Systematic Investigations on 1,2,3-Triazole-Based Compounds Capable of Second Harmonic Generation

1,2,3-Triazole-functionalized
ene–yne compounds, synthesized
by thiophene (selenophene) ring fragmentation followed by azide–alkyne
cycloaddition, were investigated as a basis for nonlinear optical
(NLO) materials capable of second harmonic generation (SHG). The structure–property
relationship was mapped by systematic variation of the molecular scaffold,
viz., elongation of the alkyl groups, isomerizations of both the double
bond as well as the triazole moiety, sulfur oxidations, and a sulfur–selenium
exchange. Nine novel molecular compounds were synthesized, of which
eight are solids at room temperature. The latter were characterized
by single-crystal X-ray diffraction (XRD). Five crystal structures
lacked of inversion symmetry, a prerequisite for NLO activity. The
corresponding materials were examined regarding SHG, UV–vis
absorption, and powder XRD. By substituting S for Se, we were able
to increase the SH intensity by a factor of 20. On the basis of the
results, we propose a strategy to further improve the SHG efficiency
of this class of materials.