Intramolecular Charge Transfer ICT

Fig. 1 Mesomeric structures of a para-substituted benzene intramolecular charge transfer (ICT) complex in the ground state and in the dipolar excited state...

Interestingly, the vast majority of luminescent molecules that fulfil the latter condition are those displaying an intramolecular charge transfer (ICT)... 

Figure 1. Some examples of luminescent probes with intramolecular charge transfer (ICT) electronic excited states. The numbers in parenthesis indicate the typical wavelengths of the excitation/emission maximums for each of them in polar media however, introduction of chemical groups in the unsubstituted molecular frame or attachment to a solid support may shift those values.

The optical properties of organic dyes (Fig. ld-f, Table 1) are controlled by the nature of the electronic transition(s) involved [4], The emission occurs either from an electronic state delocalized over the whole chromophore (the corresponding fluorophores are termed here as resonant or mesomeric dyes) or from a charge transfer (CT) state formed via intramolecular charge transfer (ICT) from the initially excited electronic state (the corresponding fluorophores are referred to as CT dyes) [4], Bioanalytically relevant fluorophores like fluoresceins, rhodamines, most 4,4 -difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPY dyes), and cyanines (symmetric... 

In the excited state, the redistribution of electrons can lead to localized states with distinct fluorescence spectra that are known as intramolecular charge transfer (ICT) states. This process is dynamic and coupled with dielectric relaxations in the environment [16]. This and other solvent-controlled adiabatic excited-state reactions are discussed in [17], As shown in Fig. 1, the locally excited (LE) state is populated initially upon excitation, and the ICT state appears with time in a process coupled with the reorientation of surrounding dipoles. 

Donor-acceptor 7i-conjuga ted (D-rc-A) compounds have led to numerous theoretical and experimental studies to explore the origin of intramolecular charge-transfer (ICT) fluorescence. This property can be used in order to have low bandgap materials. 

Red-shifted luminescence is also common to molecules that sustain intramolecular charge transfer (ICT) excited states. As shown in Fig. 9, an electron-hole... 

Figure 9 Intramolecular charge transfer (ICT) emission evolves from a localized excited state (LE). If a metal ion-binding site is present (indicated by the half-circle), ICT emission may be stabilized or destabilized depending on whether the metal ion ( ) binds is at the electronegative or electropositive end of the Jt-aromatic system.

Para-nitroaniline (PNA) represents one of the simplest compounds low lying excited states characterized by an with intramolecular charge transfer (ICT) from -NH2 to -N02, thus extremely sensitive to the presence of a stabilizing polar solvent, and therefore serves as an important model for theoretical [30-32] and experimental [33-38] studies. 

Table 7-3. DFT/TDDFTand experimental dipole moments p. (in Debye) of the ground state (GS) and of the Franck-Condon intramolecular charge transfer (ICT) stateof pNA in gas phase and in solution...

In the present section, we first describe the details of the intramolecular charge-transfer (ICT) state formation in several directly connected (i.e., = 0) EDA molecules from our recent studies, and then review the reported features of the bridged EDA molecules. 

In the last part of this chapter, intramolecular charge transfer (ICT) in anthryl derivatives with linked donor-acceptor parts was discussed. Ultrafast spectroscopy has been applied both for structural characterization and for real-time probing of the ICT in this case. Microscopic solvation effects on the torsional motions and the ICT in the molecules have been examined by the use of their clusters with polar solvents. One of the most important problems which awaits for further studies is an ambiguous description of the electronic character of the charge-separated states in the systems. So far, high-level quantum-mechanical calculations have not been able to deal with such large molecular systems, but reliable evaluation of electronically... 

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