State In Polar Solvents Research Articles

Phosphorescence characteristics of acetophenone, benzophenone, p-aminobenzophenone and michlercs ketone in various environments

The phosphorescence characteristics (excitation and emission spectra and lifetimes) of acetophenone (AP), benzophenone (BP), p-aminobenzophenone (PABP) and Michler's ketone (MK) adsorbed on Whatman No. 1 filter paper were measured at various temperatures, and compared with the phosphorescence characteristics in different solvent glasses at 77 K. Both AP and BP phosphoresce on filter paper only at low temperature (208 K). The phosphorescence lifetimes of AP and BP are < 1 msec, indicating a 3( n,π ∗) lower triplet level for paper substrates. With PABP, the low lying triplet state in polar solvents is 3(CT) and in non-polar solvents is 3( n, π ∗); PABP on filter paper results in spectral characteristics similar to those of PABP in polar solvents at 77 K. The lifetime of PABP is longer than that of BP, indicating a 3(CT) low-lying triplet state. MK, like PABP, has strongly environment-dependent photophysical properties. MK, when adsorbed on filter paper, has an intense long-lived luminescence at room temperature, resulting in a limit of detection of 3 ng ml or 3 pg, and a linear dynamic range of over 3 orders of magnitude. MK appears to be strongly hydrogen-bonded to the filter paper. In studies in ethanol and other solvents, MK adsorbed on filter paper shows a dramatic change in its phosphorescence spectrum when the temperature is lowered from 298 K to 208 K; the phosphorescence peak moves to longer wavelengths and the intensity decreases. The temperature effect could arise from the presence of several conformers of MK or be due to different environmental sites or E-type delayed fluorescence. The low-lying triplet state of MK on filter paper is most likely a 3(CT) state. Lowering the temperature appears to increase the phosphorescence intensity for ketones which phosphoresce in the 3( n,π ∗) triplet state, but affects it only slightly for analytes which phosphoresce in the 3(π,π ∗) triplet state. Room-temperature phosphorescence seems to arise for aromatic ketones and aldehydes with low-lying 3(π, π ∗) or 3(CT) triplet states.

Fluorescence studies on solvent-induced intramolecular charge separation in symmetric biaryls

Fluorescence studies on 5,5′-bi-benz[a]-pyrenyl reveal that the emitting state in polar solvents possesses a high dipole moment. Even in non-polar solvents such as n-hexane, dual fluorescence is emitted, with a structured twisted intramolecular charge transfer band. This puts an upper limit to the dipolar solvent fluctuations necessary to induce symmetry reduction and charge separation in the excited state. Theoretical guidelines to predict further cases of biaryls that exhibit charge separation in the excited state are derived.

Solute–solvent exciplex versus twisted intramolecular charge-transfer state in anomalous fluorescence of 4-NN-dimethylaminobenzonitrile

We report on the influence which solvent deuteration and solute–solvent interactions in glassy matrices have on the fluorescence of 3,5,NN-tetramethyl-4-aminobenzonitrile and of 4-NN-dimethyl-aminobenzonitrile. The widely accepted assignment of the anomalous fluorescence of the latter compound to emission from a twisted intramolecular charge-transfer state does not explain the observations. It is pointed out that the large deuterium effect on the anomalous fluorescence may be understood in terms of the theory of radiationless electronic relaxation when the emission comes from a solute—solvent exciplex. Spectral shifts, which arise from coupling of solute electric dipole moments with the polarization of the surroundings, have been calculated for the case of a solute in a homogenous polar glassy matrix, relative to a solution in a non-polar glass. The shift found for the fluorescence of 3,5,NN-tetramethyl-4-aminobenzonitrile is not in agreement with acceptable values for molecular excited-state dipole moments. Emission from an exciplex is more in accordance with the shift. Because the amino group of 4-NN-dimethylaminobenzonitrile cannot rotate in glassy solutions, there is no exciplex emission from this compound in a polar glass. This does not exclude the formation of planar-solute exciplexes, which decay predominantly by a radiationless process. Our earlier suggestion concerning the formation of exciplexes with polar solvent molecules provides an adequate explanation of the facts for the decay of the first excited singlet states of 4-NN-dimethylaminobenzonitrile and related compounds. It may explain our observation of ion formation from these states in polar solvents, which occurs even when the amino group is restricted to be in plane with the phenyl ring and there is no anomalous fluorescence. We suggest that a planar-solute exciplex (E1) is the precursor of an emitting twisted-solute exciplex (E2). Then competition between ionic dissociation and rotational isomerization of E1 becomes an important factor, determining the quantum yield of anomalous fluorescence. A quantum chemical analysis of the consequences of overlap of atomic orbitals on the N atom of the amino group with lone-pair orbitals of the solvent molecule shows that both planar and twisted solute–solvent exciplex states may be bound states.

On the Basic Equation for the Equilibrium Electronic States in Polar Solvents –Broken Symmetry–

The basic equation to determine the equilibrium electronic structure ψ of the solute system (the solvated electron or the solute molecule or the solute molecular complex) in polar solvent is proposed in the form of variational equation δ( F t (ψ)-κ f )=0 which states that the free energy of the total system F t (ψ) consisting of the solute system and the solvent is minimum for an arbitrary variation of ψ in accordance with the normalization condition f = -1=0; here κ denotes a Lagrange undetermined multiplier. The nonlinear wave equations derived from the basic equation for the dimeric molecules or their radicals yield the broken symmetry solutions (self-trapping states). The simple description of the solvated electron is presented as another example of the application of the basic equation.

ChemInform Abstract: PHOTOELECTRON EJECTION AND FLUORESCENCE FROM MOLECULAR ′RYDBERG′ STATES IN POLAR SOLVENTS

Chemischer InformationsdienstVolume 7, Issue 19 Physical Organic Chemistry ChemInform Abstract: PHOTOELECTRON EJECTION AND FLUORESCENCE FROM MOLECULAR ′RYDBERG′ STATES IN POLAR SOLVENTS YOSHIHIRO NAKATO, YOSHIHIRO NAKATOSearch for more papers by this authorAKIHIRO NAKANE, AKIHIRO NAKANESearch for more papers by this authorHIROSHI TSUBOMURA, HIROSHI TSUBOMURASearch for more papers by this author YOSHIHIRO NAKATO, YOSHIHIRO NAKATOSearch for more papers by this authorAKIHIRO NAKANE, AKIHIRO NAKANESearch for more papers by this authorHIROSHI TSUBOMURA, HIROSHI TSUBOMURASearch for more papers by this author First published: May 11, 1976 https://doi.org/10.1002/chin.197619040AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue19May 11, 1976 RelatedInformation

Photoelectron Ejection and Fluorescence from Molecular “Rydberg” States in Polar Solvents

Abstract Absorption and fluorescence spectra and photo-current yield curves of tetraaminoethylenes are studied. The UV absorption of these compounds is mostly attributable to the transitions from the ground state to the “vertical” Rydberg-like and ionized states. Their spectral shapes in ether and in pentane are nearly coincident with each other, showing that these states just after excitation are little affected by the solvent polarity. Based on this result and the results of photo-current measurements, the spontaneous formation of free, solvated electrons from the “vertical” Rydberg-like states in polar solvents has been verified. It is also found that the maximum wave numbers, the lifetimes and the yields of the fluorescence from the lowest “relaxed” Rydberg-like state depend strongly on solvent polarity, temperature and rigidity. These results are explained by taking account of the competition between electron ejection and relaxation processes and of the presence of a non-fluorescent, solvated cation-electron pair. The photo-electron ejection from other organic molecules in polar solvents reported before is shown to be explained by the same scheme as presented here.

ChemInform Abstract: IONIC PHOTODISSOCIATION OF ELECTRON DONOR‐ACCEPTOR COMPLEXES

Ionic photodissociation of electron donor-acceptor (EDA) complexes of s-tetracyanobenzene (TCNB) and pyromellitic dianhydride (PMDA) with 2-methyltetrahydrofuran (MTHF) has been investigated by means of nsec flash photolysis and transient photocurrent measurements. The solvent-shared ion-pair of TCNB anion and MTHF cation is formed from the excited charge-transfer (CT) singlet state of a TCNB–MTHF complex, dissociating into solvated ions. TCNB complexes with aromatic hydrocarbons dissociate directly into ions from the lowest excited CT singlet state. Dissociation of PMDA complexes occurs in the CT triplet state in nonpolar solvents and mainly in the excited CT singlet state in polar solvents. The relative rate constant of radiationless process, which competes with ionic dissociation in the excited singlet state, can be deduced from the effect of solvent on ionic photodissociation. It has been confirmed for the first time that the ionic dissociation of a TCNB–benzene–1,2-dichloroethane (DCE) system occurs ...

Ionic Photodissociation of Electron Donor-Acceptor Complexes

Abstract Ionic photodissociation of electron donor-acceptor (EDA) complexes of s-tetracyanobenzene (TCNB) and pyromellitic dianhydride (PMDA) with 2-methyltetrahydrofuran (MTHF) has been investigated by means of nsec flash photolysis and transient photocurrent measurements. The solvent-shared ion-pair of TCNB anion and MTHF cation is formed from the excited charge-transfer (CT) singlet state of a TCNB–MTHF complex, dissociating into solvated ions. TCNB complexes with aromatic hydrocarbons dissociate directly into ions from the lowest excited CT singlet state. Dissociation of PMDA complexes occurs in the CT triplet state in nonpolar solvents and mainly in the excited CT singlet state in polar solvents. The relative rate constant of radiationless process, which competes with ionic dissociation in the excited singlet state, can be deduced from the effect of solvent on ionic photodissociation. It has been confirmed for the first time that the ionic dissociation of a TCNB–benzene–1,2-dichloroethane (DCE) system occurs in the excited Franck-Condon (FC) state. It is pointed out that the latter dissociation mechanism is not inconsistent with all the results obtained for TCNB and PMDA complexes under various conditions.

Theoretical Studies of Excess Electron States in Liquids

AbstractIn this paper an attempt will be made to review the current state of the art in our understanding of excess electron states in non polar and polar liquids, with an emphasis on the following problems: The nature of quasi free and localized excess electron states. Localization criteria. Energetic stability of the localized excess electron state. Nature of electron solvent interactions. Configurational charges in the medium. A brief survey of excess electron states in non polar solvents such as He, Ar, Kr, Xe, H2, and D2 will focus attention on the general stability problem of an excess electron in a non polar dense fluid, configurational diagrams in ground and excited states, optical properties and non radiative relaxation processes. The basic problems involved are identical with those encountered in the study of excess electron states in polar solvents.Excess electron states in polar solvents will be handled by the application of continuum and molecular models. Information will be presented concerning the quasi free excess electron state in polar solvents, the electronic and medium rearrangement energy for the cavity model, the configurational stability of ground and excited state, configurational diagrams, optical properties, optical lineshapes and relaxation phenomena.

Excess Electrons in Polar Solvents

In this paper we consider a structural model for localized excess electron states in polar solvents with particular reference to dilute metal ammonia solutions and to the hydrated electron. The over-all energetic stability of these species was assessed by considering simultaneously the electronic energy and the medium rearrangement energy. The present model consists of a finite number of loosely packed molecules on the surface of the cavity which are subjected to thermal fluctuations and a polarizable continuum beyond. The electronic energy was computed utilizing an electrostatic microscopic short-range attraction potential, a Landau-type potential for long-range interactions, and a Wigner-Seitz potential for short-range repulsive interactions. The medium rearrangement energy includes the surface tension work, the dipole–dipole repulsion in the first solvation layer, and most importantly the short-range repulsive interactions between the hydrogen atoms of the molecules oriented by the enclosed charge. The gross features of localized electron states in different solvents can be rationalized in terms of different contributions to the medium rearrangement terms. The energetic stability of the localized state of excess electrons in polar solvents was established and the cavity size in the ground state of the solvated electron could be uniquely determined. Experimental energetic and structural data such as volume expansion, coordination numbers, heats of solution, and spectroscopic properties are in qualitative agreement with the predictions of the present model. Optical line shape data calculated from the theoretical model do not agree with experiment; this discrepancy suggests that more data are required in regard to the excited states of the solvated electron.