Substituted N,N-dialkylanilines: relative ionization energies and proton affinities through determination of ion-molecule reaction equilibrium constants
Abstract:The relative ionization energies and proton affinities of AJV-dimethyl-, AyV-diethyl-, and AyV-di-n-propylaniline, and metaand para-methyl-substituted analogues (as well as AfJV,3,5-tetramethylaniline and 4-chloro-AT,Ardiethylaniline) have been determined in the gas phase through measurements of the equilibrium constants of charge-transfer and proton-transfer reactions in an ion cyclotron resonance spectrometer. Absolute values are assigned to the ionization energies and proton affinities generated in these ex… Show more
“…40 A lower-energy CT emission at 532 nm is observed for DEA guest molecules in 1b, which possess a reduced I(D) of 6.99 eV. 41 These observations are consistent with eqn (1), which establishes a rational and facile means for tuning the luminescence properties of these materials. It is also of interest to note the large spectral shift (150 nm) separating the monomer and CT emission maxima in 1b, which contrasts with the 40 nm separation observed for the exciplex formed between naphthalene and DEA.…”
One of the ongoing goals in the field of porous materials is the design and synthesis of materials that possess chemical structures amenable for use in sensing applications. We describe the preparation, luminescence characteristics, and environmental sensing properties of variants of the aluminum-based MOF [Al(OH)(O(2)C-C(10)H(6)-CO(2))](∞). Careful activation of the open framework complex, 1, yielded a dynamic structural transformation to a non-porous form, 2, that exhibited strong inter-linker interactions and red-shifted emission characteristics indicative of dimer formation. We also demonstrate the formation of highly luminescent ground-state charge-transfer (CT) complexes between 1 and the electron-donating amines dimethylamine (DMA) (1a), and N,N-diethylaniline (DEA) (1b), both of which exhibit dual-emission characteristics and a ratiometric luminescence response that is sensitive to temperature and solvent polarity. Steady-state and time-resolved measurements on 1a, 1b, and 2 indicate that the MOF structures stabilize ground-state CT interactions that are distinct from the weakly-bound exciplexes formed in comparable mixtures of purely organic components. The spectra for 1a and 1b also indicate different temperature dependencies that correspond to thermally-activated complex formation (ΔH(f) = +1.1 ± 0.2 kcal mol(-1)) in 1a and static quenching effects (ΔH(f) = -2.2 ± 0.3 kcal mol(-1)) in 1b. The addition of ethanol, isopropanol, toluene, or chloroform to suspensions of 1b indicate destabilization of the CT state with increasing solvent polarity, which suggests the generalized application of this or related materials in sensor applications.
“…40 A lower-energy CT emission at 532 nm is observed for DEA guest molecules in 1b, which possess a reduced I(D) of 6.99 eV. 41 These observations are consistent with eqn (1), which establishes a rational and facile means for tuning the luminescence properties of these materials. It is also of interest to note the large spectral shift (150 nm) separating the monomer and CT emission maxima in 1b, which contrasts with the 40 nm separation observed for the exciplex formed between naphthalene and DEA.…”
One of the ongoing goals in the field of porous materials is the design and synthesis of materials that possess chemical structures amenable for use in sensing applications. We describe the preparation, luminescence characteristics, and environmental sensing properties of variants of the aluminum-based MOF [Al(OH)(O(2)C-C(10)H(6)-CO(2))](∞). Careful activation of the open framework complex, 1, yielded a dynamic structural transformation to a non-porous form, 2, that exhibited strong inter-linker interactions and red-shifted emission characteristics indicative of dimer formation. We also demonstrate the formation of highly luminescent ground-state charge-transfer (CT) complexes between 1 and the electron-donating amines dimethylamine (DMA) (1a), and N,N-diethylaniline (DEA) (1b), both of which exhibit dual-emission characteristics and a ratiometric luminescence response that is sensitive to temperature and solvent polarity. Steady-state and time-resolved measurements on 1a, 1b, and 2 indicate that the MOF structures stabilize ground-state CT interactions that are distinct from the weakly-bound exciplexes formed in comparable mixtures of purely organic components. The spectra for 1a and 1b also indicate different temperature dependencies that correspond to thermally-activated complex formation (ΔH(f) = +1.1 ± 0.2 kcal mol(-1)) in 1a and static quenching effects (ΔH(f) = -2.2 ± 0.3 kcal mol(-1)) in 1b. The addition of ethanol, isopropanol, toluene, or chloroform to suspensions of 1b indicate destabilization of the CT state with increasing solvent polarity, which suggests the generalized application of this or related materials in sensor applications.
“…E CR increases linearly by increasing the electron-withdrawing properties of the donor ring substituent (IP D ) (Figure ). 5 Plot of the CR band energy ( E CR ) vs the difference in ionization potentials (IP D − IP A ) between 4-XC 6 H 4 CH 3 (IP D ) (taken from refs and ). and 4-CH 3 OC 6 H 4 CH 3 (IP A ) (8.18 eV, taken from ref ).…”
Section: Discussionmentioning
confidence: 99%
“…Plot of the CR band energy ( E CR ) vs the difference in ionization potentials (IP D − IP A ) between 4-XC 6 H 4 CH 3 (IP D ) (taken from refs and ). and 4-CH 3 OC 6 H 4 CH 3 (IP A ) (8.18 eV, taken from ref ).…”
Spectral properties and reactivities of ring-methoxylated diarylmethane and diarylmethanol radical cations, generated in aqueous solution by pulse and gamma-radiolysis and by the one-electron chemical oxidant potassium 12-tungstocobalt(III)ate, have been studied. The radical cations display three bands in the UV, visible, and vis-NIR regions of the spectrum. The vis-NIR band is assigned to an intramolecular charge resonance interaction (CR) between the neutral donor and charged acceptor rings, as indicated by the observation that the relative intensity of the vis-NIR band compared to that of the UV and visible bands does not increase with increasing substrate concentration and that the position and intensity of this band is influenced by the ring-substitution pattern. In acidic solution (pH = 4), monomethoxylated diarylmethanol radical cations 1a.(+ -)1e.(+) decay by C(alpha)-H deprotonation [k = (1.7-1.9) x 10(4)s(-1)] through the intermediacy of a ketyl radical, which is further oxidized in the reaction medium to give the corresponding benzophenones, as evidenced by both time-resolved spectroscopic and product studies. With the dimethoxylated radical cation 2.(+), C(alpha)-H deprotonation is instead significantly slower (k = 6.7 x 10(2)s(-1)). In basic solution, 1a.(+)-1e.(+) undergo (-)OH-induced deprotonation from the alpha-OH group with k(OH.)approximately equal to 1.4 x 10(10)M(-1)s(-1), leading to a ketyl radical anion, which is oxidized in the reaction medium to the corresponding benzophenone.
“…The ionization energy of DEA is lowered only to 6.95 32 eV. In contrast, the structure of the DMOT is seriously modified because of the steric hindrance between N(CH 3 ) 2 and ortho CH 3 groups inducing the increase of its ionization energy to 7.40 31 eV.…”
Section: B Modeling (1) Molecular Structures and Nr 2 Inversionmentioning
confidence: 96%
“…As a matter of fact, the structures of the fluorescence excitation spectra of DMA and DEA may be explained by assuming the existence of a unique species, as shown by Wallace and al. 29 The structure of DMA is well-known and may not be significantly modified by methyl substitution, as evidenced by a slight decrease of the ionization energy from 7.12 eV 30 to 6.95 31 and 7.06 31 eV respectively. The ionization energy of DEA is lowered only to 6.95 32 eV.…”
Section: B Modeling (1) Molecular Structures and Nr 2 Inversionmentioning
The existence of isomeric forms of donor−acceptor complexes
formed in the supersonic expansion was
evidenced by their fluorescence, fluorescence excitation, and
hole-burning spectra. For each complex, we
observed two types of isomers: one E-isomer with broad structureless
excitation spectra yielding diffuse,
strongly red-shifted exciplex emission and a number of (one to five)
R-isomers with narrow band excitation
spectra yielding a resonant emission upon the excitation of the lowest
vibrational levels of the excited electronic
state and exciplex emission from higher levels. A detailed
analysis of their excitation spectra (spectral shifts,
vibrational structures, bandwidths) is given. The shape of the
ground-state potential energy surface (depths
and positions of the energy minima, heights of energy barriers, etc.)
was determined by calculations involving
the “exchange perturbation” treatment and simulated annealing
method. The relation between the properties
of observed species and calculated configurations is
discussed.
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