V-Shaped Methylpyrimidinium Chromophores for Nonlinear Optics

Area of Science:

• Organic Chemistry
• Materials Science
• Nonlinear Optics

Background:

• Development of organic chromophores with significant nonlinear optical (NLO) properties is crucial for advanced photonic applications.
• Pyrimidinium salts offer a versatile scaffold for designing molecules with tailored electronic and optical characteristics.

Purpose of the Study:

• To design and synthesize novel V-shaped methylpyrimidinium salts incorporating diphenylamino electron-donating groups.
• To investigate the linear and nonlinear optical properties of these novel chromophores.
• To evaluate the influence of substitution patterns on the NLO response.

Main Methods:

• Regioselective N(1) monomethylation of pyrimidine derivatives using methyl methanesulfonate.
• Experimental study of linear optical properties.
• Theoretical calculations using (Time-Dependent) Density Functional Theory ((TD)-DFT).
• Measurement of second-order nonlinear optical (NLO) properties via electric field induced second harmonic generation (EFISH) in chloroform.

Main Results:

• Four V-shaped methylpyrimidinium salts were successfully synthesized.
• All synthesized salts exhibited promising NLO properties with molecular hyperpolarizability (μβ₀) values greater than 1000×10⁻⁴⁸ esu.
• The 2,4-disubstituted pyrimidinium core demonstrated a superior NLO response and dipole moment compared to the 4,6-disubstituted core.
• (E,E)-2,4-Bis[4-(diphenylamino)styryl]-1-methylpyrimidin-1-ium methanesulfonate showed the highest NLO response (μβ₀ =2500×10⁻⁴⁸ esu) and a figure of merit of 3.4×10⁻⁴⁸ esu·(mol·g⁻¹).

Conclusions:

• The study successfully designed and characterized novel methylpyrimidinium salts with significant NLO properties.
• The 2,4-disubstitution pattern on the pyrimidinium core is advantageous for enhancing NLO performance.
• The lead compound presents a promising candidate for applications requiring efficient second-order nonlinear optical materials.