Recent Development of Photochromic Polymer Systems: Mechanism, Materials, and Applications

Abstract

Photochromic polymer is defined as a series of materials based on photochromic units in polymer chains, which produces reversible color changes under irradiation with a particular wavelength. Currently, as the research progresses, it shows increasing potential applications in various fields, such as anti-counterfeiting, information storage, super-resolution imaging, and logic gates. However, there is a paucity of published reviews on the topic of photochromic polymers. Herein, this review discusses and summarizes the research progress and prospects of such materials, mainly summarizing the basic mechanisms, classification, and applications of azobenzene, spiropyran, and diarylethene photochromic polymers. Moreover, 3-dimensional (3D) printable photochromic polymers are worthy to be summarized specifically because of its innovative approach for practical application; meanwhile, the developing 3D printing technology has shown increasing potential opportunities for better applications. Finally, the current challenges and future directions of photochromic polymer materials are summarized.

Fig. 1.

Classification and applications of photochromic polymers.

Fig. 2.

(A) Properties of ABA block polymers: (A-i) schematic representation of photoreversible ion gels, (A-ii) chemical structure of the ABA triblock copolymer, (A-iii) reversible sol–gel transition cycle of the ABA triblock copolymer, and (A-iv) relationship between ionic conductivity of ABA triblock copolymer ion gels near the sol–gel transition temperature. Reproduced with permission from [40]. Copyright 2015, American Chemical Society. (B) Graphical illustrations of the photoswitchable polymer system, in which the photomechanical properties and on-demand ionic conductivity can be achieved via light irradiations. Reproduced with permission from [41]. Copyright 2023, John Wiley & Sons Inc. (C-i) Schematic diagram of synthesis of photochromic dendrimers. (C-ii) UV–vis absorption spectra of G3-Azo in tetrahydrofuran before irradiation and after UV irradiation. (C-iii) Cycling performances of G3-Azo in solution and the film under the alternative UV light and visible light irradiation. Reproduced with permission from [47]. Copyright 2020, American Chemical Society.

Fig. 3.

(A-i) Schematic description of trans-cis isomerization (Azo-LC), polymerization, cross-linking, writing, and erasing procedures. (A-ii) Spin-coated films were masked and irradiated with monochromatic green light (532 nm). (A-iii) Birefringence pattern formed when UV light irradiates the film. Reproduced with permission from [52]. Copyright 2023, American Chemical Society. (B-i) Chemical structures of PNB-Azo-100. (B-ii) Application of azobenzene light patterning. Reproduced with permission from [53]. Copyright 2021, Elsevier Ltd. (C-i) Structure of polymer NPs. (C-ii) Polymer NPs for cancer therapy. Reproduced with permission from [58]. Copyright 2020, Royal Society of Chemistry. (D-i) Chemical structures of PPNPs, PAPESE, and N-succinyl chitosan. (D-ii) Schematic illustration of cytotoxicity and genotoxicity of azobenzene-based polymeric nanocarriers for phototriggered drug delivery in biomedical applications. Reproduced with permission from [61]. Copyright 2022, Licensee MDPI.

Fig. 4.

(A-i) Chemical structures and photoisomerization of azobenzene-containing polyacrylate P-H and polymethacrylate P-Me. (A-ii) AFM height images of P-H and P-Me films with a scratch before irradiation, after UV irradiation (365 nm, 12.8 mW cm^–2), and after subsequent visible light irradiation (530 nm, 19.9 mW cm^–2) for 2 cycles. Reproduced with permission from [62]. Copyright 2023, American Chemical Society. (B-i) Chemical structure and photoresponsive properties of the azopolymer P1. (B-ii) Reversible solid–liquid transition healing through light-induced transformation. Reproduced with permission from [63]. Copyright 2020, John Wiley & Sons Inc.

Fig. 5.

(A-i) Change in UV−vis spectra of SP-loaded (PS-b-P4VP/PS-b-PAA) multilayer films with increasing UV irradiation time at 365 nm. (A-ii) Light transmission curve of (PS7K-b-P4VP/PS-b-PAA) multilayer films before and after UV irradiation. Reproduced with permission from [67]. Copyright 2006, American Chemical Society. (B) Schematic of optical nanoimaging for microphase structures of BC self-assembly. Reproduced with permission from [72]. Copyright 2015, American Chemical Society. (C-i) Chemical structure of the polymer. (C-ii) Mechanochromism in semicrystalline polymers. Reproduced with permission from [73]. Copyright 2023, John Wiley & Sons Inc. (D) Photochromic polymers with photoswitching properties. Reproduced with permission from [74]. Copyright 2015, American Chemical Society. (E) Preparation of the functional photochromic latex particles containing SP by emulsifier-free emulsion polymerization. Reproduced with permission from [21]. Copyright 2018, American Chemical Society.

Fig. 6.

(A) Application of the functionalized stimuli-responsive latex particles (CLB-SP) as an anti-counterfeiting and rewritable smart ink for secured marking in security documents. Reproduced with permission from [21]. Copyright 2018, American Chemical Society. (B) Security printing of photoluminescent and photochromic anti-counterfeiting inks on confidential documents such as banknotes and passports. Reproduced with permission from [78]. Copyright 2023, Elsevier Ltd. (C) Printed optical security tags by using photoluminescent and photochromic NPs containing SP (FPMCNPs-SPOH); the photography was carried out before, during, and after UV light illumination (365 nm). Reproduced with permission from [88]. Copyright 2023, American Chemical Society. (D-i) Color and fluorescent images of C1 and C2 powder. (D-ii) Schematic illustration of write-erase cycles carried out on films containing C1 and C2 Reproduced with permission from [87]. Copyright 2021, Elsevier Ltd. (E-i) Schematic illustration of photoswitching behavior of PFPNs under UV and visible light irradiation. (E-ii) Photoinduced switching cycles of PFPNs (NP-N3) under alternative illumination of UV for 3 min and visible light for 5 min (λ_ex = 410 nm, 25 °C). Reproduced with permission from [91]. Copyright 2017, Royal Society of Chemistry. (F-i) Reversible structure isomerization of BOSA-SP and BOSA-MC. (F-ii) UV/Vis absorption spectra of BOSA-SP powders before and after UV irradiation. (F-iii) Green and (F-iv) red conventional fluorescence and super-resolution imaging of the cross-sectional profiles of the PSt-b-PEO cylindrical micelles at the dashed lines of the microscopy images. (F-v) Polymer super-resolution imaging applications. Reproduced with permission from [92]. Copyright 2022, John Wiley & Sons Inc.

Fig. 7.

(A-i) Photochromism before, under, and after UV irradiation (365 nm) for the (1) PMMA, (2) PMMA-co-PHEMA, and (3) PMMA-co-PDMAEMA NPs. The pH of all the samples is 1, 3, 7, 10, and 14, from left to right, respectively. (A-ii) The coloration of the photochromic cellulosic papers under UV (365 nm) and visible light irradiation in neutral and acidic conditions. Reproduced with permission from [93]. Copyright 2022, American Chemical Society. (B-i) Synthetic scheme of ion-hybrid cross-link photochromic hydrogels. (B-ii and iii) tensile stress–strain curves of P(SA-co-MA-co-SPMA)/Ca²⁺ photochromic hydrogels soaked in solutions at different Ca²⁺ concentrations. (B-iv) The process of rewritable imaging on the P(SA-co-MA-co-SPMA)/Ca²⁺2.7 M hydrogel by using UV light. Reproduced with permission from [94]. Copyright 2021, John Wiley & Sons Inc. (C-i) Schematic representation for preparation of MBSP NPs and the corresponding stimuli-responsive nanofibers with color changes. (C-ii and iii) Diameter distribution of 2 types of nanofibers. (C-iv) Images of the MBSP@NF sheet before and after exposure to HCl and ammonia vapors using “HCL” and “NH₃” patterns in their visual mode. Reproduced with permission from [95]. Copyright 2020, American Chemical Society.

Fig. 8.

(A-i) Illustration of the synthesis of DPP-1 and DPP-2 by the Schiff-base polycondensation reaction. Time-dependent UV–vis–NIR absorption spectral changes of (A-ii) DPP-1 and (A-iii) DPP-2 upon irradiation with 365-nm light. Reproduced with permission from [100]. Copyright 2019, Royal Society of Chemistry. (B-i) Structures of photochromic DAEs as guest molecules (DAE, DAE-Male1, DAE-Male2, DAE-Male3, and DAE-NHS). (B-ii) Structure of a cucurbit [7] uril host molecule (CB7), (B-iii) DFT-optimized geometry and the photoswitching reaction of the DAE@CB7 complex. Reproduced with permission from [101]. Copyright 2022, American Chemical Society. (C) The construction of the photochromic SCP, and the chemical structures of corresponding components. FRET, fluorescence resonance energy transfer. Reproduced with permission from [102]. Copyright 2021, Springer Nature. (D) Photoisomerization of DTEDBA and Cu-DTEDB. Reproduced with permission from [105]. Copyright 2016, John Wiley & Sons Inc. (E) Reversible bending of a crystalline rod. Reproduced with permission from [103]. Copyright 2007, Springer Nature.

Fig. 9.

(A-i) Schematic illustrations of the design strategy from 2 photochromic fluorescent monomers to a photoswitchable multistate fluorescent polymer. (A-ii) The photoswitchable multistate fluorescent polymer can reversibly switch between multiple emission states (nonemission, red and green). (A-iii) Polymeric solid films for multi-information encryption and advanced anti-counterfeiting. Reproduced with permission from [109]. Copyright 2021, Elsevier Ltd. (B) Schematic diagram of PMFSPs: (B-i) photochromism of CDSP and SDTE, (B-ii) preparation of PMFSP films, and (B-iii) information encryption applications of PMFSPs. Reproduced with permission from [110]. Copyright 2023, American Chemical Society. (C) Device structure of optical switchable transistors. Reproduced with permission from [111]. Copyright 2023, John Wiley & Sons Inc. (D) Incooperation of diaryl-HI 4b into a PS polymer and resulting photochromic behavior of the transparent material. Reproduced with permission from [112]. Copyright 2023, Springer Nature.

Fig. 10.

(A-i) Formation and photoinduced isomerization of the coordination polymer. (A-ii) Schematic interconversion of the multistability of the iron metallopolymer switch; for more information about the chemical structure, (A-iii) top: schematic presentation of a 2:1 multiplexer, bottom: performance of poly (FeII-Lo)⁴⁺ as a 2:1 multiplexer and truth table. Reproduced with permission from [117]. Copyright 2022, American Chemical Society. (B-i) Component self-assembly of photoresponsive A₂L₃M₂ (A = A1 or A2, M = ZnII or CdII) metal-templated cage and UV/vis induced ring-opening/closing behaviors in PADTE. (B-ii) Cycled signals for absorbance at 627 nm during alternate ring-closing/opening processes. (B-iii) Polymer photochromic photos. Reproduced with permission from [118]. Copyright 2020, Royal Society of Chemistry. (C) Combined logic gate application before and after UV multiple-stimulation response: photographs of patterns assembled from multicolored hydrogels on black substrates. Reproduced with permission from [119]. Copyright 2023, John Wiley & Sons Inc. (D-i) Schematic representation of the PCL NPs doped with DBTEO and HPNIC and their photoswitching reaction by UV/visible-light irradiations. (D-ii) Photoluminescence (PL) spectra changes of the PCL NP containing DBTEO and HPNIC upon UV and visible light irradiations. (D-iii) Reversibility test of the NP with alternation of UV and visible light irradiations. (D-iv) Polymer bioimaging applications. Reproduced with permission from [125]. Copyright 2019, Springer Nature.

Fig. 11.

(A-i) Photoresponsive pictures of the printed hollow 3D structures containing different mass fractions of TrPEF₂-MA. (A-ii) Schematic of the 3D-printed multicomponent framework for the information carrying and encryption. Reproduced with permission from [136]. Copyright 2022, American Association for the Advancement of Science. (B) Schematic illustration of the writing, reading, and erasing of optical information in the transparent Eu-Ag germanium borate glass. Reproduced with permission from [140]. Copyright 2022, American Chemical Society. (C-i) 3D printing formulation composition. (C-ii) Increase in absorption at λ_max = 801 nm due to photoreduction of the encapsulated [C₁₀POM] upon exposure to the projected light over time, and the inset shows the corresponding UV–vis spectra. (C-iii) Information encoded by photoreduction could be erased and reprinted several times, as evidenced by a change in the absorbance intensity at λ_max = 801 nm upon cycles of photoreduction (encoding) and oxidation (erasure). (C-iv) 3D printed structure accuracy and changes before and after UV irradiation. Reproduced with permission from [137]. Copyright 2018, John Wiley & Sons Inc. (D-i) Schematic depiction of the photoisomerization of a DASA-containing network. (D-ii) Schematic of direct laser writing using a C60-shaped CAD model. (D-iii) Microstructural microscopic images of 3D structures at different time points after laser excitation. Reproduced with permission from [138]. Copyright 2021, John Wiley & Sons Inc.