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Introduction to Organic Photo Actuator Materials and Devices
Published in Sam-Shajing Sun, Larry R. Dalton, Introduction to Organic Electronic and Optoelectronic Materials and Devices, 2016
Lingyan Zhu, Taehyung Kim, Rabih O. Al-Kaysi, Christopher J. Bardeen
The details of a molecule’s chemical structure affect both its crystal packing and its photoreactivity in the solid state [65]. For anthracene crystals, the reactive partners need to be within a distance of 4.2 Å for the photocycloaddition reaction to occur [66]. Fortunately, organic chemistry provides many possibilities to modify the molecular structure. For example, 9-tert-butylanthroate (9TBAE) crystals can exhibit large expansions upon irradiation, but this photochemistry is irreversible. Simply removing the tert-butyl group from 9TBAE yields 9-anthracene carboxylic acid (9AC) [67], which crystallizes in a head-to-head “syn” arrangement, rather than the head-to-tail anti arrangement (Figure 31.20) common in most 9-substituted anthracenes [68]. Although the syn arrangement is often assumed to prevent the [4 + 4] photocycloaddition reaction due to topochemical and steric factors, solid-state NMR measurements showed that 9AC does in fact undergo the [4 + 4] cycloaddition reaction characteristic of anthracenes in the solid state [69]. The photodimer is unstable at room temperature, however, and spontaneously reverts back to the monomer state within a few minutes, which provides the desirable reversibility property. The photomechanical response appears to be reasonably robust with ~10 cycles. Photomechanical bending was also observed for 9AC nanowires coated with a thin layer of silica, although the response time was significantly slower [70]. These results show how a small change in molecular structure could lead to qualitative changes in crystal packing and also in the photomechanical behavior.
Dicopper(II) metallacyclophanes with photoswitchable oligoacene spacers: a joint experimental and computational study on molecular magnetic photoswitches
Published in Journal of Coordination Chemistry, 2018
María Castellano, Wdeson P. Barros, Jesús Ferrando-Soria, Miguel Julve, Francesc Lloret, Jorge Pasán, Catalina Ruiz-Pérez, Laura Cañadillas-Delgado, Rafael Ruiz-García, Joan Cano
In this work, we present a complementary experimental and computational study on photoswitchable long-range magnetic coupling in a family of dinuclear copper(II) metallacyclophanes with extended π-conjugated oligoacene spacers as new examples of molecular magnetic switches (MMSs). The oxamato-based dicopper(II) 2,6-anthraceno- and 1,5-naphthalenophanes exhibit an antiferromagnetically coupled to magnetically uncoupled (ON/OFF) switching behavior upon UV light irradiation and heating in the solid state. The photomagnetic bistability results from a [4+4] photocycloaddition of the two facing anthracene and naphthalene spacers. This inference is supported by molecular and electronic structure DF calculations, which evidence the lack of severe steric constraints associated with the metallacyclic structure that would preclude the formation of the resulting [4+4] photocycloaddition products of the dicopper(II) oligoacenophanes. This intramolecular (“pseudo-bimolecular”) reaction constitutes a unique example of coordination-driven self-assembly for the supramolecular control of photochemical reactivity and photophysical properties in the solid state. Current efforts are devoted to obtaining new examples of oxamato-based dicopper(II) metallacyclophanes with higher photochemical efficiency and reversibility as prototypes of photo-triggered MMSs in the emerging field of molecular spintronics.