Crystal-based optical devices typically use inelastic crystals. Devices such as optical waveguides, cavities, lasers, circuits, and field‐effect transistors are all generally based on rigid platforms. Next-generation smart technologies require flexible photonic circuits, based on flexible crystals with dynamic mechanical and photonic properties. However, it is challenging to fabricate and manipulate such crystals and to correlate their molecular packing and intermolecular interactions with their properties.
Sanjio Zade, C. Malla Reddy, Indian Institute of Science Education and Research, Kolkata, Rajadurai Chandrasekar, University of Hyderabad, India, and colleagues have developed flexible optical waveguiding crystals that can generate and transduce light signals of different wavelengths—a characteristic called wavelength division multiplexing (WDM). The team prepared millimeter-long, mechanically flexible, fluorescent dithieno[3,2-a:2′,3′-c]phenazine crystals (compound pictured above). Combined laser confocal and atomic force microscopy (AFM) techniques were used to visualize and bend the microcrystals.
The crystal has a herringbone-like structure with dominant π‐stacking interactions along the long axis. In this structure, the rotation of molecules can facilitate compression or elongation, depending on the direction (pictured below). This could explain the high flexibility. The flexible crystal waveguides can be used to switch output signal colors for WDM technologies by varying the optical path lengths of the transducing light. The researchers also used the crystals to create a microcircuit by coupling two arc-shaped waveguides (pictured below). The circuit can split an optical signal input and deliver it to two output terminals.
- Mechanophotonics: Flexible Single-Crystal Organic Waveguides and Circuits,
Mari Annadhasan, Abhijeet R. Agrawal, Surojit Bhunia, Vuppu Vinay Pradeep, Sanjio S. Zade, C. Malla Reddy, Rajadurai Chandrasekar,
Angew. Chem. Int. Ed. 2020.