriles when two excited state levels (Sl and S2(CT) in DMABN) have an energy gap sufficiently small for vibronic coupling: a solvent-induced pseudo-Jan-Teller effect. It is argued that the N-inversion of the amino group acts as a promoting mode. These conclusions are based on a comparison of absorption spectra and photostationary and time-resolved fluorescence data. Dual fluorescence is also observed with MMD, in which the dimethylamino group is twisted towards a perpendicular configuration with respect to the phenyl ring.

Novel intermolecular and intramolecular photochemical reactions initiated by excited state single electron transfer processes

Abstract: Several examples of photoinduced electron transfer initiated cation radical carboncarbon bond fragmentation reactions are reported. 1,2-aminoalcohols and 1,2-diamines undergo analogous fragmentation reactions although they show quite different reactivities. In general, the cation radicals of 1,2-diamines fragment more efficiently than those of aminoalcohols and the reactions are not dependent on the basicity of the reduced acceptor counterion species. A systematic study of 1,2-diamines indicates that the quantum efficiencies of the reaction are highly dependent on the reaction conditions (solvent, type of sensitizer, cosensitization, etc.) and structural considerations of the molecules being studied. Higher quantum efficiencies can be obtained using a triplet sensitizer or cosensitization. The effects of molecular orbital alignment on the efficiency of fragmentation were analyzed by modifying the structures of the 1,2-diamines. Interestingly, higher quantum yields are observed when certain molecular orbital configurations are achieved. Similar conclusions are obtained from studies of the reactivity of “remote” aminoalcohols and diamines. In this report, we also demonstrate that the quantum efficiency of the cation radical fragmentation can be improved dramatically by utilizing an efficient fragmentable electron acceptor as sensitizer (such as carbon tetrachloride). A new concept of “double fragmentation” is proposed.

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

Abstract: 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

Geometries and properties of excited states in the gas phase and in solution: theory and application of a time-dependent density functional theory polarizable continuum model.

Abstract: In this paper we present the theory and implementation of analytic derivatives of time-dependent density functional theory (TDDFT) excited states energies, both in vacuo and including solvent effects by means of the polarizable continuum model. The method is applied to two case studies: p-nitroaniline and 4-(dimethyl)aminobenzonitrile. For both molecules PCM-TDDFT is shown to be successful in supporting the analysis of experimental data with useful insights for a better understanding of photophysical and photochemical pathways in solution.

Fast Evaluation of Geometries and Properties of Excited Molecules in Solution: A Tamm-Dancoff Model with Application to 4-Dimethylaminobenzonitrile

Abstract: We present a method to evaluate ab initio energy, wave function, and gradient of a solvated molecule in an electronically excited state. In particular, this paper extends the Polarizable Continuum ...

On the development of sensor molecules that display Fe(III)-amplified fluorescence.

Abstract: Incorporation of a tailor-made size-restricted dithia-aza-oxa macrocycle, 1-oxa-4,10-dithia-7-aza-cyclododecane, via a phenyl linker into two fluorescent sensor molecules with electronically decoupled, rigidly fixed, and sterically preoriented architectures, a 1,3,5-triaryl-Delta2-pyrazoline and a meso-substituted boron-dipyrromethene (BDP), yields amplified fluorescence in the red-visible spectral range upon binding of Fe(III) ions. The response to Fe(III) and potentially interfering metal ions is studied in highly polar aprotic and protic solvents for both probes as well as in neat and buffered aqueous solution for one of the sensor molecules, the BDP derivative. In organic solvents, the fluorescence of both indicators is quenched by an intramolecular charge or electron transfer in the excited state and coordination of Fe(III) leads to a revival of their fluorescence without pronounced spectral shifts. Most remarkably, the unbound BDP derivative shows dual emission in water and can be employed for the selective ratiometric signaling of Fe(III) in buffered aqueous solutions.

Ultrafast Charge Transfer in Amino-Substituted Boron Dipyrromethene Dyes and Its Inhibition by Cation Complexation: A New Design Concept for Highly Sensitive Fluorescent Probes

Abstract: The photophysical behavior of a newly synthesized aza crown-substituted boron−dipyrromethene (BDP) dye and its dimethylamino analogue were investigated with steady-state and time-resolved fluorometry and compared to a reference compound. In solvents more polar than hexane, excitation of the dyes leads to a fast charge transfer from the locally excited (LE) state to a weakly emissive charge-transfer (CT) state. The donor-substituted compounds show dual emission from the LE and CT state, both fluorescence quantum yields being low. The rate constant of excited-state charge separation, calculated from the global analysis of time-resolved emission data, was determined to 1.6 × 1011 s-1 in 1,4-dioxane. The crowned compound forms 1:1-complexes with various alkali and alkaline-earth metal ions, which exist as two conformers in solution. In these complexes, coordination of the cation to the nitrogen donor atom of the crown inhibits the charge-transfer process, leading to a cation-dependent enhancement of the LE em...