The synthesis and spectral characterization of red dyes containing biphenyl or fluorene conjugation and dicyanovinyl acceptors

Novel dipolar compounds containing diarylamine donors, dicyanovinyl acceptors and either a fluorene or biphenyl linker were prepared in an attempt to unravel the similarities and differences between the biphenyl and fluorene segments in donor-acceptor architectures. The linker segments significantly modify λ_max and the redox potential of the dyes is influenced by the nature of both the amine and linker. Density functional theory calculations performed at the 6-31G(d,p) level revealed that the higher wavelength absorption contains a major contribution from the charge-transfer transition between the amine donor to the dicyanovinyl acceptor. The HOMO is mainly located on the triarylamine segment while the LUMO is spread over the dicyanovinyl. The fluorene based dyes exhibit lower thermal stability than their biphenyl analogues.