Elastic organic crystals are the materials foundation of future lightweight flexible electronic, optical and sensing devices, yet precise control over their deformation has not been accomplished. Here, we report a general non-destructive approach to remote bending of organic crystals. Flexible organic crystals are coupled to magnetic nanoparticles to prepare hybrid actuating elements whose shape can be arbitrarily and precisely controlled simply by using magnetic field. The crystals are mechanically and chemically robust, and can be flexed precisely to a predetermined curvature with complete retention of their macroscopic integrity at least several thousand times in contactless mode, in air or in a liquid medium. These crystals are used as optical waveguides whose light output can be precisely and remotely controlled by using a permanent magnet. This approach expands the range of applications of flexible organic crystals beyond the known limitations with other methods for control of their shape, and opens prospects for their direct implementation in flexible devices such as sensors, emitters, and other (opto)electronics. 

/pdf/remote-and-precise-control-over-morphology-and-motion-of-3d42qmax.pdf

Remote and precise control over morphology and motion of organic crystals by using magnetic field

Operation of temperature sensors over extended temperature ranges, and particularly in extreme conditions, poses challenges with both the mechanical integrity of the sensing material and the operational range of the sensor. With an emissive bendable organic crystalline material, here we propose that organic crystals can be used as mechanically robust and compliant fluorescence-based thermal sensors with wide range of temperature coverage and complete retention of mechanical elasticity. The exemplary material described remains elastically bendable and shows highly linear correlation with the emission wavelength and intensity between 77 K to 277 K, while it also transduces its own fluorescence in active waveguiding mode. This universal new approach expands the materials available for optical thermal sensing to a vast number of organic crystals as a new class of engineering materials and opens opportunities for the design of lightweight, organic fluorescence-based thermal sensors that can operate under extreme temperature conditions such as are the ones that will be encountered in future space exploration missions. 

/pdf/fluorescence-based-thermal-sensing-with-elastic-organic-1sjczbkv.pdf

Fluorescence-based thermal sensing with elastic organic crystals

/pdf/fluorescence-based-thermal-sensing-with-elastic-organic-1746f6vw.pdf

In a recent study, Dey et al.1
propose a mechanism of elastic bending in co-crystals of caffeine,
4-chloro-3-nitrobenzoic acid and methanol (1) in which mechanical interlocking
is proposed to allow for the reversible flexibility observed. We have now determined the mechanism to atomic
resolution using micro-focused synchrotron radiation,2 which is
different to that previously reported. When subjected to strain the
inter-molecular distances change and hydrogen-bonded dimers rotate over two orthogonal
directions to allow the compression and expansion producing flexibility.

The mechanism of bending in co-crystals of caffeine and 4-chloro-3-nitrobenzoic acid.

Although the famous brittle characteristics of molecular crystals are unfavorable when they are used as flexible smart materials (FSMs), an increasing number of organic crystal-based FSMs have been reported recently. This breaks the perception of their stiff and brittle properties and promises a bright future for basic research and practical applications. Crystalline smart materials present considerable advantages over polymer materials under certain circumstances, rendering them potential candidates for certain applications, such as rapidly responsive actuators, ON/OFF switching, and microrobots. In this review, we summarize the recent developments in the field of organic crystal-based FSMs, including the derivatives of azobenzene, diarylethene, anthracene, and olefin. These organic crystal-based FSMs can bend, curl, twist, deform, or respond otherwise to external stimuli, such as heat or light. The detailed mechanisms of their smart behaviors are discussed with their potential applications in exciting intelligent fields. We believe this review could provide guidelines toward future fabrication and developments for novel organic crystal-based FSMs and their advanced smart applications. 

/pdf/organic-crystal-based-flexible-smart-materials-14fusqt3.pdf

Organic crystal-based flexible smart materials

The discovery of molecular single crystals that display interesting elastic behaviour has generated excitement regarding their potential applications as it has upended the common perception of crystals as brittle objects. In order to design new functional materials based on molecular crystals, a comprehensive understanding of how these materials respond to deformation on a molecular-level is required. An introduction to the underlying mechanical theory and how it may be applied to single crystals is provided, along with a comprehensive discussion on how these mechanical properties can be characterised. While this field has already presented a large number of elastically flexible crystals, there is a lack of detailed mechanical characterisation data and some contention regarding the atomic-scale mechanism of elasticity. Due to the discrepancies and contradictions between theories proposed in the literature, it is not yet understood why some crystals are elastic while others shatter under applied force. To dispel ambiguity and guide future research, a set of criteria are proposed to define an elastically flexible crystal, so that these materials may find applications among future technologies.

Analia I. Chamorro Orué

Papers

Elastically flexible molecular crystals.

On the activation of PhICl2 with pyridine