
%0 Journal Article
%A Ashwell, Geoffrey J. 
%A Williamson, Patricia C. 
%A Green, Andrew 
%A Bahra, Gurmit S. 
%A Brown, Christopher R. 
%T Aggregation-Induced Linear and Non-Linear Optical Properties of Four Hydroxy-Substituted Analogues of 2,4-Bis[4-(dibutylamino)phenyl]squaraine
%J Australian Journal of Chemistry
%D 1998/07/13
%V 51
%N 7
%P 599-604
%K 
%R https://doi.org/10.1071/C98059
%U https://www.publish.csiro.au/paper/C98059 
%X Langmuir films of the title compound, 2,4-bis&#91;4-(dibutylamino)phenyl&#93;squaraine, Sq0, and its substituted analogues, Sq1 (monohydroxy) to Sq4 (tetrahydroxy), exhibit three well defined phases at the air&#8211;water interface: &lgr;max 525&#8211;550 nm (H-aggregate); 660&#8211;670 nm (intermediate); 760&#8211;770 nm (J-aggregate). The monolayer spectra are influenced by the surface pressure and the number of hydroxy substituents and, when the monolayers are transferred to a solid substrate, there is a correlation between the linear and non-linear optical behaviour of the Langmuir-Blodgett films. Second-harmonic generation has been observed even though the unit molecular structures of two analogues, Sq0 and Sq4, are centric. The behaviour is aggregation-induced and there is evidence that the dyes associate in dilute solution. The electrospray ionization mass spectra exhibit peaks with high mass/charge (m/z) ratios; the data conform to the dimeric aggregate and, for solutions of two or more squaraines, corroborate the existence of heteromolecular associates. 
