Optical Modulation of Nematic and Cholesteric Reactive Mesogens via Two-Photon Lithography

The modulation of the optical response of structures fabricated in reactive mesogens (RMs) has proven to be a versatile and innovative strategy in creating polymeric devices with the tailored optical properties typical of liquid crystals. [1-3] Among the fabricating techniques, two-photon lithography (TPL) stands out as one of the most suitable technologies for producing complex 3D objects with high sub-wavelength resolution [4] and, at the same time, it allows us to modify the RMs' internal architecture. Here, we show how the nematic phase is perturbed when TPL is performed along an angle that is not parallel or perpendicular to the director vector, resulting in the reordering of RMs. This leads to a reorientation of the optical axis and birefringence, which can be finely controlled in terms of the writing parameters (i.e., laser power, scan speed, periodicity). Similar studies performed on cholesteric RMs aim to demonstrate the possibility of fabricating devices with customizable photonic band gaps across the entire visible spectrum, simply by tuning the energy dose delivered during manufacturing [5]. A further modulation of the optical device response can be achieved through temperature control. [6] These studies are exploited to fabricate innovative security devices that cannot be replaced with other technologies or materials. References: [1] H. Zeng et al. Adv. Mater., 2014, 26, 15, 2319. [2] A. M. Flatae et al., Light Sci., 2015, Appl. 4, 4, e282. [3] R. Wei et al. Macromol. Rapid Commun., 2013, 34, 4, 330. [4] S. Engelhardt, Direct Laser Writing. In Laser Technology in Biomimetics; V. Schmidt, M. R. Belegratis, Eds.; Springer-Verlag, Berlin/Heidelberg 2013. [5] T. Ritacco et al, Adv. Optical Mater., 2021, 2101526. [6] T. Ritacco et al, Liquid Crystals., 2024, 1,9.