Open‐shell Poly(3,4‐dioxythiophene) Radical for Highly Efficient Photothermal Conversion

Abstract

Open‐shell organic radical semiconductor materials have received increasing attention in recent years due to their distinctive properties compared to the traditional materials with closed‐shell singlet ground state. However, their poor chemical and photothermal stability in ambient conditions remains a significant challenge, primarily owing to their high reactivity with oxygen. Herein, a novel open‐shell poly(3,4‐dioxythiophene) radical PTTO₂ is designed and readily synthesized for the first time using low‐cost raw material via a straightforward BBr₃‐demethylation of the copolymer PTTOMe₂ precursor. The open‐shell character of PTTO₂ is carefully studied and confirmed via the signal‐silent ¹H nuclear magnetic resonance spectrum, highly enhanced electron spin resonance signal compared with PTTOMe₂, as well as the ultra‐wide ultraviolet‐visible‐near nfraredUV–vis–NIR absorption and other technologies. Interestingly, the powder of PTTO₂ exhibits an extraordinary absorption range spanning from 300 to 2500 nm and can reach 274 °C under the irradiation of 1.2 W cm⁻², substantially higher than the 108 °C achieved by PTTOMe₂. The low‐cost PTTO₂ stands as one of the best photothermal conversion materials among the pure organic photothermal materials and provides a new scaffold for the design of stable non‐doped open‐shell polymers.

The stable poly(3,4‐dioxythiophene) radical PTTO₂ is reported for the first time, exhibiting a narrow band gap of 0.82 eV and an electron conductivity of 3.11 × 10⁻⁴ S cm⁻¹, surpassing those of closed‐shell P3HT and doped PEDOT. Under irradiation at 1.2 W cm⁻², the temperature of PTTO₂ powder can reach 274 °C, representing one of the highest photothermal conversion performances among organic photothermal materials.

1. Introduction

Organic semiconductive polymers based on polythiophenes (PTs) have been the subject of extensive research for over three decades owing to their straightforward structure, convenient synthesis, and wide application in various fields.^{[ 1} , ² , ^{3 ]} Poly(3‐hexylthiophene) (P3HT) and poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) stand out as two globally recognized materials among the multitude of organic semiconductive polymers (Figure  1a). P3HT, featuring n‐hexyl side chains on each thiophene ring, shows high solubility, excellent solution‐processibility, relatively high crystallinity and hole mobility, which endow it with great application potential in organic electronic devices, perovskite solar cells, and other fields.^{[ 4} , ⁵ , ⁶ , ^{7 ]} Throughout the development of PTs, the researchers have devised various strategies to modify P3HT to further enhance its charge transport properties.^{[ 8} , ^{9 ]} However, it is still challenging to achieve high conductivity of P3HT derivatives due to their inherent limitations in hole mobility and charge concentration in these neutral semiconductive polymers. In contrast to P3HT, PEDOT: PSS shows extraordinarily high conductivity as it is a doped polythiophene cationic radical with a low band gap and open‐shell ground state.^{[ 10} , ¹¹ , ¹² , ^{13 ]} Capitalizing on its exceptional conductivity and solution‐processibility, PEDOT: PSS has shown widespread application as interface material and transparent electrode for organic electronic devices such as organic light‐emitting diodes, organic solar cells, perovskite solar cells, as well as in large‐scale industrial applications in the antistatic, capacitor, printed circuit board and other fields.^{[ 14} , ¹⁵ , ¹⁶ , ¹⁷ , ^{18 ]} However, the water dispersibility, strong acidity caused by the PSS dopant, and relatively low work function (WF) of PEDOT: PSS will inevitably degrade the photoelectric devices to some extent.^{[ 19} , ^{20 ]}

Figure 1.

a) The chemical structure and properties of P3HT, PEDOT: PSS and PTTO₂. b) The synthesis route, the density functional theory calculation on the molecular configuration of PTTOMe₂ and PTTO₂, and the non‐covalent intramolecular conformation lock in red dotted line.

It is noteworthy and interesting that the undoped organic radicals materials, such as the non‐conjugated 2,2,6,6‐tetramethylpiperidinooxy (TEMPO)‐based polymer, have displayed high conductivity of 0.28 S cm⁻¹ and have been rapidly developed in recent years due to their unique charge transport mechanism.^{[ 21} , ^{22 ]} Moreover, the classical donor‐acceptor (D‐A) materials also exhibited high conductivity.^{[ 23} , ²⁴ , ^{25 ]} Since 2017, we initially discovered and reported that the classical low‐bandgap D‐A organic semiconductors and P3HT showed widespread open‐shell quinoid‐diradical resonance structure with tunable singlet and triplet ground states, which make them unstable in air.^{[ 26} , ²⁷ , ²⁸ , ²⁹ , ^{30 ]} Nevertheless, the synthesis of these radical materials is relatively complex, their chemical and photothermal stability plays a key role in their practical application due to their high spin concentration and reactivity from strong electronic interactions of radical species.^{[ 31} , ^{32 ]} Herein, we propose a novel design strategy for preparing non‐doped poly(3,4‐dioxythiophene) via introducing the oxygen radical onto the conjugated backbone of PTs (Figure 1a). Intriguingly, the neutral radicals showed high chemical stability without the protection of large steric hindrance groups due to the resonance structure between their oxygen radical and the highly electron‐withdrawing carbonyl structure.^{[ 33} , ³⁴ , ³⁵ , ^{36 ]} In addition, stable radical‐based organic materials exhibit unique optical properties, such as near‐infrared (NIR) absorption and non‐radiation decay from a photoelectric excited state, which can sufficiently convert sunlight into heat energy, thus realizing efficient photothermal conversion.^{[ 37} , ³⁸ , ^{39 ]}

In detail, we comprehensively considered the advantages of PTs and organic open‐shell radicals in terms of low cost and convenient synthesis. Accordingly, PTTOMe₂ was rationally designed and prepared via one‐step stille‐coupling polymerization and PTTO₂ was readily obtained via demethylation with BBr₃(99.9%) at room temperature in air (Figure 1b). The polymeric PTTO₂ radical demonstrated significantly enhanced photothermal conversion performance compared with its precursor PTTOMe₂. Under the irradiation of an 808 nm laser at a power density of 1.2 W cm^{− 2}, the temperature of PTTO₂ powder achieved 274 °C within 60 s. Meanwhile, it showed a high‐water evaporation rate of 1.206 kg m⁻² h⁻¹ and solar energy‐to‐vapor efficiency of 83.3% upon one sun irradiation, standing as one of the best pure organic photothermal materials with low cost.

2. Results and Discussion

The copolymer PTTOMe₂ was prepared via the one step simple Stille coupling polymerization using 2,5‐dibromo‐3,4‐dimethoxythiophene and 2,5‐bis(trimethylstannyl)thiophene (Figure 1b) as the raw materials. The PTTO₂ was obtained via a facile and efficient demethylation reaction of PTTOMe₂ in a dichloromethane (DCM) solution with BBr₃ (98%) as a reactant (Figure 1b). The structures of both PTTOMe₂ and PTTO₂ were confirmed by ¹H nuclear magnetic resonance (¹H‐NMR) spectra (Figures S1 and S2, Supporting Information), Maldi‐tof spectrometry (Figures S3 and S4, Supporting Information) and Fourier transform infrared (FT‐IR) (Figure S5, Supporting Information). It is worth mentioning that PTTO₂ exhibits a unique property, namely the disappearance of ¹H NMR spectral signals in solution, which can be attributed to the presence of PTTO₂ radicals in solution. Figures S3 and S4 (Supporting Information) showed fragment ions with different masses. Notably, the high reactivity of radicals facilitates their facile binding with metal ions. Therefore, when conducting a structural analysis of PTTO₂, it is essential to consider the potential coordination of PTTO₂ with metal ions, as this interaction can significantly influence the properties of a compound.^{[ 40 ]} In addition, we confirmed the successful demethylation of PTTOMe₂ via FT‐IR as the observation of the disappearance of the methyl signal (3000–2800 cm⁻¹). An energy dispersive spectroscopy (EDS) analysis revealed that the atomic percentages of boron (B) and bromine (Br) elements in PTTO₂ were 0.60% and 0.61%, respectively, suggesting that negligible ion doping occurred during the demethylation process of PTTOMe₂ to produce PTTO₂ (Figure S6, Supporting Information). Elemental analysis (EA) was carried out to further verify the experimental results (Table S3, Supporting Information). The measured C, O, and S contents in the PTTOMe₂ sample are 52.32%, 16.48%, and 28.38%, respectively, closely matching the theoretical values (C, 53.55%; O, 14.27%; S, 28.59%). In the case of PTTO₂, the measured C, O, and S contents were 48.41%, 19.30%, and 28.09%, respectively, with a notable decrease in the carbon content compared to PTTOMe₂, aligning with the theoretical prediction of 49.47% for C content.

The thermal stability of PTTOMe₂ and PTTO₂ polymers was investigated through thermogravimetric analysis (TGA) to determine the thermal decomposition temperature (T_d ). The two powder samples were placed in a crucible under a thermogravimetric analyzer under a nitrogen atmosphere. Thermogravimetric curves were recorded for both materials at a heating rate of 10 °C min⁻¹ (as shown in Figure S7, Supporting Information). The 5% weight loss temperature for PTTOMe₂ and PTTO₂ were found to be 333 °C and 268 °C, respectively. The relatively low T_d values may be attributed to the relatively low molecular weight of the polymers. Additionally, the differential scanning calorimetry (DSC) results indicated a glass transition temperature (T_g ) of 86 °C for PTTOMe₂. In contrast, PTTO₂ did not exhibit any clear thermal transitions during the test process, suggesting an absence of both a distinct glass transition and crystallization behavior (Figure S8, Supporting Information).

Density functional theory (DFT) calculations based on Gaussian at a B3LYP/6‐31G (d, p) level were utilized to probe the conformational characteristics of the polymer and the polymer skeleton is represented by two repeat units (Figure 1b). The calculated dihedral angles between adjacent units along the main chain of PTTOMe₂ are 3.04°, 2.50°, 2.38°, 2.31°and 3.18°, respectively. Besides, the dihedral angle calculation results of PTTO₂ revealed a strikingly planar structure. According to the reported work, the planar configuration of PTTO₂ comes from the noncovalent bond effect between sulfur and oxygen of the thiophene backbone. This result can also explain the extremely poor solubility of PTTO₂.^{[ 41} , ^{42 ]}

The optical absorption properties of PTTOMe₂ and PTTO₂ were studied by UV–vis absorption spectra in Figure  2a. The UV–vis absorption spectra of both PTTOMe₂ and PTTO₂ in solution or thin film all displayed typical sharp absorbance bands between 300 and 600 nm, which can be well identified as the absorption of conjugated polythiophene backbone. In addition, the solution of PTTO₂ in DMSO exhibited a wide absorption band between 600 and 1500 nm, indicating the contribution of the open‐shell PTTO₂ radical in the solution, which has been similarly reported in previous work.^{[ 43} , ⁴⁴ , ⁴⁵ , ^{46 ]} Compared with PTTO₂ in solution state with an absorption edge ≈1380 nm, the film of PTTO₂ showed an absorption edge approaching 1520 nm, indicating a lower band gap due to the aggregation effect. The characteristic radical peaks observed in the PTTO₂ film are associated with an aggregation‐induced radical (AIR) effect.^{[ 26} , ²⁷ , ²⁸ , ²⁹ , ^{30 ]} Specifically, the radicals are easily combined with trace water in a solution to form hydroxyl groups, while the quinone radicals are conducive to being produced in a film due to the AIR effect, pancake bond formation, and π–π stacking.^{[ 29} , ³⁰ , ^{47 ]} Accordingly, the optical bandgaps of PTTOMe₂ and PTTO₂ in film are 1.82 and 0.82 eV, respectively. These results indicate that the design of the open‐shell PTTO₂ is a facile and efficient strategy to decrease the band gap of PT polymers.

Figure 2.

a) UV–vis–NIR absorption spectra and photoluminescence spectra in solution as well as film. b) Electron paramagnetic spectra of the PTTOMe₂ and PTTO₂ powder (0.02 mmol). c) UV–vis–NIR spectrum of PTTOMe₂ and PTTO₂ in powder compared with inorganic materials (diffuse reflection mode). d) Cyclic voltammetry curves of PTTOMe₂ (in solution) and PTTO₂ (in film) with Hg/Hg₂Cl₂ electrode as reference. Potential values are reported with the saturated calomel electrode as the reference electrode using the Fc⁺/Fc couple (0.317 V) as an internal standard.

The photoluminescence (PL) spectra of PTTOMe₂ and PTTO₂ are shown in Figure 2a. In the solution state, the PL spectra of PTTOMe₂ in DCM and PTTO₂ in DMSO showed peaks ≈583 and 562 nm, respectively. The PL of PTTO₂ in the DMSO solution originates from the hydroxyl polymer PTTOH₂ due to the reaction of PTTO₂ radicals with the trace water. The spin‐coated film of PTTOMe₂ showed weak dark‐red emission ≈675 nm, whereas the PL of the corresponding PTTO₂ radical in the film is quenched. The results are in good agreement with the previous reports indicating that the radical materials usually show extremely low photoluminescence quantum yields (PLQYs) and negligible radiation decay of PTTO₂ in the solid state.^{[ 26} , ²⁷ , ²⁸ , ²⁹ , ^{30 ]} The nonradiative decay will be largely boosted due to the open‐shell quinoidal radical structure, which will enhance the photothermal conversion efficiency with the promising application potential of PTTO₂ in the solid state.^{[ 33} , ^{48 ]}

To further explore the open‐shell radical structure of PTTO₂, the radical characters of the two polymers were characterized via the electron spin resonance (ESR) spectrum. Under the same test condition, the powder of the polymer PTTOMe₂ showed almost none of the paramagnetic signal. In contrast, a significant increase in the ESR signal of PTTO₂ was detected after the demethylation of the corresponding methoxy precursors (Figure 2b). The hydroxyl groups generated after the demethylation of the red PTTOMe₂ are readily oxidized into the black PTTO₂ radicals by oxygen in the air at room temperature, resulting in the production of oxygen radicals and enhanced ESR signal, which is consistent with the results obtained from ¹H‐NMR, FTIR, EDS, and elemental analysis test.^{[ 42} , ^{43 ]} In general, the high spin concentration of the open‐shell PTTO₂ is beneficial for the non‐radiative transitions to improve photothermal conversion capability.^{[ 49} , ^{50 ]}

Then, we performed solid‐state UV–vis–NIR absorption spectroscopy experiments using the diffuse reflection technique at room temperature, and the results are presented in Figure 2c. PTTO₂ showed a broader light absorption range compared with that of PTTOMe₂, owing to the strong electronic tunneling coupling between the neighboring radical molecules.^{[ 37 ]} Different from the UV–vis absorption spectra in solution, the absorption spectra of the PTTO₂ extend from 300 to 2500 nm in the powder state (Figure 2c), similar to the graphene, carbon black, and Fe₃O₄, covering the entire solar spectrum, indicating that the intermolecular interaction in the solid state can greatly promote its extended wavelength absorption.^{[ 37 ]} The absorption of PTTO₂ powder is much broader than those of previous pure organic materials (Figure 4c).^{[ 35} , ³⁸ , ³⁹ , ⁴⁴ , ⁵¹ , ⁵² , ^{53 ]} These results demonstrate that PTTO₂ powder can absorb most of the UV–Vis and near‐infrared light, which is consistent with its black appearance.

Figure 4.

a) The Jablonski diagram shows the difference in energy dissipation of excited states to understand the different photothermal conversion efficiency of PTTOMe₂ and PTTO₂. b) Intermolecular chain interaction and photothermal conversion. c) The comparison of absorption edge between pure‐organic small molecules and polymers in powder. d) The temperature change of PTTOMe₂ and PTTO₂ under different power densities of the laser. The photothermal conversion performance of PTTOMe₂ and PTTO₂ comparing the previously reported pure organic photothermal materials in solid state at different power densities and wavelengths.

To study the electrochemical characteristics and energy level of the two polymers, the cyclic voltammetry (CV) test was conducted in the air using n‐Bu₄NPF₆ as the supporting electrolyte in dry acetonitrile solution and Hg/Hg₂Cl₂ as reference electrode (Figure 2d). The highest occupied molecular orbital (HOMO) energy level of each polymer sample is calculated by intercepting the inflection point of the single‐loop CV curve. The HOMO of PTTOMe₂ and PTTO₂ are recorded as −4.85 and −5.14 eV, respectively, indicating that the demethylation can efficiently lower the HOMO energy level. Both the solution and powder of PTTO₂ in the air are stable for several months due to its deeper HOMO level compared with that of PTTOMe₂. The structure of PTTO₂ is similar to that of o‐quinone (Figure 1b), and the two resonance carbonyl groups with strong electron acceptor character contribute to its relatively lower HOMO energy level than that of PTTOMe₂. In the future, we will apply this strategy to introduce electron‐deficient acceptor groups to further reduce the HOMO level and alkyl chains to enhance the solubility and solution‐processability of PTTO₂‐based low HOMO polymers. Consequently, the conductivity of PTTO₂ thin film was measured using the four‐probe meter, and the average value of PTTO₂ was 3.11 × 10⁻⁴ S cm⁻¹ (Table 1 ), which is two times higher than the 1.26 × 10⁻⁴ S cm⁻¹ of PTTOMe₂ and comparable with 1 × 10⁻⁴ S cm⁻¹ of PEDOT: PSS‐4083, widely applied in organic electronic devices and other fields. The relatively high electrical conductivity of PTTO₂ can be understood by the introduction and interaction of oxygen radicals within its planar structure.^{[ 46} , ⁵⁴ , ^{55 ]} We propose that the electrical conductivity can be further enhanced by improving the molecule weight by the copolymerization of the (3,4‐dioxythiophene) radical with other highly soluble and conjugated donor and acceptor building blocks in the future.^{[ 56} , ^{57 ]}

Table 1.

Optical and electrochemical properties and energy levels of radicals and corresponding precursors.

Sample	λabs sol (nm) a)	λabs film (nm) b)	λemi sol (nm) c)	λemi film (nm) d)	Eg opt (eV) e)	Eox, onset (eV) f)	HOMO (eV) g)	Conductivity (10−4 S cm−1)
PTTOMe2	569	682	583	675	1.82	0.37	−4.85	1.26
PTTO2	1380	1520	562	‐	0.82	0.66	−5.14	3.11

^a) λ_abs is the wavelength of the absorption edge of samples in solution;

^b) λ_abs is the wavelength of the absorption edge of samples in thin film;

^c) λ_emi is the wavelength of the emission peak of samples in solution;

^d) λ_emi is the wavelength of the emission peak of samples in thin film;

^e) E_g ^opt = 1240/λabsfilm;

^f) From the oxidation onset potential of PTTOMe₂ solution in DCM and PTTO₂ film, respectively;

^g) E_HOMO = (E_{ox, onset} + 4.8 − E_Fc/Fc+) eV.

Next, to evaluate the photothermal conversion performances of PTTOMe₂ and PTTO₂, an infrared camera was applied to monitor the temperature change of their powders under 808 nm laser irradiation. Figure  3a,b shows the rising and cooling process of PTTOMe₂ and PTTO₂ under the irradiation of 808 nm laser at different power densities. When the power density increased by 0.2 W cm⁻², the temperature of PTTO₂ powder rose synchronously by more than 35 °C, which represents a high photothermal conversion performance, showing fast and sensitive photothermal response behavior.^{[ 44 ]} The temperature of PTTO₂ powder achieved 274 °C under continuous irradiation at a power density of 1.2 W cm⁻² power for 1 min (Figure 3c). This result is consistent with the enhanced electronic paramagnetic signal of PTTO₂ observed in the electron paramagnetic resonance spectrum. It is noteworthy that the relationship between the platform temperature and power density of PTTO₂ is approximately linear, while PTTOMe₂ shows irregular changes. The enhanced photothermal conversion can be attributed to the introduction of oxygen radicals in PTTO₂ through the plasmon resonance effect similar to previous work.^{[ 58} , ^{59 ]} The generation of radicals can promote the process of electroacoustic interconversion, increase the number of phonons, and further convert the optical radiation energy absorbed by electrons into heat energy through thermal radiation, to improve the photothermal conversion efficiency.^{[ 46} , ⁵⁸ , ^{59 ]}

Figure 3.

a,b) Photothermal conversion behavior of PTTOMe₂ and PTTO₂ powder (20 mg) under 808 nm laser irradiation at different laser powers (0.2–1.2 W cm⁻²) (Insert: Digital photos of PTTOMe₂ and PTTO₂ powder, respectively). c) Anti‐photobleaching property of PTTOMe₂ and PTTO₂ powder during ten cycles of heating–cooling processes under the 1.2 W cm⁻² power. d) Linear fitting of platform temperature and power density. e) Infrared thermal images of PTTO₂ powder under 808 nm laser irradiation (1.2 W cm⁻²). f) Photothermal conversion behavior of PU, PTTOMe₂+PU and PTTO₂+PU foams under 1 sunlight irradiation (1.0 kW m⁻²). g) The temperature changes of PU, PTTOMe₂+PU, and PTTO₂+PU foams floating on water against sunlight irradiation time. (Insert: Digital photos of PU, PTTOMe₂+PU, and PTTO₂+PU foams, respectively). h) Water evaporation curves with PU, PTTOMe₂+PU and PTTO₂+PU foams under simulated sunlight with an intensity of 1.0 kW m⁻².

Then, we also measured the multi‐circle photothermal cycle curves of PTTO₂ to study the photothermal stability (Figure 3d). During the ten cycles of heating and cooling, the PTTO₂ showed negligible temperature change, showing good photothermal stability and photobleaching resistance. The outstanding photothermal conversion properties and stability of PTTO₂ result from its broad NIR absorption, promoted nonradiative decay, and relatively deep HOMO energy level.^{[ 39 ]} The low‐cost open‐shell radical polymer PTTO₂ demonstrates great potential for solar thermal conversion compared to other pure organic photothermal conversion materials.^{[ 51} , ⁶⁰ , ⁶¹ , ⁶² , ^{63 ]}

Considering the high efficiency of solar energy collection and broad absorption spectrum from 300 to 2500 nm of PTTO₂ powder, solar driven water evaporation was carried out to study the photothermal properties of the radical polymers. We employed a commercially available white porous polyurethane (PU) foam with low thermal conductivity as support to establish an efficient interfacial evaporation system by floating the polymer‐loaded PU foam on water.^{[ 33 ]} The two polymers were loaded (10 mg) inside the PU foam by impregnating pure PU foam in solution and drying, obtaining a brownish‐black PU foam (Figure 3g). The surface temperature of the blank PU foam, PTTOMe₂+PU, and PTTO₂+PU were recorded under 1 sun (1 kW m⁻²) irradiation in air and presented in Figure 3f. After irradiating the dry material‐loaded sponge for 10 min, the temperatures of PTTOMe₂ and PTTO₂ reached 66.8 °C and 82.8 °C, respectively, exhibiting the fast response to solar light which contributes to the photothermal conversion. In Figure 3g, the temperatures of PTTOMe₂+PU and PTTO₂+PU foam floating on the water reached 38.1 °C, and 42.8 °C, respectively, after 1 h of 1 sun irradiation, which is higher than that of the PU foam of 32.3 °C.

The mass change curves of PU foams in water were recorded to assess solar‐driven interfacial water evaporation efficiency (Figure 3h). The PTTO₂ demonstrates greater mass change and a sharper slope than that of PTTOMe₂, showing an evaporation rate as high as 1.206 kg m⁻² h⁻¹ and the solar‐driven water evaporation efficiency (η) of 83.3% under 1 sun illumination (see the detailed calculation process in Supporting Information). These experimental results further confirmed the enhanced photothermal conversion efficiency of the PTTO₂ radical compared to PTTOMe₂, because the generation of radicals increases photothermal conversion performance (Figure  4a,b). Compared with the previously reported pure organic photothermal materials, PTTO₂ exhibits superior photothermal conversion performance (Figure 4c,d; Table S5, Supporting Information). In addition, the synthesis cost of PTTO₂ is relatively low compared with previously published pure‐organic photothermal conversion materials (Table S4, Supporting Information), indicating the advantages and promising potential of PTTO₂ for large‐scale production in the future.

3. Conclusion

In summary, the two new polymers PTTOMe₂ and open shell polyradical PTTO₂ were prepared via two‐step simple reaction using low‐cost raw materials. Compared with PTTOMe₂, PTTO₂ exhibited enhanced electronic conductivity of 3.11 × 10⁻⁴ S cm⁻¹, lower HOMO energy level and band gap of 0.82 eV in film, and broadened absorption between 300 and 2500 nm in powder. The continuous irradiation of the PTTO₂ powder under the power of 1.2 W cm⁻² in 1 min can elevate its temperature to 274 °C. The enhanced paramagnetic property of PTTO₂ plays a key factor in its high photothermal conversion performance. This study provides a new poly(3,4‐dioxythiophene) radical backbone for the design and facile preparation of stable polymeric radical materials with potential application prospects in interfacial water evaporation, biomedicine, and other fields.^{[ 26} , ⁶⁴ , ⁶⁵ , ^{66 ]} More interestingly, this work paved the way for the design and synthesis of low bandgap non‐doped polymers with low‐cost raw materials. Based on this, the synthesis and application of the highly soluble stable open‐shell small molecule and polymers with higher photothermal conversion efficiency based on the 3,4‐dioxythiophene radical are in urgent progress in our lab.^{[ 26} , ²⁷ , ²⁸ , ⁶⁷ , ⁶⁸ , ⁶⁹ , ⁷⁰ , ⁷¹ , ⁷² , ^{73 ]}

Conflict of Interest

The authors declare no conflict of interest.

Supporting information

Supporting Information

Wei Q., Huang J., Meng Q., Zhang Z., Gu S., Li Y., Open‐shell Poly(3,4‐dioxythiophene) Radical for Highly Efficient Photothermal Conversion. Adv. Sci. 2024, 11, 2406800. 10.1002/advs.202406800

Data Availability Statement

The data that support the findings of this study are available in the supplementary material of this article.