Compounds undergoing photoinduced intramolecular charge transfer ICT and internal rotation

Compounds undergoing photoinduced intramolecular charge transfer (ICT) and internal rotation 

Such a solvent relaxation explains the increase in the red-shift of the fluorescence spectrum as the polarity of the solvent increases. The effect of polarity on fluorescence emission will be further discussed in Chapter 7, together with polarity probes. Moreover, when a cation receptor is linked to an intramolecular charge transfer fluorophore so that the bound cation can interact with either the donor group or the acceptor group, the ICT is perturbed the consequent changes in photophysical properties of the fluorophore can be used for sensing cations (see Section 10.3.3). 

Relaxation towards an ICT state may be accompanied by internal rotation within the fluorophore. The prime example of great interest is 4-N,N-dimethylamino-benzonitrile (DMABN). 

The twisting assumption can be demonstrated by comparing the fluorescence characteristics of the bridged model compounds 2 and 3 with those of DMABN (1) in a polar solvent no twist is possible in compound 2 and LE fluorescence is solely 

Internal rotation, accompanying solvent relaxation or not, can occur in many fluorophores, but dual fluorescence and right angle twist (required for full charge 

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