Medium Effects on the Rates of Stereomutation of a Pair of Diastereomeric Cyclopropanones. Ground State Stabilization in Nucleophilic Solvents Induces Deviation from Solvent Polarity Controlled Behavior

1996 ◽  
Vol 118 (26) ◽  
pp. 6241-6251 ◽  
Author(s):  
Matthew H. J. Cordes ◽  
Jerome A. Berson
Keyword(s):  
Ground State ◽  
Solvent Polarity ◽  
Medium Effects

scholarly journals Studies on Photophysical Properties of Mono-carbonyl Curcumin Analogues: Experimental and Theoretical approach

2018 ◽  
Vol 34 (4) ◽  
pp. 2170-2179
Author(s):  
Manjula Rayanal ◽  
Prasad Pralhad Pujar ◽  
Sridhar D
Keyword(s):  
Excited State ◽  
Ground State ◽  
Dipole Moments ◽  
Photophysical Properties ◽  
Stokes Shift ◽  
Solvent Polarity ◽  
Frontier Molecular Orbital ◽  
Curcumin Analogues ◽  
Td Dft ◽  
Ground State Dipole Moments

The solvatochromic fluorescence behaviour of mono-carbonyl curcumin analogues has been studied in ten different solvents ranging from non-polar to polar. The solvent effect on the spectral properties of analogues has been discussed. The ground state dipole moments were estimated experimentally by Bilot-Kawski equation which is a function of Stokes shift with the solvent polarity parameters and Guggenheim method and theoretically by TD-DFT studies. The excited state dipole moment was determined using Bilot-Kawski equations. The excited state dipole moments for the two molecules were found to be higher than their corresponding ground state dipole moments. Theoretically Frontier molecular orbital (HOMO/ LUMO) energies were determined by Gaussian 09 W software using TD-DFT.

Die Lösungsmittelabhängigkeit der thermischen cis-trans-Isomerisierung von N-Benzylidenanilinen mit Donator/Akzeptor-Substituenten.

1976 ◽  
Vol 31 (7) ◽  
pp. 953-959 ◽  
Author(s):  
U. Berns ◽  
G. Heinrich ◽  
H. Gusten
Keyword(s):  
Ground State ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Solvent Polarity ◽  
Linear Functions ◽  
Aryl Group ◽  
Trans Isomerization ◽  
Solvatochromic Shifts ◽  
Z Value ◽  
Inversion Mechanism

Thermal cis →-trans isomerization of eight N-benzylideneanilines with donor and/or acceptor substituents in the para, para'-positions was studied in different solvents by observing the rapid relaxation to the thermodynamic stable trans isomer following flash photolysis. With the push-pull effect of the substituents in the direction of the N-aryl group the rate constant at 25°C is by three powers of 10 faster compared to the N–benzylideneaniline with opposite arrangement of substituents. The rate constants are independent of the nature of the substituents in the para-position of the benzylidene group. The rate constants of N-(4-nitrobenzylidene)-p-anisidine are linear functions of the solvent polarity scale based on solvatochromic shifts (Kosowers Z-value or Dimroths ET-value). With increasing push-pull effect of the substituents in the direction of the N-aryl group the rate constants do no longer depend on the polarity of the solvent. The observed solvent effects on the rates and the activation energies for thermal cis→ trans isomerization suggest that the transition state of the reaction is less polar than the ground state of the sterically hindered cis-N-benzylideneaniline, thus favouring an inversion mechanism to become operative with respect to the N-benzylideneanilines.

CHAMELEON GROUND STATE AND EXCITED STATES OF EDT-TTF-IM-F4TCNQ RADICAL DYAD IN DIFFERENT ENVIRONMENTS

2012 ◽  
Vol 11 (03) ◽  
pp. 505-525 ◽  
Author(s):  
YUHUA ZHOU ◽  
KAI TAN ◽  
XIN LU
Keyword(s):  
Charge Transfer ◽  
Solid State ◽  
Excited States ◽  
Ground State ◽  
Density Functional ◽  
Solvent Polarity ◽  
Functional Study ◽  
Polar Solvents ◽  
Model Calculations ◽  
A Charge

We have performed a systematic density functional study on the ground-state electronic structure and excited states of a representative D-σ-A dyad, i.e. EDT-TTF-Im-F4TCNQ π-radical, in vacuo and in different conventional solvents (toluene, THF, DMF and DMSO) by using some popular hybrid density functionals (B3LYP, M05, M05-2X, PBE0 and BMK). It has been shown that the M05 and B3LYP functionals perform the best in predicting the intramolecular charge-transfer (ICT) pertaining to both the ground state and excited states of the dyad. The amphoteric dyad is liable to solvent-promoted ICT from its EDT-TTF-Im donor (D) to F4TCNQ acceptor (A), adopting a charge-unseparated ground state D-A• in vacuo, a partially zwitterionic ground state [D-A]• in nonpolar toluene solvent, and a fully zwitterionic ground state D•+-A- in such polar solvents as THF, DMF and DMSO. Owing to its solvent-dependent chameleon ground state, excited states of the dyad in solvents also exhibit remarkable dependence on solvent polarity, as revealed by TDDFT calculations. Furthermore, cluster model calculations revealed that intermolecular charge-transfer readily occurs between the dyads, accounting for the observed zwitterionic charge state in solid state and solid-state semiconductivity.

scholarly journals A semi-empirical estimation of ground and excited state dipole moments of zinc phthalocyanine from solvatochromic shift data

2018 ◽  
Vol 6 (2) ◽  
pp. 190
Author(s):  
Abimbola Ogunsipe
Keyword(s):  
Excited State ◽  
Ground State ◽  
Dipole Moments ◽  
Solvent Polarity ◽  
Zinc Phthalocyanine ◽  
Empirical Estimation ◽  
Solvatochromic Shift ◽  
Excited State Dipole Moments ◽  
Semi Empirical ◽  
Ground State Dipole Moments

A semi-empirical determination of ground and excited state dipole moments of zinc phthalocyanine (ZnPc) from solvatochromic shifts is hereby presented. The ratio of the excited- and ground-state dipole moments of ZnPc ( ) was estimated by a combination of the Bakshiev and the Kawski-Chamma-Viallet’s equations, while the difference in the excited- and ground-state dipole moments (Dm) was estimated usingthe molecular-microscopic solvent polarity parameters ( ), alongside the Stokes’ shifts (Dῡ) in the various solvents. The dipole moment of ZnPc is significantly higher in the excited singlet state (me = 3.12 D) than in the ground state (mg = 1.50 D). Obviously charge separation is greater in the excited state of ZnPc than in its ground state.  

Dipole moments and quenching of fluorescence of a new coumarin dye

2020 ◽  
Vol 98 (8) ◽  
pp. 761-769
Author(s):  
Omnath Patil ◽  
P.K. Ingalagondi ◽  
Shivaraj Gounhalli ◽  
S.M. Hanagodimath
Keyword(s):  
Activation Energy ◽  
Excited State ◽  
Ground State ◽  
Density Functional ◽  
Dipole Moments ◽  
Fluorescence Emission ◽  
Solvent Polarity ◽  
Chemical Hardness ◽  
Fluorescence Emission Spectra ◽  
Coumarin Dye

The absorption and fluorescence emission spectra of a newly synthesized laser grade coumarin dye, 1-((4-methoxyphenoxy) methyl)-3H-benzo[f]chromen-3-one (4-MPMBC), have been recorded in various solvents having different polarities. The spectrum peak was found to shift toward a higher wavelength with an increase in the solvent polarity. The dipole moments of the ground state (μg) and excited state (μe) were estimated using the Lippert, Bakshiev, and Kawski–Chamma–Viallet equations. The μe values were found to be greater than the μg values in all solvents, indicating that the dye is more polar in the excited state than in the ground state. The absorption maximum and emission maximum energies, ground- and excited-state dipole moments, and HOMO–LUMO energy gaps were estimated using Gaussian 16W. These have been compared with the experimental results. The estimated chemical hardness of the dye molecule indicates the soft nature in all of the solvents. The reactive centers such as nucleophilic and electrophilic sites were identified along with contour action using electrostatic potential three-dimensional map density functional theory analysis. The fluorescence quenching has been studied in solvents of varying polarities using aniline as a quencher. The quenching process was found to follow the Stern–Volmer equation and was studied by considering the role of diffusion. In all solvents, the probability of quenching per encounter (p) was found to be less than unity. The activation energy for diffusion and activation energy for quenching were estimated using the values of p.

scholarly journals Effect of solvent polarity on the photophysical properties of chalcone derivatives

RSC Advances ◽  
2017 ◽  
Vol 7 (39) ◽  
pp. 24204-24214 ◽  
Author(s):  
Rekha Kumari ◽  
Anitha Varghese ◽  
Louis George ◽  
Sudhakar Y. N.
Keyword(s):  
Excited State ◽  
Organic Solvents ◽  
Ground State ◽  
Photophysical Properties ◽  
Solvent Polarity ◽  
Chalcone Derivatives ◽  
Effect Of Solvent

The photophysical properties were studied for FNPO, AFPO and FHPO in different organic solvents. The excited state of the molecules were found to be more polar than the ground state.

scholarly journals Estimating the Ground and Excited State Dipole Moments of Levofloxacin and Norfloxacin Drugs Using Solvatochromic Effects and Computational Work

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Kinfe Woldegiorges ◽  
Abebe Belay ◽  
Alemu Kebede ◽  
Tamirat Abebe
Keyword(s):  
Excited State ◽  
Ground State ◽  
Dipole Moments ◽  
Bacterial Species ◽  
Emission Spectra ◽  
Solvent Polarity ◽  
Electron Charge Density ◽  
Nonpolar Solvents ◽  
Computational Work ◽  
Excited State Dipole Moments

Levofloxacin (LVF) and norfloxacin (NRF) are a group of fluoroquinolone antibiotics, broad spectrum used to treat various infections caused by many bacterial species. The drugs contain functional groups which control the type and degree of interaction with different solvents. In this research, the ground and excited state dipole moments of LVF and NRF drugs were estimated using solvatochromic effects and computational work. The dipole moments were estimated from absorption and emission spectra in polar and nonpolar solvents using Bakhshiev’s, Kawski–Chamma–Viallet, Lippert–Mataga, and Reichardt models. The results indicated the emission spectra are more strongly affected by solvent polarity than the absorption spectra. The calculated excited state dipole moment is larger than that of the ground state, indicating that the probe compounds are significantly more polarized in the excited state than in the ground state. From computational work, the HOMO-LUMO energy band gap, the dipole moments, electron charge density distribution, and oscillator strength were determined using the semiempirical MP6 method, DFT-B3LYP-6-31G, and DFT-B3LYP-3-21G employing Gaussian 09 software. In general, larger dipole moments were obtained by computation rather than from experiments due to the absence of solvent effects.

scholarly journals Resolving photoisomerization dynamics via ultrafast UV-visible transient absorption spectroscopy

2021 ◽  
Author(s):  
◽  
Shyamal Prasad
Keyword(s):  
Absorption Spectroscopy ◽  
Ground State ◽  
Transient Absorption ◽  
Bond Cleavage ◽  
Ultra Violet ◽  
Solvent Polarity ◽  
Transient Absorption Spectroscopy ◽  
Bond Breakage ◽  
Solvent Dependence ◽  
Azobenzene Moiety

<p>Transient absorption spectroscopy has been employed to investigate three photo–active compounds; azobenzene, foldamer controlled by azobenzene, and oxazine. These compounds all have absorption in the ultra–violet regions responsible for their photo–active behavior. Due to this, the current transient absorption setup has been modified to extend the probing wavelength range to 320–650 nm, with the possibility of exciting the photo–active molecule in the ultra–violet.  Azobenzene is valuable in benchmarking and optimizing the transient absorption setup, it shows that the detection window has been extended out to 320 nm. By resolving the ground state bleach we have added support for the assignment of the final decay to thermalization in the ground state. Comparison of relaxation lifetime in acetonitrile and tetrahydrofuran shows no noticeable change in the photophysics of isomerization between the two solvents.  The foldamer family excited state relaxation is similar to azobenzene. There is an extension in the S₁ branching lifetime from 1.1 ps in azobenzene to 1.7 ps for foldamer 1 and 4.2 ps for foldamer 2. The separation of branching on the S₁ surface and relaxation through the S₁ to electronic ground state intersection was possible by comparison of azobenzene and foldamer family. The solvent effects show little difference for all members of the foldamer family expect for foldamer 2, suggesting that the dynamics of the azobenzene moiety are not affected by the larger macro–structure of the foldamer.  For oxazine it has been established, by varying solvent polarity, that isomerization happens through three states; bond breakage, transfer to a dark state, and the final photo–isomer. This is confirmed by further studies completed after the introduction of electron withdrawing fluorine atoms. Carbon–oxygen bond cleavage occurs on the picosecond timescale, with solvent dependent rotation occurring in hundreds of picoseconds. Fluorinated oxazine shows a strong solvent dependence with rotation suppressed for all but the most polar of solvents.</p>

Structural Studies of a Series of Organic Non-Linear Optical Materials

1997 ◽  
Vol 53 (5) ◽  
pp. 812-821 ◽  
Author(s):  
J. C. Cole ◽  
J. M. Cole ◽  
G. H. Cross ◽  
M. Farsari ◽  
J. A. K. Howard ◽  
...  
Keyword(s):  
Crystal Structures ◽  
Ground State ◽  
Optical Materials ◽  
Dipole Moments ◽  
Solvent Polarity ◽  
Structural Studies ◽  
Acta Cryst ◽  
X Ray ◽  
Solution State ◽  
X Ray Crystallography

The crystal structures of {4-[bis(diethylamino)methylium]phenyl}dicyanomethanide (I), {4-[cyano(4-methylpiperidyl)methylium]phenyl } dicyanomethanide (II), {4-[cyano(1-pyrrolidinyl)methylium]phenyl}dicyanomethanide (IV) and (Z)-{4-[1,3-dicyano-3-(diethylamino)-2-propenylium]phenyl} dicyanomethanide have been determined by X-ray crystallography. Together with (Z)-{4-[1-cyano-3-(diethylamino)-2-propenylium]phenyl}dicyanomethanide [(III): Cole, J. C., Howard, J. A. K., Cross, G. H. & Szablewski, M. (1995). Acta Cryst. C51, 715–718], these compounds exhibit varying degrees of quinoidal characteristics and yet have predominantly zwitterionic ground state character. The presence of high dipole moments in the crystal can thus be inferred and are substantiated by measurements of high solution-state dipole moments. Negative solvatochromism (hypsochromism on increasing solvent polarity) confirms the zwitterionic character in at least two of the series.

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