Nikolaus P. Ernsting

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Organization: Institut für Chemie Humboldt-Universit?t zu Berlin Brook-Taylor-Strasse 2 , Germany

Department: Institut für Chemie Humboldt-Universität zu Berlin Brook-Taylor-Strasse 2

Title: (PhD)

TOPICS

Physical Chemistry

Chemicals
References

Effect of a Tertiary Butyl Group on Polar Solvation Dynamics in Aqueous Solution: Femtosecond Fluorescence Spectroscopy

Co-reporter:Mario Gerecke, Celin Richter, Martin Quick, Ilya N. Ioffe, Rainer Mahrwald, Sergey A. Kovalenko, and Nikolaus P. Ernsting

The Journal of Physical Chemistry B October 19, 2017 Volume 121(Issue 41) pp:9631-9631

Publication Date(Web):September 25, 2017

DOI:10.1021/acs.jpcb.7b05031

We monitor the time-dependent Stokes shift (TDSS) of fluorescence from the zwitterionic probe N-methyl-6-oxyquinolinium betaine in water. A spectral relaxation time τsolv = 0.57 ps (at 20.5 °C) is attributed to a solvation process involving water in the hydration layer. In this article we show that a tertiary butyl group, when attached to the chromophore, slows the dynamics to τsolv = 0.76 ps and increases the corresponding activation energy by 5 kJ/mol. In a companion paper (10.1021/acs.jpcb.7b05039), simulations suggest that the observed slow-down indicates coupling of solute vibrations to hydration water. Thus, a new angle on a thoroughly researched topic, solvation dynamics, has been opened.

Isosteric and fluorescent DNA base pair formed by 4-amino-phthalimide and 2,4-diaminopyrimidine: melting, structure, and THz polar solvation dynamics

Co-reporter:L. Dehmel, F. Berndt, M. Weinberger, M. Sajadi, I. Ioffe, H.-A. Wagenknecht and N. P. Ernsting

Physical Chemistry Chemical Physics 2016 vol. 18(Issue 9) pp:6813-6820

Publication Date(Web):09 Feb 2016

DOI:10.1039/C5CP06972F

An artificial base pair in the center of a duplex DNA oligomer, formed by 2,4-diaminopyrimidine and fluorescent 4-aminophthalimide C-nucleosides, is characterized spectroscopically, with a view towards its use in femtosecond solvation dynamics. Quantum-chemical calculations predict H-bonding energy equivalent to A:T. UV-vis absorption spectra provide insight into local melting at the 4-aminophthalimide modification site. Increase of temperature to nearly the melting temperature of the duplex leads to better hybridisation of the fluorescent nucleoside, contrary to native base pairs. This unusual observation is explained by the NMR solution structure of the duplex. Two conformations are adopted by the artificial pair due to backbone constraints, having either two or one interbase hydrogen bonds. In the latter, hydrogen bonding sites remain accessible for water solvation. The time-resolved dynamic Stokes' shift of 4-aminophthalimide fluorescence is consistent with that of a mixture of a slow and fast species. From the observations, the optimal linkage between 4-aminophthalimide and 2-deoxyribose for fitting into the duplex B-DNA structure is deduced.

Perpendicular State of an Electronically Excited Stilbene: Observation by Femtosecond-Stimulated Raman Spectroscopy

Co-reporter:Martin Quick, Alexander L. Dobryakov, Ilya N. Ioffe, Alex A. Granovsky, Sergey A. Kovalenko, and Nikolaus P. Ernsting

The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 20) pp:4047-4052

Publication Date(Web):September 29, 2016

DOI:10.1021/acs.jpclett.6b01923

In the photoisomerization path of stilbene, a perpendicular state P on the S1 potential energy surface is expected just before internal conversion through a conical intersection S1/S0. For decades the observation of P was thwarted by a short lifetime τP in combination with slow population flow over a barrier. But these limitations can be overcome by ethylenic substitution. Following optical excitation of trans-1,1′-dicyanostilbene, P is populated significantly (τP = 27 ps in n-hexane) and monitored by an exited-state absorption band at 370 nm. Here we report stimulated Raman lines of P. The strongest, at 1558 cm–1, is attributed to stretching vibrations of the phenyl rings. Transient electronic states, resonance conditions, and corresponding Raman signals are discussed.

Dual-fluorescence pH probe for bio-labelling

Co-reporter:C. Richter, C. Schneider, M. T. Quick, P. Volz, R. Mahrwald, J. Hughes, B. Dick, U. Alexiev and N. P. Ernsting

Physical Chemistry Chemical Physics 2015 vol. 17(Issue 45) pp:30590-30597

Publication Date(Web):19 Oct 2015

DOI:10.1039/C5CP05454K

Although seminaphtorhodafluor (SNARF) dyes are already widely used to measure pH in cells and at biofilms, their synthesis has low yield and results in an unspecific position of a carboxy-group. The separation of 5′- and 6′-carboxy-SNARF reveals a pKa difference of 0.15, calling into question pH measurements with the (commercially available) mixture. Here we replace the bulky external dicarboxyphenyl ring with a propionate group and evaluate the spectral properties of the new derivative. Proceeding to the ethyl-iodoacetamide, covalent linkage to cysteine protein sites is achieved efficiently as shown with a cyanobacterial phytochrome, extending the scarce application of SNARF in bio-labelling in the current literature. Application in fluorescence lifetime imaging is demonstrated both with the lifetime-based and ratiometric-yield method.

Resonance Femtosecond-Stimulated Raman Spectroscopy without Actinic Excitation Showing Low-Frequency Vibrational Activity in the S2 State of All-Trans β-Carotene

Co-reporter:Martin Quick; Alexander L. Dobryakov; Sergey A. Kovalenko

The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 7) pp:1216-1220

Publication Date(Web):March 17, 2015

DOI:10.1021/acs.jpclett.5b00243

Raman scattering with stimulating femtosecond probe pulses (FSR) was used to observe vibrational activity of all-trans β-carotene in n-hexane. The short-lived excited electronic state S2 was accessed in two ways: (i) by transient FSR after an actinic pulse to populate the S2 state, exploiting resonance from an Sx ← S2 transition, and (ii) by FSR without actinic excitation, using S2 ↔ S0 resonance exclusively and narrow-band Raman/broad-band femtosecond probe pulses only. The two approaches have nonlinear optical susceptibilities χ(5) and χ(3), respectively. Both methods show low-frequency bands of the S2 state at 200, 400, and ∼600 cm–1, which are reported for the first time. With (ii) the intensities of low-frequency vibrational resonances in S2 are larger compared to those in S0, implying strong anharmonicities/mode mixing in the excited state. In principle, for short-lived electronic states, the χ(3) method should allow the best characterization of low-frequency modes.

Observing the Hydration Layer of Trehalose with a Linked Molecular Terahertz Probe

Co-reporter:Mohsen Sajadi, Falko Berndt, Celin Richter, Mario Gerecke, Rainer Mahrwald, and Nikolaus P. Ernsting

The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 11) pp:1845-1849

Publication Date(Web):May 9, 2014

DOI:10.1021/jz500437c

The terahertz (THz) absorption bands of biomolecular hydration layers are generally swamped by absorption from bulk water. Using the disaccharide trehalose, we show that this limitation can be overcome by attaching a molecular probe. By time-resolving the fluorescence shift of the probe, a local THz spectrum is obtained. From the dependence on temperature and H2O/D2O exchange, it is concluded that the trehalose hydration layer is being observed. The region of dynamic water perturbation by the disaccharide encompasses the probe and is therefore larger than the first two solvation layers.Keywords: solvation; time-dependent Stokes shift; water dielectric dispersion;

Time-resolved laser spectroscopy of nonreactive processes in ionic liquids and their binary mixtures with organic solvents and CO2

Co-reporter:N.P. Ernsting, T. Lenzer, K. Oum

Journal of Molecular Liquids 2014 192() pp: 87-93

Publication Date(Web):

DOI:10.1016/j.molliq.2013.08.010

Synthesis of 4-Aminophthalimide and 2,4-Diaminopyrimidine C-Nucleosides as Isosteric Fluorescent DNA Base Substitutes

Co-reporter:Michael Weinberger, Falko Berndt, Rainer Mahrwald, Nikolaus P. Ernsting, and Hans-Achim Wagenknecht

The Journal of Organic Chemistry 2013 Volume 78(Issue 6) pp:2589-2599

Publication Date(Web):February 5, 2013

DOI:10.1021/jo302768f

The 4-aminophthalimide C-nucleoside 1 was designed as an isosteric DNA base surrogate, and a synthetic route to nucleoside 1 together with the 2,4-diaminopyrimidine-C-nucleoside 2 as a potential counterbase was worked out. The key steps in both synthetic routes represent a stereoselective Heck-type palladium-catalyzed cross-coupling with 2′-deoxyribofuranoside glycal followed by stereoselective reduction with NaBH(OAc)3. The nucleoside 1 shows a solvatofluorochromic behavior and significantly red-shifted fluorescence in solvents of high polarity and with hydrogen bonding capabilities. Both nucleosides 1 and 2 can be further processed to the corresponding phosphoramidite as DNA building blocks that allow incorporation of these chromophores as artificial DNA bases by automated DNA synthesis. The combination of the poor stacking properties of 1 and the hydrogen bonding interface at the phthalimide functionality that does not fit to any of natural DNA bases in the counterstrand yields destabilization of the duplex by 4–11 °C. The fluorescence of 1 in a representative double stranded DNA is characterized by a large Stokes’ shift and a quantum yield of approximately 12%. These are remarkable optical properties considering the very small size of the chromophore and indicate a high potential of these nucleoside analogues for fluorescent DNA analytics and imaging.

Fluorescence following Excited-State Protonation of Riboflavin at N(5)

Co-reporter:Martin Quick, Alexander Weigel, and Nikolaus P. Ernsting

The Journal of Physical Chemistry B 2013 Volume 117(Issue 18) pp:5441-5447

Publication Date(Web):April 10, 2013

DOI:10.1021/jp312571d

Excited-state protonation of riboflavin in the oxidized form is studied in water. In the −1 < pH < 2 range, neutral and N(1)-protonated riboflavin coexist in the electronic ground state. Transient absorption shows that the protonated form converts to the ground state in <40 fs after optical excitation. Broadband fluorescence upconversion is therefore used to monitor solvation and protonation of the neutral species in the excited singlet state exclusively. A weak fluorescence band around 660 nm is assigned to the product of protonation at N(5). Its radiative rate and quantum yield relative to neutral riboflavin are estimated. Protonation rates agree with proton diffusion times for H+ concentrations below 5 M but increase at higher acidities, where the average proton distance is below the diameter of the riboflavin molecule.

Excess Dynamic Stokes Shift of Molecular Probes in Solution

Co-reporter:Mohsen Sajadi and Nikolaus P. Ernsting

The Journal of Physical Chemistry B 2013 Volume 117(Issue 25) pp:7675-7684

Publication Date(Web):May 30, 2013

DOI:10.1021/jp400473n

The solvation dynamics of molecular probes is studied by broad-band fluorescence upconversion. The time-dependent position of the S1 → S0 emission band or of a vibronic line shape is measured with ∼80 fs, 10 cm–1 resolution. Polar solutes in acetonitrile and acetone, when excited into S1 with excess vibrational energy, show a dynamic Stokes shift which extends to the red beyond the quasistationary state. Equilibrium is then reached by a slower blue shift on a 10 ps time scale. In methanol, excess vibrational energy as large as ∼14 000 cm–1 shows no such effect. Nonpolar solutes exhibit an excess red shift of the emission band in both polar and nonpolar solvents even upon excitation near the vibronic origin. The observed dynamics are discussed in terms of transient heating of the excited chromophore, conformational change, and changes of the molecular cavity size. For solvation studies the optical excitation should be chosen close to the band origin.

Barrierless photoisomerisation of the “simplest cyanine”: Joining computational and femtosecond optical spectroscopies to trace the full reaction path

Co-reporter:Alexander Weigel, Matthias Pfaffe, Mohsen Sajadi, Rainer Mahrwald, Roberto Improta, Vincenzo Barone, Dario Polli, Giulio Cerullo, Nikolaus P. Ernsting and Fabrizio Santoro

Physical Chemistry Chemical Physics 2012 vol. 14(Issue 38) pp:13350-13364

Publication Date(Web):17 Jul 2012

DOI:10.1039/C2CP41522D

The photoisomerisation of 1,1′-diethyl-2,2′-pyridocyanine, regarded by Brooker as the simplest cyanine, is examined in methanol by time-resolved experiments and PCM/TD-CAM-B3LYP calculations. Femtosecond transient absorption, fluorescence upconversion, and stimulated Raman scattering, all with broadband coverage, provide a panoramic view of the photoreaction. On the computational side, evolving distributions on an S1 minimum-energy path are obtained by solving the Smoluchowski equation for drift and diffusion of torsional motion. Absorption and fluorescence bandshapes are calculated and compared to the observations; near-quantitative agreement implies that the entire S1 path has been observed. Most importantly the global S1 minimum, i.e. the perpendicular “phantom state” P*, can be identified and characterized in this way. Internal conversion of P* (3.7 ps), assisted by solvent equilibration, leads to the hot ground state. Within 5 ps, vibrational bands of cis and trans isomers are recognized with the help of calculated Raman spectra. The differences between observed and simulated spectra are discussed.

7-Amino-dibenzofuran-3-carboxylate: A new probe for femtosecond dynamic microsolvation studies of biomolecules

Co-reporter:Falko Berndt, Ilya Ioffe, Alexander A. Granovsky, Rainer Mahrwald, Sebastian Tannert, Sergey A. Kovalenko, Nikolaus P. Ernsting

Journal of Photochemistry and Photobiology A: Chemistry 2012 Volume 234() pp:164-170

Publication Date(Web):15 April 2012

DOI:10.1016/j.jphotochem.2012.02.015

Polar solvation dynamics in water and methanol: search for molecularity

Co-reporter:Mohsen Sajadi, Michael Weinberger, Hans-Achim Wagenknecht and Nikolaus P. Ernsting

Physical Chemistry Chemical Physics 2011 vol. 13(Issue 39) pp:17768-17774

Publication Date(Web):01 Sep 2011

DOI:10.1039/C1CP21794A

Time-dependent Stokes shifts (TDSS) were measured for diverse polarity probes in water, heavy water, methanol, and benzonitrile, by broadband fluorescence up-conversion with 85 fs time resolution. In water the spectral dynamics is solute-independent and quantitatively described by simple dielectric continuum theory of solvation. In methanol the slower part of the TDSS is solute-dependent. A correlation with anisotropy decay suggests that methanol solvation dynamics is modulated by orientational solute diffusion. An empirical power law which links the solvation relaxation function of a mobile solute to that of an immobile solute is experimentally verified. Activation energies for the average relaxation rate are also given. Solvation dynamics in H2O and D2O are identical at and above 20 °C but diverge below.

Photoisomerization around a Fulvene Double Bond: Coherent Population Transfer to the Electronic Ground State?

Co-reporter:Dr. Ilya Ioffe;Dr. Alexer L. Dobryakov;Dr. Alexer A. Granovsky;Dr. Nikolaus P. Ernsting;Dr. J. Luis Pérez Lustres

ChemPhysChem 2011 Volume 12( Issue 10) pp:1860-1871

Publication Date(Web):

DOI:10.1002/cphc.201001082

Abstract

Photoisomerization around a central fulvene-type double bond is known to proceed through a conical intersection at the perpendicular geometry. The process is studied with an indenylidene–dihydropyridine model compound, allowing the use of visible excitation pulses. Transient absorption shows that 1) stimulated emission shifts to the red and loses oscillator strength on a 50 fs timescale, and 2) bleach recovery is highly nonexponential and not affected by solvent viscosity or methyl substitution at the dihydropyridine ring. Quantum-chemical calculations are used to explain point 1 as a result of initial elongation of the central CC bond with mixing of S₂ and S₁ states. From point 2 it is concluded that internal conversion of S₁S₀ does not require torsional motion to the fully perpendicular state. The S₁ population appears to encounter a sink on the torsional coordinate before the conical intersection is reached. Rate equations cannot model the observed ground-state recovery adequately. Instead the dynamics are best described with a strongly damped oscillatory contribution, which could indicate coherent S₁–S₀ population transfer.

Detection of DNALigand Binding Oscillations by Stokes-Shift Measurements

Co-reporter:Mohsen Sajadi;Dr. Kristina E. Furse;Xin-Xing Zhang;Lars Dehmel;Dr. Sergey A. Kovalenko;Dr. Steven A. Corcelli;Dr. Nikolaus P. Ernsting

Angewandte Chemie International Edition 2011 Volume 50( Issue 40) pp:9501-9505

Publication Date(Web):

DOI:10.1002/anie.201102942

Femtosecond Stimulated Raman Spectroscopy of Flavin after Optical Excitation

Co-reporter:A. Weigel, A. Dobryakov, B. Klaumünzer, M. Sajadi, P. Saalfrank, and N. P. Ernsting

The Journal of Physical Chemistry B 2011 Volume 115(Issue 13) pp:3656-3680

Publication Date(Web):March 16, 2011

DOI:10.1021/jp1117129

In blue-light photoreceptors using flavin (BLUF), the signaling state is formed already within several 100 ps after illumination, with only small changes of the absorption spectrum. The accompanying structural evolution can, in principle, be monitored by femtosecond stimulated Raman spectroscopy (FSRS). The method is used here to characterize the excited-state properties of riboflavin and flavin adenine dinucleotide in polar solvents. Raman modes are observed in the range 90−1800 cm−1 for the electronic ground state S0 and upon excitation to the S1 state, and modes >1000 cm−1 of both states are assigned with the help of quantum-chemical calculations. Line shapes are shown to depend sensitively on resonance conditions. They are affected by wavepacket motion in any of the participating electronic states, resulting in complex amplitude modulation of the stimulated Raman spectra. Wavepackets in S1 can be marked, and thus isolated, by stimulated-emission pumping with the picosecond Raman pulses. Excited-state absorption spectra are obtained from a quantitative comparison of broadband transient fluorescence and absorption. In this way, the resonance conditions for FSRS are determined. Early differences of the emission spectrum depend on excess vibrational energy, and solvation is seen as dynamic Stokes shift of the emission band. The nπ* state is evidenced only through changes of emission oscillator strength during solvation. S1 quenching by adenine is seen with all methods in terms of dynamics, not by spectral intermediates.

Excited Stilbene: Intramolecular Vibrational Redistribution and Solvation Studied by Femtosecond Stimulated Raman Spectroscopy

Co-reporter:A. Weigel and N.P. Ernsting

The Journal of Physical Chemistry B 2010 Volume 114(Issue 23) pp:7879-7893

Publication Date(Web):May 19, 2010

DOI:10.1021/jp100181z

Excited-state relaxation of cis- and trans-stilbene is traced with femtosecond stimulated Raman spectroscopy, exploiting Sn ← S1 resonance conditions. For both isomers, decay in Raman intensity, shift of spectral positions, and broadening of the bands indicate intramolecular vibrational redistribution (IVR). In n-hexane this process effectively takes 0.5−0.7 ps. Analysis of the intensity decay allows us to further distinguish two phases for trans-stilbene: fast IVR within a subset of modes (∼0.3 ps) followed by slower equilibration over the full vibrational manifold (∼0.9 ps). In acetonitrile IVR completes with 0.15 ps; this acceleration may originate from symmetry breakage induced by the polar solvent. Another process, dynamic solvation by acetonitrile, is seen as spectral narrowing and characteristic band shifts of the C═C stretch and phenyl bending modes with 0.69 ps. Wavepacket motion is observed in both isomers as oscillation of low-frequency bands with their pertinent mode frequency (90 or 195 cm−1 in trans-stilbene; 250 cm−1 in cis-stilbene). Anharmonic coupling shows up as a modulation of high-frequency peak positions by phenyl/ethylene torsion modes of 57 and 90 cm−1. Decay and shift of the 90 cm−1 inverse Raman band within the first 0.3 ps suggests a gradual involvement of phenyl/ethylene torsion in relaxation. In cis- and trans-stilbene, low-frequency spectral changes are found within 0.15 ps, indicating an additional ultrafast process.

Terahertz Absorption Spectroscopy of a Liquid Using a Polarity Probe: A Case Study of Trehalose/Water Mixtures

Co-reporter:Mohsen Sajadi;Yathrib Ajaj;Ilya Ioffe Dr.;Hermann Weingärtner ;NikolausP. Ernsting

Angewandte Chemie International Edition 2010 Volume 49( Issue 2) pp:454-457

Publication Date(Web):

DOI:10.1002/anie.200904997

2-Aminopurine Incorporation Perturbs the Dynamics and Structure of DNA

Co-reporter:André Dallmann Dr.;Lars Dehmel;Torben Peters;Clemens Mügge Dr.;Christian Griesinger Dr.;Jennifer Tuma Dr.;NikolausP. Ernsting Dr.

Angewandte Chemie International Edition 2010 Volume 49( Issue 34) pp:5989-5992

Publication Date(Web):

DOI:10.1002/anie.201001312

Dynamic Polar Solvation Is Reported by Fluorescing 4-Aminophthalimide Faithfully Despite H-Bonding

Co-reporter:Mohsen Sajadi, Thorsten Obernhuber, Sergey A. Kovalenko, Manuel Mosquera, Bernhard Dick and Nikolaus P. Ernsting

The Journal of Physical Chemistry A 2009 Volume 113(Issue 1) pp:44-55

Publication Date(Web):December 15, 2008

DOI:10.1021/jp807605b

Solvation dynamics of 4-aminophthalimide (4AP) in methanol is measured by broadband upconversion of the fluorescence band. The peak emission frequency ν̃(t) is determined from 100 fs onward with 85 fs time resolution. Polar solvation based on simple continuum theory, including solute polarizability, describes the temporal shape of ν̃(t) quantitatively. Extrapolation ν̃(t→0) points to an initial emission frequency which agrees with the result from stationary spectroscopy in a nonpolar solvent. The extent (4300 cm−1) of the dynamic Stokes shift is largely due (50%) to H-bonding, however. The observations imply that H-bonds with 4AP adiabatically follow the dielectric relaxation of the methanol network. The stimulated emission band is also used to measure solvation dynamics. The evolving band is monitored by transient absorption spectroscopy of supercontinuum probe pulses. But the excited-state absorption spectrum, its relative amplitude, and its evolution are needed to extract ν̃(t) from such measurements. These key data are obtained by comparison with the upconversion results. Thus calibrated photometrically, 4AP transient absorption can be used to monitor solvation dynamics in any solvent. The excited-state absorption spectrum is assigned with the help of time-dependent density-functional calculations. Fluorescence excitation and double-resonance spectroscopy of isolated 4AP, cooled in a supersonic jet, is used to determine optically active modes. An intramolecular reorganization energy is inferred which is consistent with the value in 2-methylbutane (2025 cm−1). The crystal structure is also provided.

Local THz Time Domain Spectroscopy of Duplex DNA via Fluorescence of an Embedded Probe

Co-reporter:André Dallmann, Matthias Pfaffe, Clemens Mügge, Rainer Mahrwald, Sergey A. Kovalenko and Nikolaus P. Ernsting

The Journal of Physical Chemistry B 2009 Volume 113(Issue 47) pp:15619-15628

Publication Date(Web):September 18, 2009

DOI:10.1021/jp906037g

We demonstrate that THz vibrational activity of a biopolymer can be measured locally, on the effective length scale for polar solvation, with an embedded molecular probe. For this purpose, the polarity probe 2-hydroxy-7-nitrofluorene was linked into a 13mer DNA duplex opposite an abasic site. The NMR solution structure shows that the fluorene moiety occupies a well-defined position in place of a base pair but can flip around the long axis on a millisecond time scale. Femtosecond optical pump−probe experiments are used to measure the time-resolved Stokes shift of emission from the probe. The dynamic shifts for solution in H2O and D2O are quantified. Their difference is much larger than that expected for free water, implying that only bound water is observed. A weak 26 cm−1 spectral oscillation of the emission band is observed, which is not present when the probe is free in solution and is therefore caused by the supramolecular structure (DNA and hydration water).

Sub-picosecond fluorescence evolution of amino-cyano-stilbenes in methanol: polar solvation obeys continuum theory without evidence of twisting

Co-reporter:Nikolaus P. Ernsting, Jens Breffke, Dmitry Yu. Vorobyev, David A. Duncan and Inga Pfeffer

Physical Chemistry Chemical Physics 2008 vol. 10(Issue 15) pp:2043-2049

Publication Date(Web):19 Feb 2008

DOI:10.1039/B717541H

The spectral evolution of fluorescence from 4-(dimethylamino)-4′-cyanostilbene (DCS) in methanol, and of two derivatives bearing either the anilino (ACS) or the julolidino (JCS) moiety, was measured by optical Kerr-gating with a time resolution of 0.35 ps. A special thin Glan polariser in the Kerr shutter allows high contrast without unnecessarily increasing the group delay dispersion. The emission band may thus be gated and observed even with highly fluorescent samples. The spectral dynamics consists of a continuous red-shift and narrowing with similar relaxation behavior throughout, i.e. between these two observables and the three compounds. This suggests that polar solvation is the common cause for spectral relaxation after 0.2 ps. The continuum model describes the dynamic Stokes shift quantitatively. Contrary to previous reports we do not find a temporary isosbestic point in the fluorescence of JCS, nor is there evidence for a dependence on anilino substituents. The crystal structures of DCS and JCS are provided.

Femtosecond fluorescence spectroscopy by upconversion with tilted gate pulses

Co-reporter:Lijuan Zhao, J. Luis Pérez Lustres, Vadim Farztdinov and Nikolaus P. Ernsting

Physical Chemistry Chemical Physics 2005 vol. 7(Issue 8) pp:1716-1725

Publication Date(Web):16 Mar 2005

DOI:10.1039/B500108K

Time-resolved emission bands can be observed by simultaneous sum-frequency mixing with femtosecond near-infrared gate pulses over a wide frequency range. Using tilted gate pulses in a noncollinear geometry we achieve 80 fs time resolution and background-free measurement of upconverted spectra. All components were optimized resulting in a spectrometer for routine applications. As example we report the initial fluorescence from Coumarin 153 in acetonitrile after excitation at 400 nm. The fluorescence is modulated by nuclear coherence in the excited state which affects band width and asymmetry more than the energy gap itself.

Ultraschnelle Solvatation von N-Methyl-6-chinolon: eine Sonde für das lokale IR-Spektrum

Co-reporter:J. Luis Pérez Lustres Dr.;Sergey A. Kovalenko Dr.;Manuel Mosquera ;Tamara Senyushkina Dr.;Wolfgang Flasche

Angewandte Chemie 2005 Volume 117(Issue 35) pp:

Publication Date(Web):1 AUG 2005

DOI:10.1002/ange.200501397

Ein molekulares Dipolfeld (siehe Bild) wird durch Femtosekunden-Anregung der Titelverbindung erzeugt, und die Antwort der Umgebung wird über die stimulierte Emission des Farbstoffs beobachtet. Eine starke Frequenzmodulation der dynamischen Stokes-Verschiebung spiegelt kohärente Kernschwingungen der Solvathülle wider. Das IR-Spektrum des Lösungsmittels erklärt die Beobachtungen quantitativ im Rahmen der dielektrischen Kontinuumstheorie.

Ultrafast Solvation of N-Methyl-6-quinolone Probes Local IR Spectrum

Co-reporter:J. Luis Pérez Lustres Dr.;Sergey A. Kovalenko Dr.;Manuel Mosquera ;Tamara Senyushkina Dr.;Wolfgang Flasche

Angewandte Chemie International Edition 2005 Volume 44(Issue 35) pp:

Publication Date(Web):1 AUG 2005

DOI:10.1002/anie.200501397

A molecular dipole field (see picture) is created by femtosecond excitation of the title compound, and the response of the environment is observed by stimulated emission spectroscopy of the dye. Strong frequency modulation in the dynamic Stokes shift reflects coherent solvent motion. The IR spectrum of the solvent is related quantitatively to the experiment by dielectric continuum theory.

Cover Picture: ChemPhysChem 5/2002

Co-reporter:Stephan Hess;William B. Davis ;Alexer A. Voityuk Dr.;Notker Rösch ;Maria E. Michel-Beyerle ;Sergeij A. Kovalenko Dr.;J. Luis Pérez Lustres Dr.

ChemPhysChem 2002 Volume 3(Issue 5) pp:

Publication Date(Web):8 MAY 2002

DOI:10.1002/1439-7641(20020517)3:5<385::AID-CPHC385>3.0.CO;2-0

The cover picture shows an acridine derivative (ACMA) intercalated at an abasic site between nucleobases in B-DNA. Unlike the Stokes shift on the nanosecond time scale reported for this chromophore in polar solvents, dynamic solvation of ¹(ACMA)* in DNA occurs within 200 fs. The absence of slow relaxation components has been shown to be important for the mechanism of the photoinduced oxidation of distant guanine molecules. Besides this mechanistic issue, excited-state dynamics of chromophores bound to DNA are most relevant for their application in sequencing and genomic chip technologies.

Excited-State Photophysics of an Acridine Derivative Selectively Intercalated in Duplex DNA

Co-reporter:Stephan Hess;William B. Davis ;Alexer A. Voityuk Dr.;Notker Rösch ;Maria E. Michel-Beyerle ;Sergeij A. Kovalenko Dr.;J. Luis Pérez Lustres Dr.

ChemPhysChem 2002 Volume 3(Issue 5) pp:

Publication Date(Web):8 MAY 2002

DOI:10.1002/1439-7641(20020517)3:5<452::AID-CPHC452>3.0.CO;2-K

Faster than 200 fs is the time scale of dynamic solvation of an acridine derivative (ACMA) intercalated into an abasic site of the DNA duplex. This observation implies that the Stokes shift of 0.41 eV is due to ultrafast repolarization of the nuclear degrees of freedom of the DNA pocket. In this system, the environmental reorganization induced by the dipole moment change of 3–4 Debye upon excitation may involve both π–π interactions between ACMA and the adjacent nucleobases as well as polar interactions exerted by the hydrogen bonds of these base pairs.

Isosteric and fluorescent DNA base pair formed by 4-amino-phthalimide and 2,4-diaminopyrimidine: melting, structure, and THz polar solvation dynamics

Co-reporter:L. Dehmel, F. Berndt, M. Weinberger, M. Sajadi, I. Ioffe, H.-A. Wagenknecht and N. P. Ernsting

Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 9) pp:NaN6820-6820

Publication Date(Web):2016/02/09

DOI:10.1039/C5CP06972F

Sub-picosecond fluorescence evolution of amino-cyano-stilbenes in methanol: polar solvation obeys continuum theory without evidence of twisting

Co-reporter:Nikolaus P. Ernsting, Jens Breffke, Dmitry Yu. Vorobyev, David A. Duncan and Inga Pfeffer

Physical Chemistry Chemical Physics 2008 - vol. 10(Issue 15) pp:NaN2049-2049

Publication Date(Web):2008/02/19

DOI:10.1039/B717541H

Polar solvation dynamics in water and methanol: search for molecularity

Co-reporter:Mohsen Sajadi, Michael Weinberger, Hans-Achim Wagenknecht and Nikolaus P. Ernsting

Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 39) pp:NaN17774-17774

Publication Date(Web):2011/09/01

DOI:10.1039/C1CP21794A

Dual-fluorescence pH probe for bio-labelling

Co-reporter:C. Richter, C. Schneider, M. T. Quick, P. Volz, R. Mahrwald, J. Hughes, B. Dick, U. Alexiev and N. P. Ernsting

Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 45) pp:NaN30597-30597

Publication Date(Web):2015/10/19

DOI:10.1039/C5CP05454K

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