Bond Twisting Mechanism in Linear Quinoid Structure

4 Double-Bond Twisting Mechanism in Linear Quinoid Structure 

4 -substituted stilbenes investigated in [12, 31] were divided into three groups according to the intramolecular stabilization of the excited H state (Section 4.2.1.1) 

Group I Stilbene molecules have the weak donor and acceptor substituents. Their excited singlet H state is relatively weakly stabilized by solvents. 

Group II Stilbene molecules have the strong donor substituent (CH 3)2N in the 4-position of the aromatic ring. They are characterized by a large redshift in both the absorption and the fluorescence spectra of trans-stilbenes. The (CH3)2N group considerably stabilizes the H state compared to that of the first group. 

Group III Stilbene molecules have the strong donor-acceptor pairs of 4,4 -substituents and exhibit very large redshifts, compared to the first and second 

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