Synthesis of Phenylbutadiynylpyridinium Derivatives for Nonlinear Optics

Abstract

1-Methyl-4-{[4-(dimethylamino)phenyl]butadiynyl}pyridinium (PBP) derivatives with iodide or benzenesulfonate anion were synthesized as potential compounds for both second- and third-order NLO applications. PBP shows peculiar absorption spectrum in methanol, in which molar extinction coefficient at absorption maximum (λ_max) decrease irrespective of bathochromic shift of λ_max compared with the corresponding compound with one triple bond between two aromatic rings. From semiempirical MO calculations, it was explained by aromatic-ring rotation of PBP in methanol. Activity on second-harmonic generation (SHG) was found in four out of thirteen compounds synthesized. Although most of PBP derivatives were found to show exothermic reaction before melting, pure solid-state polymerization was not confirmed in these compounds.

Keywords:

• DAST
• ionic dye
• nonlinear optics
• organic crystal
• solid-state polymerization

Acknowledgments

This work was supported by Tokyo Ohka Foundation for the Promotion of Science and Technology and Grant-in-Aid for Scientific Research on Priority Areas (No. 446, Super-hierarchical Structures) from the Ministry of Education, Culture, Sports, Science and Technology.

Notes

^a Peak temperature measured by DTA.

^b1H- and ¹³C-NMR spectra were measured in CDCl₃ for 5 and 6 and in CD₃OD for 7a. In ¹³C-NMR data of 7a, a peak assigned to methyl carbon attached to the pyridinium ring was not clearly detected because of overlap with split peaks of deuterated-methanol carbon.

^cExothermic peak due to thermal polymerization.

^a Onset of an exothermic peak.

^b Onset of an endothermic peak followed by an exothermic peak.

^c G: Green emission due to SHG, R: Red emission due to multiphoton fluorescence.