Extended conjugation in di- and tri-arylmethanes. Part III. Electronic absorption spectra of transversely conjugated naphthalene analogues of Crystal Violet, Malachite Green, and Michler's hydrol blue

Abstract

Spectral changes caused by the effect of the additional ring in transversely conjugated naphthalene analogues of Crystal Violet, Malachite Green, and Michler's Hydrol Blue are described and discussed. Although peri-hindrance of the terminal dimethylamino-groups leads to incomplete conversion of dye base into dye in acid solution, and to ready protonation of the crowded groups, the univalent cations are shown to be electronically symmetrical and pronounced bathochromic shifts of the first bands are observed. The carbonyl group of bis-(4-dimethylamino-lnaphthyl) ketone is unusually resistant to reduction.

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

“…In the case of the transversely conjugated naphthalene derivatives (1,4-linked), electronic effects are dominated by steric features. 16 Thus, the spectral response is a red shift and increase in ε max of the x-band, whilst the y-band is red shifted but reduced in intensity, behaviour indicative of enforced rotation about the y-axis caused by crowding about the central carbon atom. There has been much interest in compounds based on this last system and Victoria Blue (VB) derivatives 2 (R 1 = R 2 = NMe 2 ) were first patented in the late nineteenth century because of their value for colouring paper, silk and wool in bright shades of blue and purple-red.…”

Synthesis and electronic absorption spectra of some novel methoxy half-analogs of Malachite Green and Brilliant Green

“…This type of by-product formation did not take place in the case of 2-and 3-bromoanisoles [12]. It is possible to minimize such interfering side reactions by using the more reactive complex formed between butyl lithium and bis-1,2-dimethylaminoethane [9] and also employing shorter reaction periods. By using this complex, it is possible to obtain good yields of any methoxyphenyl lithium derivatives.…”

“…To a stirred ethereal solution of butyl lithium, redistilled 1,2-bisdimethylamino ethane (2.0 g) was added dropwise over 15 min and the stirring was continued for 30 min. To the solution of butyl lithium-1,2-bismethylaminoethane complex [9], an ethereal solution of redistilled bromo derivatives such as 4-bromoanisole, 3-bromobenzotrifluride, and etc (0.02 M in 20 ml ether) was introduced and stirring was continued for 30 min before further reaction. The resultant ethereal solution was reacted with appropriate ketone (0.01 M) in dry THF (80 ml).…”

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.…”

“…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. 16 The x-band becomes more intense whereas the y-band decreases in intensity, behaviour which is characteristic of enforced rotation about the y-axis caused by crowding at the central carbon atom. Steric and electronic factors are in opposition in the transversely conjugated naphthalene dye and the unexpected red shift of the y-band reflects the electronic contribution of the 1-naphthyl group.…”