Programmable Anisotropic in Diazapyrene Cocrystals With Birefringence Exceeding 1.2.

Area of Science:

• Materials Science
• Optics
• Crystallography

Background:

• Birefringent crystals are crucial for polarization control in nonlinear optics.
• Existing inorganic birefringent crystals face limitations due to metal abundance and sustainability.
• Organic cocrystals present an alternative with tunable properties and simpler preparation.

Purpose of the Study:

• To design and synthesize novel organic cocrystals with high birefringence (Δn).
• To explore the relationship between crystal packing anisotropy and birefringence.
• To investigate the potential for metal-free, tunable optical materials.

Main Methods:

• Design of diazapyrene derivatives and formation of cocrystals with benzene derivatives.
• Measurement of birefringence (Δn) across a series of 13 crystals.
• Analysis of crystal packing using a geometric descriptor (ΔS) and correlation with Δn.

Main Results:

• Synthesized 13 crystals (3 single-component, 10 cocrystals) with tunable Δn ranging from 0.152 to 1.269.
• Identified two compositions (D27N, D13N) with exceptional birefringence (Δn = 1.223, 1.269), exceeding inorganic counterparts.
• Established a Boltzmann-type relationship linking crystal packing anisotropy (ΔS) to macroscopic Δn.
• Demonstrated modulation of nonlinear optical responses, including second-harmonic generation.

Conclusions:

• Organic cocrystals offer a metal-free, designable route to high-Δn optical materials.
• The study provides a predictive metric (ΔS) for discovering new anisotropic optical crystals.
• This work advances the development of sustainable and high-performance optical materials.