A Polar Titanium-Organic Chain with a Very Large Second-Harmonic-Generation Response

Area of Science:

• Materials Science
• Inorganic Chemistry
• Crystallography

Background:

• Noncentrosymmetric (NCS) materials are crucial for nonlinear optics.
• Titanium-organic compounds offer tunable properties for advanced applications.
• Understanding structure-property relationships in NCS materials is key for developing new optical devices.

Purpose of the Study:

• To synthesize and characterize a novel NCS titanium-organic compound.
• To investigate the structural features responsible for its properties.
• To evaluate its potential for nonlinear optical applications and explore its dynamic behavior.

Main Methods:

• Solvothermal synthesis of the titanium-organic compound CAUMOF-18.
• Structural analysis using X-ray diffraction to determine the polar chain arrangement.
• Second-harmonic-generation (SHG) measurements to quantify nonlinear optical efficiency.
• Investigation of water-molecule-induced transformations.

Main Results:

• Successful synthesis of [H2N(CH3)2]TiO{[NC5H3(CO2)2][NC5H4(CO2)]} (CAUMOF-18) with a unique NCS polar chain structure.
• CAUMOF-18 exhibits a strong type I phase-matchable SHG efficiency, 400 times that of α-SiO2.
• The material undergoes reversible centricity conversion and topotactic transformation to TiO2 microrods in the presence of water molecules.

Conclusions:

• CAUMOF-18 is a promising NCS material for nonlinear optics due to its high SHG efficiency.
• Hydrogen bonding and π-π interactions play a critical role in stabilizing its polar structure.
• The observed water-molecule-driven transformations offer pathways for responsive materials and novel TiO2 nanostructures.