Twisted intramolecular charge transfer compound

S. Tazuke, R. K. Guo, and T. Ikeda, Time-resolved fluoresence spectroscopy of a twisted intramolecular charge transfer compound bonded to polymers, /. Phys. Chem. 94, 1408(1990). 

RD Schulte, JF Kauffman. Fluorescence from the twisted intramolecular charge transfer compound bis(4,4 -dimethylaminophenyl)sulfone in ethanol/C02 a probe of local solvent composition. Appl Spectrosc 49 31, 1995. 

K. A. Al-Hassan and T. Azumi, The role of free volume in the twisted intramolecular charge transfer (TICT) emission of dimethylaminobenzonitrile and related compounds in rigid polymer matrices. Chem. Phys. Lett. 146, 121 (1988). 

V,/V-Dimethylamino)benzonitrile (DMABN) and its derivatives, as a class of organic donor-acceptor compounds, exhibit dual fluorescence, one related to the local excited state ( B band) and the other ascribed to the twisted intramolecular charge transfer (TICT) state ( A band).17 As expected, compound 818 exhibits dual fluorescence, showing two fluorescence bands centered at 350 and 432 nm, which can be ascribed to the corresponding band (from the local excited state) and A band (from the TICT state), respectively. After oxidation of TTF unit in 8, the fluorescence intensity of A band decreases while that of band increases slightly. As expected, further reduction of TTF" + into neutral TTF unit leads to the restoration of the fluorescence spectrum of 8. Therefore, the dual fluorescence spectrum of 8 can be reversibly modulated by redox reactions of TTF unit in 8. 

Compounds 268a and 269a showed large Stokes shifts in polar solvents. Such large Stokes shifts have been observed in many TICT (twisted intramolecular charge transfer) molecules. Fluorescence decay time measurement indicated that there were two kinds of excited states, fast and slower decaying components, and the latter was the emission from the more polar state. 

The discovery of the dual fluorescence of the simple donor-acceptor substituted benzene derivative 4JV,iV-dimethylaminobenzonitrile (DMABN) by Lippert et al. [1] and the subsequent model compound studies by Grabowski et al. [2-6] including rigidized and pretwisted compounds such as MIN, TMABN and CBQ gave birth to the idea of Twisted Intramolecular Charge Transfer (TICT) states. 

The Twisted Intramolecular Charge Transfer (TICT) model was put forward by Grabowski and coworkers [2,3,15] to account for the observation that the dual fluorescence of DMABN with its normal band (B band) at around 350 nm and its anomalous one (A band, around 450 nm in medium polar solvents) depends on the conformational freedom of the dimethylamino (DMA) group For compounds like MIN, where the DMA group is more or less fixed to a coplanar conformation with the benzonitrile sceleton, and where the lone pair orbital on the amino nitrogen is nearly parallel to the carbon p-orbitals constituting the benzonitrile 7t-system, only the B band is observed. For the... 

As a second example we consider, briefly, twisted intramolecular charge transfer in aminobenzonitrile compounds.This is a donor-acceptor system (Figure 3.30). The S2 excited state of this system is a charge-transfer state involving the transfer of an electron from the nitrogen atom to the benzene ring. The Si excited state is a locally excited state, involving the excitation of... 

In addition to these photophysical processes, twisted intramolecular charge transfer (TICT) process (non-radiative process) also takes place to return to ground state. Molecules of compounds such as dimethyiaminobenzonitrile (DMABN) are flexible. These are planar in the ground state, but are twisted in excited state. The twisted conformation is able to transfer its full electronic charge from one part to another in polar solvents and thus deactivated to ground state (Fig. 6.5) [4]. 

Earlier investigations have shown that in certain derivatives, such as ammosaHcylates and salicylide-neanilines, a twisted intramolecular charge transfer (TICT) state is formed and is followed by the ESIPT. These compounds show multiple fluorescence. 

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