Fluorescent PCT photoinduced charge transfer cation sensors

Fluorescent PCT (photoinduced charge transfer) cation sensors 10.3.3.1 Principles 

2 PCTsensors in which the bound cation interacts with an electron-donating group 

This interpretation is supported by a thorough study of the photophysics of PCT-1 and its complexes with Li+ and Ca2+ (Martin et al., 1994). In particular, subpicosecond pump-probe spectroscopy provided compelling evidence for the disruption of the link between the crown nitrogen atom and the cation. A photo- 

Such a photodisruption results in a lower stability of the complexes in the excited state. Therefore, excitation of these complexes by an intense pulse of light is expected to cause some cations to leave the crown and diffuse away, provided that the time constant for total release of the cation from the crown is shorter than the lifetime r of the excited state (for a discussion on this point, see Valeur et al., 1997). 

Intramolecular charge transfer in conjugated donor-acceptor molecules may be accompanied by internal rotation leading to TICT (twisted intramolecular charge transfer) states. A dual fluorescence may be observed as in PCT-5 (Letard et al., 1994) (which resembles the well-known DMABN (see section 3.4.4) containing a dimethylamino group instead of the monoaza-15-crown-5) the short-wavelength 

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