Vibrational spectra of nonlinear optical chromophores based on octopolar C3-symmetric 1,3,5 trisalkynylbenzenes

The vibrational Raman spectra of two C3-symmetry octopolar compounds constructed with alkynylbenzenes as arms and a benzene moiety as the core have been obtained, calculated theoretically and assigned to vibrational normal modes. The changes in the spectra upon inversion of the substitution pattern have been interpreted with the help of the electronic absorption spectra and theoretical calculations. The mitigation of conformational crowding when the core is substituted with fluorine atoms instead of methyls is the key factor responsible from the differences in the Raman frequencies.