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Photoresponsive Polymers
Published in Asit Baran Samui, Smart Polymers, 2022
By using photoactive gate dielectrics, the performance of an organic transistor can be significantly enhanced by reversibly adjusting with lights of various wavelengths. The design can be used for both types of organic transistors on a transparent substrate with the additional attribute of flexibility. Photochromic spiropyran (SP), linked to nanocarbon substrate surfaces, can be combined with conductive polymers to make photosensitive devices.129 The device conductance can be switched from one to another state by the application of UV and visible light. The reason behind the phenomenon is the reversible conformation-induced doping or proton transfer. The density functional theory calculations have established that the closed form has the electric dipole moment of 6.4 D while that of the open form is 13.9 D.130 The large change in dipole moment has the ability to change the electrostatic environment of the devices to a considerable extent. Thus, by using the photochromic SP as one component of the gate dielectric, the dielectric capacitance of the gate dielectric is changed due to illumination, which leads to modulation of the device performance. New types of ultrasensitive devices can be designed with this principle for non-invasive sensing in chemical and environmental parameters.
Stimuli-Responsive Polymer Coatings
Published in Sanjay Mavinkere Rangappa, Jyotishkumar Parameswaranpillai, Suchart Siengchin, Polymer Coatings, 2020
Fabrice Ofridam, Mohamad Tarhini, Waisudin Badri, Wei Liao, Noureddine Lebaz, Émilie Gagnière, Denis Mangin, Emilie Dumas, Sami Ghnimi, Abdelhamid Errachid El Salhi, Adem Gharsallaoui, Hatem Fessi, Abdelhamid Elaissari
For a polymer to become light responsive, a chromophore (photoresponse functional group) should be incorporated into the polymer chain. Two categories of chromophores can be found, reversible and irreversible. Reversible chromophores, upon light excitation at a specific wavelength, undertake a reversible isomerization. This allows the alteration of the properties of the host polymer by irradiation at two different wavelengths. This reversible isomerization is important in different applications such as information storage and artificial muscles [57,58]. Spiropyran, an organic molecule that upon light excitation is engaged in a photocleavage of a spiro C-O bond, was used to prepare photochromic polymer brushes. Dense and smooth polymer films were successfully prepared and used as surfaces with switchable colour and wettability by light stimulation. A specific wavelength can convert a non-polar spiropyran to a polar one, and it can be reverted to its non-polar state using visible light [59].
Crystalline Colloidal Array Photonic Crystal Optical Switching
Published in Anwar Sohail, Raja M Yasin Anwar Akhtar, Raja Qazi Salahuddin, Ilyas Mohammad, Nanotechnology for Telecommunications, 2017
Another example of a photochemically actuated PCCA is one in which photoisomerization of a covalently attached spirobenzopyran modulates the PCCA’s bandgap. Spiropobenzopyran can be photochemically cycled from its spiropyran (closed) form to its merocyanine (open, zwitterion) form. UV illumination increases the intensity of the 350 and 560 nm absorption bands, stabilizes the merocyanine form, swells the hydrogel by ~7%, and redshifts the diffraction peak by 13 nm (Figure 8.10a) (Maurer et al. 2005). Visible irradiation results in the formation of the closed-form spiropyran, which shrinks the PCCA and blueshifts the diffraction. The characteristic time for both processes is 25 min at 20 mW=cm2 UV and visible irradiation (Figure 8.10b). The characteristic thermal recovery time of the spiropyranfunctionalized PCCA in dark is 35 h at 25°C.
A photo-switchable and thermal-enhanced fluorescent hydrogel prepared from N-isopropylacrylamide with water-soluble spiropyran derivative
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Xueqing Zou, Xiaozhen Xiao, Shixiong Zhang, Jiajun Zhong, Yulin Hou, Liqiong Liao
Spiropyran and its derivatives, one type of the extensively studied photochromic dyes, have gained substantial attention owing to its high fatigue resistant photo-isomerization between ring-closing colorless spiropyran (SP) and ring-opening colored merocyanine (MC) upon the switching of Vis/UV light irradiation [13,14]. The two isomers possess different physicochemical properties such as polarity, fluorescence, and electronic properties [3,15]. Photo-switchable ‘on/off’ fluorescent transition of spiropyran has attracted great attention and could find its wide applications in super-resolution imaging, drug release, and responsive colorimetric detector [15–17]. In addition, the fluorescent behavior of spiropyran was found to be responsive to polarity [18–20], such characteristic could be harnessed in the fabrication of smart inks and biological markers. Nevertheless, the poor solubility in aqueous media, photo-degradation [21], toxicity, and relative fast fluorescence quenching [22] of spiropyran moiety have limited its accessibilities as photo-switchable fluorophores in biomedical applications. Immobilization of spiropyran via covalent attachment to a substrate is an effective approach to overcoming the aforementioned drawbacks [23–25] Spiropyran-functionalized polymers [26,27], biopolymers [28,29], inorganic nanoparticles [30,31], and hydrogel have been preferential choices for the immobilization of spiropyran [32,33].
Self-assembled molecular devices: a minireview
Published in Instrumentation Science & Technology, 2020
Spiropyran and its chemical derivatives are the most widely studied photochromic compounds. Under the ultraviolet irradiation, the closed form of spiropyran can be transformed into an open merocyanine (MC) form. Although the photochromic switch has been widely reported, the report on the photochromic switch based on spiropyran structure is rare.