Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Photobases

Fig. 3. Decay of the photoacid band at 1486 cm 1 (left panel), the rise of the conjugated photobase band at 1503 cm 1 (centre panel) and acetic acid band at 1720 cm 1 (right panel) as function of acetate concentration. The photoacid and photobase signals are in addition affected by rotational diffusion. Fig. 3. Decay of the photoacid band at 1486 cm 1 (left panel), the rise of the conjugated photobase band at 1503 cm 1 (centre panel) and acetic acid band at 1720 cm 1 (right panel) as function of acetate concentration. The photoacid and photobase signals are in addition affected by rotational diffusion.
Ilford uses nearly exclusively resin-coated true photobase for their wide format and desktop media. The ink-receiving layers (IRL) are based on proprietary technology and are apphed in a multi-layer photo-like cascade or curtain coating process. Ilford developed ink receiving layers which are based on either polymers (e.g., gelatin CMC, PVA) or microporous layers based on sUica or lanthanum doped boehmite, or a combination of both. ... [Pg.81]

Pigmented resin banier Photobase -Kodak Royal paper -Clear resin barrier... [Pg.83]

Over the years the field of photoacids (and photobases) has been reviewed many times . The most extensive list of photoacids appeared, so far, in a 1976 review by Ireland and Wyatt The hydroxyarenes are the most widely used photoacids. In polar solutions they may undergo an excited-state proton-transfer reaction according to the general reaction scheme of equations 2-5. [Pg.492]

This stage may involve some further electronic rearrangement in the photoacid toward the formation of the photobase. [Pg.492]

The charge separation stage, hb ip, may involve considerable electronic rearrangement in the photobase. [Pg.493]

Equation 17 may be viewed as an explicit form of the Forster cycle. It depends on both intramolecular and intermolecular factors which determine the extent of the photoacidity. The first factor is the difference between the excited-state and the ground-state proton affinities of the photobase. This difference will be equal to the difference in the intramolecular stabilization of the proton upon the electronic excitation of the acid, and will depend, in general, on the quantum-mechanical properties of the first excited electronic state of the photoacid. The second factor is the difference in the solvation energies of the base and the photoacid upon electronic excitation. The magnitude of the solvation-energy terms will depend in general both on the solvent and the solutes and will depend on the nature of the first electronic state of the photoacid and its conjugate base. [Pg.501]

The traditional approach has been to define photoacidity as an intramolecular property of the photoacid . In terms of equation 17, this approach places the main reason for photoacidity in the reduced proton affinity of the molecular anion in the electronic excited state. Alternatively, this means that photoacidity is mainly the result of the reduction in the dissociation energy of the photoacid in the gas phase upon electronic excitation. What is the reason behind this reduced proton affinity of the photobase ... [Pg.501]

In conclusion, it is the opinion of this review that photoacidity manifests itself in both the photoacid and the photobase sides, the reactant side becoming a stronger acid and the product side becoming a weaker base in the excited state. It is still a matter of additional experimental and theoretical studies to establish if general rules may be drawn up concerning the relative importance and generality of these processes. Similarities to ground-state... [Pg.505]

Successful dimerization of the coum irin derivatives (119) in the solid state has been reported. The photobasicity of several coumarin derivatives (120) has been... [Pg.190]

Figure 9. Scanning Electron Micrograph of polyvinyl alcohol coated barytes photobase paper with and without ink. Figure 9. Scanning Electron Micrograph of polyvinyl alcohol coated barytes photobase paper with and without ink.
For many molecules, due to extensive redistribution of electron densities, acid-base property in the excited state differs considerably from that in the ground state [33 For instance, aromatic amines are weakly basic in the ground state. But many of them become acidic in the excited state and readily donate a proton to a proton acceptor to produce the anion in the excited state. Such a molecule, which behaves as an acid in the excited state, is called a photoacid similarly, photobases are those that display basic properties in the excited state. In many cases, excited state proton transfer (ESPT) results in dual emission bands. One of these emission bands arises om the neutral excited state and bears mirror image relation with the absorption spectrum. The other emission band is due to the excited deprotonated (anion) or protonated species and exhibits a large Stokes shift. [Pg.291]


See other pages where Photobases is mentioned: [Pg.102]    [Pg.190]    [Pg.191]    [Pg.201]    [Pg.414]    [Pg.362]    [Pg.495]    [Pg.495]    [Pg.497]    [Pg.502]    [Pg.502]    [Pg.503]    [Pg.505]    [Pg.506]    [Pg.508]    [Pg.515]    [Pg.515]    [Pg.1500]    [Pg.157]    [Pg.538]    [Pg.212]    [Pg.292]    [Pg.210]    [Pg.211]    [Pg.215]    [Pg.377]    [Pg.378]    [Pg.378]    [Pg.378]    [Pg.378]    [Pg.379]    [Pg.379]    [Pg.379]    [Pg.383]    [Pg.383]    [Pg.384]   
See also in sourсe #XX -- [ Pg.415 ]




SEARCH



Photoacids and Photobases

Photobase

Photobase

© 2024 chempedia.info