Extended conjugation in di- and tri-arylmethanes. Part II. Electronic absorption spectra of longitudinally conjugated naphthalene analogues of Crystal Violet, Malachite Green, and Michler's Hydrol Blue

Abstract

Spectral studies show that terminal nitrogen atoms attached to longitudinally conjugated naphthalene groups in analogues of Crystal Violet, Malachite Green, and Michler's Hydrol Blue have a greater tendency to conjugate with the central carbon atom than those in the corresponding 9.9-dimethylfluorene analogues. Conjugation is most effective in the Crystal Violet analogue (I1 ; R = NMe,) in which a high resonance-energy counterbalances the high energy of the quinonoid naphthalene group. 6

The effects of cyclic terminal groups in di- and tri-arylmethane dyes. Part 2.1 Steric and electronic effects in derivatives of Victoria Blue

“…However, terminal nitrogen atoms attached to longitudinally conjugated naphthalene moieties (2,6-linked) conjugate to a greater extent 15 and lead to a red shift and an increase in intensity of the y-band. In the case of the transversely conjugated naphthalene derivatives (1,4-linked), electronic effects are dominated by steric features.…”

“…3 through more than one benzene ring, 12 notably in the biphenyl 13 and fluorene 14 analogues of CV, but in both cases the transmission of mesomeric effects is considerably reduced. However, terminal nitrogen atoms attached to longitudinally conjugated naphthalene moieties (2,6-linked) conjugate to a greater extent 15 and lead to a red shift and an increase in intensity of the y-band. In the case of the transversely conjugated naphthalene derivatives (1,4-linked), electronic effects are dominated by steric features.…”

Extended conjugation in di- and tri-arylmethane dyes. Part 4. Steric and electronic effects in analogues of Malachite Green containing a 2H-1-benzopyran unit

“…The 2-naphthyl derivative of MG exhibits increases in λ max and ε max of both bands similar to those of the 7-chromenyl dye and of the y-band of the 6-isomer. 15 The 4-and 8-chromenyl dyes 25d,c are analogous to the transversely conjugated 1-naphthyl derivative of MG 16 in which both steric and electronic factors are important and the spectral parameters of these systems are quite similar. The x-bands show a shift to longer wavelength and an increase in intensity, together with blue shifts and reduction in intensity of the y-bands.…”

“…Introduction of biphenyl 13 and fluorene 14 moieties in place of the phenyl ring has only a minimal effect on the visible spectra and suggests that conjugation through the extended chromophoric system is ineffective even when twisting about the interannular bond is curtailed as in the fluorene analogue. The 2-naphthyl derivative of Malachite Green 2 15 exhibits a red shift of the y-band which implies enhanced conjugation attributable to the extension of the chromophore along the y-axis, since there is no additional steric hindrance associated with a longitudinally bonded naphthalene unit. However, a comparison between MG and its 1-naphthyl derivative 3 shows red shifts of both the x-and y-bands, but the response in ε max of the two bands is different.…”