Bichromophoric system

J. Kroon, A. M. Oliver, M. N. Paddon-Row, J. W. Verhoeven, Observation of a Remarkable Dependence of the Rate of Singlet-Singlet Energy Transfer on the Configuration of the Hydrocarbon Bridge in Bichromophoric Systems , J. Am Chem Soc 1990,112, 4868-4873. 

Some bichromophoric systems, whose structure is based on the donor-bridge-acceptor principle, can undergo complete charge transfer, i.e. electron transfer. The resulting huge dipole moment in the excited state explains the very high sensitivity to solvent polarity of such molecules. An example is FP (l-phenyl-4-[(4-cyano-l- ... 

The most frequently used acyl derivatives, i.e., benzoates and cinnamates substituted in the 4-position, are listed in Table 7. The analysis of the stereochemistry of the bichromophoric system including a benzoate (cinnamate) chromophore is greatly simplified by its preference for s-trans conformation at the C(0)-0 bond, in which the carbonyl group is staggered ca. 30° to either side of the carbinyl C H bond. Consequently the direction of the electric dipole moment of the charge-transfer transition is approximately parallel to the C(H)-Q bond (Figure 16). 

Perylene-linked systems represent another class of useful compounds for PET studies. Classic cases are 21 and 22. They represent a family of closely related bichromophoric systems with properties designed to utilize PET strategies . 

Bichromophoric Systems, Excited State Behavior of Some (De Schryver, Boens and Put) 10 359... 

In bichromophoric systems, fccR values computed from the cationic decays are found to be similar to those obtained from the analysis on the decay of the anionic species. 

C. Curutchet and B. Mennucci, Toward a molecular scale interpretation of excitation energy transfer in solvated bichromophoric systems, J. Am. Chem. Soc., 127 (2005) 16733-16744. 

Gilbert s group report some new results for the inter- and intramolecular addition of polarised alkenes to naphthalenes. It is found that the bichromophoric system (113) undergoes intramolecular addition to give (114) while... 

Using rigid bichromophoric systems with donor and acceptor components ster-ically fixed by spacers, the dependence of electron transfer on the geometry as well as on solvation has been studied. According to Figure 5.40 exciplex fluorescence to be expected from the diagram in Figure 5.39 can be observed for system 22a in polar solvents, whereas electron transfer does not occur in solvents of low polarity, and only fluorescence of the donor component is seen. 

Excited State Behavior of Some Bichromophoric Systems... 

Table 1, part 1 lists the bichromophoric systems in which exclmer fluorescence has been observed until now the frequency of the maximum and the quantum yield of fluorescence (if reported) are given. 

TABLE 1. Bichromophoric Systems Showing Emission from Intramolecular Excited Complexes. 

As both the excitation resonance and charge transfer should be weaker in the triplet state than in the singlet, the binding energy in triplet excimers is appreciably smaller. As the entropy loss is supposed to be smaller in Intramolecular exclmer formation, triplet excimers are more likely to be observed in bichromophoric systems than in monofunctional ones (9). A further difficulty that arises is that the study of phosphorescence in liquid solutions is very difficult. Molecules with a ground state... 

Intramolecular excited state complex formation can be an important deactivation process in bichromophoric systems. The governing factors are the lifetime of the excited state involved and the free energy change accompanying the reaction. Three possibilities exist ... 

If there is a difference in the respective energy levels of the excited states of both chromophores in a bichromophoric system, excitation transfer can occur from one chromophore to the other. This energy transfer can occur as well before as after Intersystem crossing of the originally excited chromophore. The systems studied are divided into two main classes, according to the method used in the detection. The excitation transfer can be monitored either by spectroscopic methods or by reaction of the acceptor chromophore. 

Flexible Bichromophoric Systems. Chemical changes in the acceptor moiety have been used as detection method for excitation transfer of the blchromophorlc systems with a flexible link mentioned in Table 2. 

If the bichromophoric system is suitably chosen to eliminate intramolecular processes and to ensure the possibility of inter-molecular reaction, a polymer can be formed. Where previously the term photopolymerization was used to Indicate photoinltiated chain processes (161), the present discussion of nonconjugated blchromophores is from a different point of view. The term "photopolymerization" as defined here, is a polymerization process in which every chain-propagating step Involves the absorption of a photon (162,163). This definition Implies that photopolymerization is a stepwise reaction, in contrast to photoinltiated polymerization, which Is a chain process. A sensitized photopolymerization is a photopol ymerlzation in which the reacting... 

This reaction could be extended to bichromophoric systems, resulting in the formation of polymers with oxetane rings in the main chain. 

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