Triphenylamine Triphenylmethane

Steric hindrance between phenyl substituents can effectively reduce conjugation. This is most pronounced for triphenylcarbenium ions - like the well-known triphenylmethane dyes (cf. [115]) - and triphenylamine derivatives (cf. [113]). Bridging of phenyl substituents of course alleviates this... 

Larger ir systems based on the sterically encumbered oligophenyl type give as disappointing results as in the ID series, as shown by a series [113] of triphenylamine and pyrimidine derivatives (Stadler et al., 1995, 1996c). The same holds true for simple triphenylmethane dyes, as demonstrated by extensive investigations on crystal violet [115] (Kaatz and Shelton, 1996 Morrison et al., 1996 Noordman and van Hulst, 1996) which showed that... 

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