Crystal, molecular and electronic structure of N,N'-diphenyl-N,N'-bis(2,4-dimethylphenyl)-(1,1'-biphenyl)-4,4'-diamine and the corresponding radical cation

Oxidation of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD, 1a) and N,N'-diphenyl-N,N'-bis(2,4-dimethylphenyl)- (1,1'-biphenyl)-4,4'-diamine (1b) with SbCl5 affords the corresponding radical cations quantitatively. The crystal and molecular structure of 1b and [1b]SbCl6, the first tetraphenyl benzidene derivatives to be characterised crystallographically in both the neutral and radical cation states, reveal molecular parameters in agreement with the predictions made on the basis of DFT studies. Analysis of the NIR transition in the radical cations [1](+.) allows an estimate of the electronic coupling parameter V (1a(+.) 3200 cm(-1); 1b(+.) 3300 cm(-1)), the reorganisation energy lambda(1a(+.) 7500 cm(-1); 1b(+.) 7800 cm(-1)), and the linear coupling constant I (1a(+.) 3100 cm(-1); 1b(+.) 2700 cm(-1)) of the symmetric mode.