Non-linear optical properties of thienylmethylene anilines and benzylidene aminothiophenes

The structures of a series of donor acceptor thienylmethylene anilines (9, 10), benzylidene aminothiophenes (11, 12), and extended structures containing the azobenzene chromophore (16, 17) have been calculated and their hyperpolarizabilities have been assessed using a sum-over-states approach. The results show that low lying excited states involving the thiophene ring exert a pronounced effect on the hyperpolarizability of these systems with N-[(5-nitrothien-2-yl)methylene]-4′-N,N-diethylaminoaniline (9) showing a value which is four times larger than N-[(5-(N-piperidyl)thien-2-yl)methylene]-4′-nitroaniline (10) and about 50% larger than 4-N,N-dimethylamino-4′-nitroazobenzene (8). Extended systems such as (16) or (17) show no advantage over the simpler thiophene (9). Both the thienylmethylene anilines (9, 10) and the extended structure (16) have been synthesised in reasonable yield and high purity by condensing the appropriate arylamine with a thiophene-2-carbaldehyde.