Enlightening the future: AIEgen-integrated phthalocyanines and subphthalocyanines for next-generation functional materials

Abstract

Phthalocyanines and subphthalocyanines have emerged as highly adaptable molecular platforms with diverse applications, predominantly due to their tunable photophysical properties achieved through the variation in axial and peripheral substituents and central metal atoms. Despite these benefits, their broader application has been hindered by their intrinsic hydrophobicity and strong aggregation in aqueous environments, leading to aggregation-caused quenching (ACQ) and poor photoluminescence performance. Recent advances have demonstrated that integrating aggregation-induced emission luminogens (AIEgens), such as tetraphenylethene and triphenylamine, into phthalocyanine and subphthalocyanine frameworks can efficiently overcome ACQ. This strategy restricts intramolecular motions, converting traditional ACQ-type systems into AIE-active materials with significantly improved emission. Moreover, the unique cone-shaped, π-conjugated architecture of subphthalocyanines enables efficient fluorescence resonance energy transfer when combined with AIE-active groups, further enhancing their photophysical properties. In this perspective, we highlight the recent progress in the development of AIEgen-integrated phthalocyanines and subphthalocyanines, discuss their structure–activity relationships, and explore their potential for advanced applications. To our knowledge, this is the first review to focus on the growing importance and future opportunities of integrating AIEgens with phthalocyanine and subphthalocyanine systems.

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Govardhana Babu Bodedla

Dr Govardhana Babu Bodedla obtained his BSc and MSc degrees from Acharya Nagarjuna University (ANU) in 2008 and 2010, respectively, and a PhD from the Indian Institute of Technology Roorkee (IITR), India, in 2016. He worked as a postdoctoral researcher at Hong Kong Baptist University (from 2017 to 2020) and at The Hong Kong Polytechnic University (from 2020 to 2023). Since 2023, he has been working as a Research Assistant Professor at the Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University. His current research interests focus mainly on the rational design and synthesis of tetrapyrrolic macrocycle-based materials for photocatalytic and electrocatalytic applications.

Shengyi Ke

Shengyi Ke has been pursuing his undergraduate degree at the Hong Kong Polytechnic University (PolyU) since 2022. During his undergraduate studies, he became a research assistant through PolyU Undergraduate Research and Innovation Scheme (URIS). His research interests are centered on the development of advanced organometallic/organic polymeric materials for photothermal and photoelectrical applications.

Yibing Cao

Yibing Cao entered the Department of Applied Biology and Chemical Technology at The Hong Kong Polytechnic University in 2022 as an undergraduate student. Her research interests focus on organic and organometallic materials for photocatalysis and electrocatalysis.

Lijie Zhang

Lijie Zhang graduated from Changchun University of Science and Technology with a bachelor's and master's degrees, and his PhD is from the University of Chinese Academy of Sciences. He is now a Professor in the College of Chemistry and Material Science in Wenzhou University. His main research focus is on the controlled growth and optoelectronic application of low-dimensional semiconductor materials. Currently, he has published over 130 papers in journals such as Nat. Nanotechnol., Nat. Commun., Adv. Funct. Mater., ACS Nano, and Nano Lett., with over 4000 citations in SCI. He has been granted more than 10 invention patents.

Wai-Yeung Wong

Wai-Yeung Wong (Raymond) obtained his BSc (Hons.) and PhD degrees from The University of Hong Kong. After postdoctoral works at Texas A&M University and the University of Cambridge, he joined Hong Kong Baptist University from 1998 to 2016 and he now works at the Hong Kong Polytechnic University as the Dean of Faculty of Science and Chair Professor of Chemical Technology. His research focuses on organometallic and materials chemistry, especially aiming at developing multifunctional molecules and polymers for (opto)electronics and energy science.

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1. Introduction

Over the decades, phthalocyanines and their derivatives, generally considered as the synthetic analogs of porphyrins, have received much interest owing to their ease of structural modification and variety of applications in photovoltaics,^1–7 organic electronics,^8–13 catalysis,^14–21 biomedicine,^22–26 sensors,^27–30 fluorescent probes,^31–33 and environmental remediation.^34–37 The photophysical and electrochemical properties of phthalocyanines can be easily fine-tuned through molecular engineering, including variations in the central metal atom and the integration of various chromophores at the peripheral and axial positions. Among the substituted phthalocyanines, axially substituted silicon (Si(IV))-phthalocyanines have attracted attention as second-generation photosensitizers for photodynamic therapy (PDT) in both cancerous and non-cancerous diseases.³¹ Notably, these axially substituted Si(IV)-phthalocyanines exhibit strong absorption in the red, far-red, and near-infrared (NIR) (Q-band, ca. 650–800 nm) regions, allowing for prominent singlet oxygen (¹O₂) generation and deep tissue penetration upon photoactivation. This leads to the selective impairment of malignant cells with negligible systemic toxicity. Nevertheless, the potential use of most phthalocyanines in catalysis, organic electronics, and biomedicine is restricted due to their low solubility in organic solvents, intrinsic hydrophobicity, and strong tendency to aggregate in aqueous environments. Typically, the aggregation of phthalocyanines leads to quenching of emission, usually referred to as aggregation-caused quenching (ACQ) of photoluminescence. This ACQ gives rise to short-lived photoexcited states, low photoluminescence quantum yield (Φ_PL), and a reduction in the generation of reactive oxygen species (ROS), subsequently resulting in low ¹O₂ quantum yields (Φ_Δ). This limits their efficacy in a wide range of applications. To address these challenges, several strategies have been attempted, such as introduction of polar substituents including sulfonate,^38,39 pyridinium,⁴⁰ quaternary ammonium,^41–46 carboxylate,^47–50 imidazolyl,^51,52 and various phenolic groups at the axial or peripheral positions of phthalocyanines.^53–55 Although these modifications help increase the solubility and enhance the optoelectronic properties of phthalocyanines, they do not completely resolve the problem of ACQ.

On the other hand, subphthalocyanines, which are the lowest homologs of phthalocyanines, possess an electron-rich nature and a noncentrosymmetric C_3v cone-shaped structure, and exhibit strong absorption and emission in the visible region.⁵⁶ This makes them attractive for various applications, including organic semiconductors,^57,58 solar cells,^59–61 nonlinear optical materials,^62–64 and fluorescent probes.^65–68 Because of their exceptional structure, they have also been used for asymmetric phthalocyanine synthesis and catalytic degradation.^69–71 However, similar to phthalocyanines, subphthalocyanines frequently exhibit ACQ upon aggregation, which restricts their use in the aforementioned applications.

An alternative and efficient approach to overcoming ACQ is the integration of aggregation-induced emission (AIE) luminogens (AIEgens) into the frameworks of phthalocyanines and subphthalocyanines. Certain molecules exhibit enhanced emission upon aggregation and in the solid state, a phenomenon known as AIE, due to the presence of AIEgens in their molecular structure.^72,73 This is in contrast to conventional fluorophores. The AIE effect is mainly attributed to the restriction of intramolecular rotations and vibrations in the aggregated or solid state, which hampers non-radiative decay pathways and leads to intensified emission. This ultimately provides long-lived photoexcited state electron lifetime (τ_PL) values, thereby enhancing Φ_PL and ROS generation for AIEgen-conjugated molecules. The most typical AIEgens, namely tetraphenylethene (TPE),^59,74 triphenylamine (TPA),⁷⁵ and phthalonitrile derivatives^76,77 (Fig. 1), have been effectively introduced into the frameworks of phthalocyanines and subphthalocyanines. This strategy is particularly beneficial for transforming such large π-conjugated and planar molecules from ACQ-type to AIE-type upon aggregation. Since AIE was first discovered by Tang and co-workers in 2001,⁷⁸ AIE-active molecules have been employed in many applications, including the biomedical field, such as imaging-guided PDT, targeted chemotherapy, long-term mitochondrial tracking, and enzyme-activated diagnostic probes,^79–82 as well as in catalysis,^73,83 OLED devices,^84–86 and sensor applications.^87–89 After a careful literature survey, we found that very few papers have been published on AIEgen-integrated phthalocyanines and subphthalocyanines, and their applications remain limited. Thus, herein, we have summarized the phthalocyanines and subphthalocyanines reported in the literature so far and discussed their AIE properties, with the aim of developing promising phthalocyanines and subphthalocyanines with AIE characteristics for a wide range of future applications.

Fig. 1 Pictorial representation of AIEgens attached at different positions of phthalocyanines and subphthalocyanines.

2. Discussion

2.1. AIEgen-conjugated phthalocyanines

The emission properties of phthalocyanines can be fine-tuned by introducing various AIEgens at the axial and peripheral positions of the phthalocyanine core.^90,91 The most commonly used AIEgens are TPE and TPA, and the central metals in phthalocyanines are typically zinc (Zn), copper (Cu), and Si. The chemical structures of AIEgen-conjugated phthalocyanines are shown in Fig. 2, and their related photophysical properties are presented in Table 1.

Fig. 2 Structures of AIEgen-conjugated phthalocyanines and related control phthalocyanines.

Table 1 Photophysical properties of AIEgen-conjugated phthalocyanines and subphthalocyanines

Compound	λ abs (nm)	λ em (nm)	τ PL (ns)	Φ PL	Φ Δ	Ref.
a Absorption peak wavelength. b Emission peak wavelength. c Photoexcited state electron lifetime. d Photoluminescence quantum yield. e ^1O2 quantum yield. f Not applicable.
1	353, 678	678	5.34	0.06	0.043	75
2	357, 681	685	1.56	0.08	0.016	75
3	357, 683	687	8.58	0.48	0.530	75
4	685	675	na^f	0.007	0.09	94
5	695	706	na^f	0.297	0.37	94
6	692	705	na^f	0.004	0.08	94
7	689	700	na^f	0.351	0.21	94
8	677	na^f	na^f	na^f	na^f	76
9	679	439, 694	na^f	na^f	na^f	77
10	680	433, 695	na^f	na^f	na^f	77
11	678	443, 695	na^f	na^f	na^f	77
12	680	445, 695	na^f	na^f	na^f	77
13	681	438, 695	na^f	na^f	na^f	77
14	569	584	na^f	2.20	na^f	74
15	589	615	na^f	13.70	na^f	74
16	568	582	na^f	0.60	na^f	74

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Three Si(IV)-phthalocyanines 1–3 with axially substituted TPA terminal groups and either fluorinated or non-fluorinated bisphenol A (BPA) bridge groups were designed, synthesized, and characterized by Liu et al.⁷⁵ The photophysical properties of these Si(IV)-phthalocyanines mainly depended on the nature of the BPA bridge and the presence of TPA groups. All three Si(IV)-phthalocyanines exhibited dual emission peaks in their emission spectra. The emission peaks in the range of 675–688 nm were attributed to the typical Si(IV)-phthalocyanine core, while the peak at 396 nm was assigned to the TPA moieties. Among the Si(IV)-phthalocyanines, 3, which contains both TPA and fluorinated BPA, exhibited the highest Φ_PL, Φ_Δ, and τ_PL value in tetrahydrofuran (THF) solution. This is attributed to the rigid molecular skeleton of 3, which can hamper ACQ. In particular, Si(IV)-phthalocyanine 1, with only TPA moieties, exhibited a strong AIE phenomenon in THF/water (H₂O) mixtures, owing to the restriction of intramolecular rotation caused by the TPA groups in the solid state (Fig. 3(A)). These results indicate that understanding the relationship between molecular structure and photophysical properties of Si(IV)-phthalocyanines can offer important insights for the rational design of novel phthalocyanines with enhanced AIE characteristics for PDT and related applications.

Fig. 3 (A) Change of fluorescence intensity at 396 nm of 3 in THF/H₂O mixtures (inset shows the fluorescence intensity at 600–800 nm). (B) The self-assembling mechanism of DSPE@3 nanoparticles and their possible mechanism of action in mediating in vitro photodynamic therapy on MCF-7 breast cancer cells. (C) The particle size distribution of DSPE@3 in H₂O (inset is TEM of DSPE@3). (D) Possible trafficking and distribution mechanism of 3@AuNR@SiO₂ in MCF-7 cells. (E) The size distribution profile and (F) TEM image of 3@AuNR@SiO₂. (G) The fluorescence images of (a) AuNR, (b) AuNR@SiO₂, (c) 3, and (d) 3@AuNR@SiO₂ at λ_ex = 365 nm. (H) The phototoxicity of 3@AuNR@SiO₂ against MCF-7 breast cancer cells was studied using the Cell Counting Kit-8 (CCK-8) assay (C_Au = 0, 20, 40, 60, 80, 100 µg mL⁻¹). (I) The fluorescence emission of aggregated 8 in mixed dimethylformamide (DMF)/H₂O solvents with reaction time of 10 h. (J) The solid state fluorescence emission spectra of 8 synthesized after different reaction time. Part (A): Reproduced with permission.⁷⁵ Copyright 2022, Elsevier SD. Parts (B & C): Reproduced with permission.⁹² Copyright 2023, Elsevier SD. Parts (D–H): Reproduced with permission.⁹³ Copyright 2025, Elsevier SD. Parts (I & J): Reproduced with permission.⁷⁶ Copyright 2016, Elsevier SD.

As lysosome-targeting therapy represents a promising approach to overcoming drug resistance in cancer treatment, the development of nanodrugs with efficient lysosomal targeting is very important. Thus, a nanoparticle, DSPE@3, was developed by encapsulating Si(IV)-phthalocyanine 3 in a distearoylphosphatidylethanolamine–polyethylene glycol 2000 (DSPE-PEG2000) matrix (Fig. 3(B)).⁹² DSPE@3 nanoparticles exhibited a spherical morphology, and the hydrodynamic size of the nanoparticles was found to be 90.44 nm (Fig. 3(C)). These nanoparticles demonstrated outstanding cellular uptake and selective accumulation in the lysosomes of Michigan Cancer Foundation-7 (MCF-7) breast cancer cells. Notably, fluorescent probes showed that DSPE@3 displayed two-color fluorescence imaging and produced sustained intracellular ROS under irradiation with an 860 nm femtosecond laser. The production of ROS enabled lysosome-mediated apoptosis by efficiently disrupting lysosomal function and causing cell death. More importantly, DSPE@3 nanoparticles showed robust phototoxicity and negligible dark toxicity, demonstrating both the therapeutic potential and biocompatibility of DSPE@3 nanoparticles. These findings illustrate that DSPE@3 is a promising photosensitizer for lysosome-targeted PDT, highlighting its potential for the treatment of drug-resistant breast cancer. Moreover, further studies are required to explore the clinical applications and efficacy of DSPE@3 nanoparticles in cancer therapy. The same group further developed a nanoprobe, 3@AuNR@SiO₂, by encapsulating compound 3 within mesoporous silica-coated gold nanorods (AuNR@SiO₂) (Fig. 3(D–F)).⁹³ This design aims to enable timely escape from lysosomes, preventing premature degradation in acidic cellular environments. It has been found that 3@AuNR@SiO₂ displays strong AIE two-photon fluorescence when encapsulated in AuNR@SiO₂ (Fig. 3(G)), enabling real-time tracking in breast cancer cells (Fig. 3(H)), which is lacking in polymer nanocarriers. The nanoprobe 3@AuNR@SiO₂ freely escapes from lysosomes and selectively targets at mitochondria under irradiation. Additionally, it generates substantial ROS and triggers hyperthermia, establishing potent PDT and photothermal therapy effects. Tumor cell death was confirmed by flow cytometry, which demonstrated both necrosis and apoptosis. These results demonstrate that 3@AuNR@SiO₂ acts as a multifunctional probe for lysosome escape, mitochondria targeting, and two-photon fluorescence imaging-guided synergistic cancer therapy. This offers an encouraging approach for breast cancer treatment.

Openda et al. developed three Si(IV)-phthalocyanine derivatives, 4–6 containing TPE units at peripheral and/or axial positions to examine the effect of molecular engineering on their photophysical and AIE properties.⁹⁴ The photophysical and AIE properties of compounds 4–6 were carefully investigated and compared to those of the control Si(IV)-phthalocyanine 7. Diminished photoluminescence and generation of ¹O₂ were observed for Si(IV)-phthalocyanine 4, but it exhibited AIE in the NIR region (700–900 nm) upon aggregation in aqueous environments. In contrast, under the same aqueous conditions, Si(IV)-phthalocyanine 5, which possesses four peripheral TPE units, did not exhibit AIE behaviour but displayed enhanced Φ_PL and ¹O₂ generation. On the other hand, Si(IV)-phthalocyanine 6, with both axial and peripheral TPE units, showed reduced photoluminescence, lower ¹O₂ generation, and no AIE. These results are completely different from those observed for Si(IV)-phthalocyanines 4 and 5. This reveals the essential role of the substitution patterns of TPE units in fine-tuning the photodynamic and AIE properties of Si(IV)-phthalocyanines. The ability to control AIE behaviour via molecular engineering suggests that TPE-functionalized Si(IV)-phthalocyanines are promising candidates for applications in biomedical fields and image-guided phototherapy. The balance between AIE and ¹O₂ generation could further enhance their therapeutic efficacy and extend their potential use in PDT.

Generally, Cu(II)-phthalocyanines are mostly non-fluorescent owing to the fast energy transfer from the first singlet excited state (S₁) to the triplet state (T₁) through open-shell paramagnetic Cu(II) mediated spin–orbit interaction.⁷⁶ Thus, to achieve emission from Cu(II)-phthalocyanines, a dendritic Cu(II)-phthalocyanine 8 was facilely synthesized through a cycloaddition reaction between a biphenyl phthalonitrile precursor and Cu(II) ions. This dendritic Cu(II)-phthalocyanine exhibited excellent solubility in polar aprotic solvents but no emission in solution. Notably, Cu(II)-phthalocyanine 8 showed strong blue fluorescence at around 480 nm and pronounced AIE in the solid state and upon aggregation (Fig. 3(I)). This is attributed to the restriction of intramolecular rotation in the aggregated state, a typical AIE phenomenon. Moreover, when 8 was synthesized with extended reaction times, it displayed enhanced and blue-shifted solid state blue fluorescence with greater thermal stability, ascribed to enhanced crystallinity (Fig. 3(J)). These results indicate the significance of reaction conditions in modulating the molecular geometry, crystallinity, and photophysical properties of dendritic Cu(II)-phthalocyanine 8. Because of its easy synthesis, tunable blue emission, and robust thermal stability, dendritic Cu(II)-phthalocyanine 8 can be employed as a valuable candidate for advanced optoelectronic devices and full-color display technologies. In continuation of the above work, the same group further synthesized a family of dendritic Zn(II)-phthalocyanines, 9–13 substituted with hydroquinone, naphthalenediol, dihydroxybiphenyl, bisphenol F, and BPA moieties through a two-step reaction using donor–linker–acceptor (D–π–A)-type bisphthalonitrile precursors and Zn(II) ions.⁷⁷ The photophysical properties of these dendritic Zn(II)-phthalocyanines were systematically studied in solution, mixed solvents, solid state, and as polymethyl methacrylate (PMMA) composite films. They exhibited both molecular NIR photoluminescence and AIE characteristics. Particularly, dendritic Zn(II)-phthalocyanines, 9–11 containing hydroquinone, naphthalenediol, or dihydroxybiphenyl moieties exhibited an outstanding conversion from strong NIR emission in the molecular state to intense blue fluorescence in the solid state and upon aggregation. In contrast, Zn(II)-phthalocyanines with bisphenol F and BPA moieties exhibited only NIR emission in the molecular state and no emission upon aggregation or in the solid state, signifying typical ACQ behavior. Density functional theory (DFT) calculations further supported the relationship between molecular structure and the observed luminescence properties through electron density distribution. Additionally, dendritic Zn(II)-phthalocyanines displayed well-organized three-dimensional microspheres and two-dimensional leaf-like microstructures upon aggregation in aqueous mixtures. Moreover, the dendritic Zn(II)-phthalocyanines not only exhibited strong emission in the solid state but also when embedded in PMMA films. These results signify that dendritic Zn(II)-phthalocyanines, 9–11 can be used as multipurpose fluorophores for high-performance biological imaging, fluorescent flexible optoelectronic devices, and chemosensors due to their tunable emission, solid state fluorescence, and easy processability.

Overall, these findings highlight that precise molecular engineering of phthalocyanines permits fine-tuning of their AIE properties, which is vital for developing top-notch materials for biomedical and optoelectronic applications. In particular, certain Si(IV)-phthalocyanines with TPE moieties and DSPE@3 exhibit high efficacy for lysosome-targeted PDT, especially against drug-resistant cancers and in image-guided phototherapy. Furthermore, dendritic Zn(II)- and Cu(II)-phthalocyanines display variable solid state fluorescence, making them promising candidates for outstanding imaging, chemosensors, and optoelectronic devices. Lastly, understanding the structure–property relationships is crucial for the development of next-generation, exceptional, and functional phthalocyanine-based materials.

2.2. AIEgen-conjugated subphthalocyanines

In general, subphthalocyanines exhibit distinctive photophysical properties due to their unique aromatic structures and geometric characteristics. To enhance emission intensity, several AIEgen-conjugated subphthalocyanines have been developed by introducing TPE moieties at the axial and peripheral positions of the subphthalocyanine core. The resulting AIEgen-conjugated subphthalocyanines are shown in Fig. 4, and their corresponding photophysical properties are presented in Table 1.

Fig. 4 Structures of AIEgen-conjugated subphthalocyanines and related control subphthalocyanines.

Dinag et al. synthesized two subphthalocyanines, 15 and 16, containing axially and peripherally substituted TPE moieties, and investigated their AIE properties under various conditions.⁷⁴ In THF solution, subphthalocyanine 15, with peripherally substituted TPE moieties, exhibited a higher Φ_PL than subphthalocyanine 16, which contained axially modified TPE moieties. In these subphthalocyanines, the TPE moiety acts as an energy donor, while the subphthalocyanine core acts as an energy acceptor. A fluorescence resonance energy transfer (FRET) phenomenon is possible in both 15 and 16 due to the overlap between the emission spectrum of the TPE moiety and the absorption spectrum of the control subphthalocyanine 14, which lacks TPE (Fig. 5(A)). Notably, compound 16 exhibited both FRET and ACQ phenomena when excited at 480 nm, corresponding to the subphthalocyanine absorption, and a significant AIE was observed upon excitation at 270 nm, which is related to the TPE unit (Fig. 5(B)). Under the same conditions, in contrast, compound 15 did not show AIE properties, although it exhibited a higher Φ_PL than 16. These findings illustrate the different effects of axial versus peripheral functionalization on the photophysical properties of subphthalocyanines. This is beneficial for designing promising fluorescent probes and sensing materials using axially modified subphthalocyanines.

Fig. 5 (A) (a) The spectral overlap of the normalized fluorescence spectrum of hydroxy TPE (red line) in the aggregate state and the excitation spectrum of subphthalocyanine 14 in THF (black line) and (b) the schematic diagram of FRET process in 16. (B) The emission spectra of 16 recorded in different ratios of THF/H₂O mixtures under (a) 270 nm and (b) 480 nm excitation. Parts (A & B): Reproduced with permission.⁷⁴ Copyright 2021, Elsevier SD.

In another report, phthalonitriles with different TPE substitution positions were first synthesized and subsequently used as precursors to develop a series of axially and peripherally TPE-integrated subphthalocyanines, 17–20.⁵⁹ The crystallographic structures of the phthalonitriles revealed that the bulky TPE moieties suppressed intermolecular π–π interactions in the solid state. AIE studies showed that the precursor phthalonitriles exhibited excellent AIE properties, as evidenced by enhanced emission intensity with increasing H₂O content in THF/H₂O mixtures. In contrast, all the TPE-substituted subphthalocyanines, 17–20, showed quenched emission with increasing H₂O content in THF/H₂O mixtures, indicating that the ACQ phenomenon dominates in these subphthalocyanines. These results demonstrate that although bulky TPE groups were introduced parallel and perpendicular to the π-plane of subphthalocyanines, strong aggregation of the π-plane is not favored. Moreover, DFT calculations revealed that the lack of AIE properties in these subphthalocyanines is due to strong intramolecular interactions between the subphthalocyanine macrocycle and the TPE groups. This leads to a significant intramolecular charge transfer contribution, which is close to the Q-band. Another reason is that the fixation of TPE groups around the subphthalocyanine macrocycle makes it difficult to adopt a favorable conformation for AIE properties in the aggregated state. These results highlight that the development of novel AIEgens is required to enable subphthalocyanines to overcome ACQ and exhibit AIE.

Altogether, these findings illustrate that the position and mode of TPE integration significantly affect the photophysical properties of subphthalocyanines. Although some subphthalocyanines promote AIE, others still suffer from ACQ, highlighting the urgent need for further molecular design to fully understand and develop AIE-active subphthalocyanines for advanced applications

3. Conclusions and outlook

In summary, recent advances in the design, synthesis, and functionalization of phthalocyanines and subphthalocyanines that exhibit AIE have unlocked new paths for both fundamental research and practical applications. Traditional limitations, such as poor solubility, ACQ, and limited photophysical tunability in phthalocyanines and subphthalocyanines, have been effectively addressed through systematic molecular engineering, including the introduction of dendritic architectures and AIE-active moieties such as TPE and TPA. Notable accomplishments in this field include the development of dendritic Cu(II)- and Zn(II)-phthalocyanines with tunable emission and enhanced solid state fluorescence, as well as AIE-active Si(IV)-phthalocyanines with improved photosensitizing properties for PDT. The successful preparation of biocompatible nanoparticles using AIE-active Si(IV)-phthalocyanines through encapsulation has enabled effective lysosomal targeting, two-color imaging, and potent photodynamic effects. These findings highlight their potential as multifunctional nanomedicines for image-guided cancer therapy. Moreover, strategic studies on the positional effects of AIE-active moieties have provided important insights into the structure–property relationships of phthalocyanines and subphthalocyanines, influencing photoluminescence, ¹O₂ generation, and AIE/ACQ characteristics.

However, several challenges and opportunities still remain. Attaining an ideal balance among AIE, Φ_PL, and ¹O₂ is a key factor for biomedical and display applications. The development and introduction of diverse AIE-active scaffolds into phthalocyanine and subphthalocyanine frameworks could lead to innovative materials with unique properties and broader utility. The expansion of cutting-edge nanoplatforms for targeted delivery and real-time monitoring, as well as a deeper understanding of AIE and related phenomena, will further drive innovation. Apart from PDT and imaging, these materials can also serve as potential candidates for applications in organic electronics, artificial photosynthesis, sensing, and environmental remediation.

Author contributions

G. B. Bodedla proposed the concept and wrote the original manuscript. S. Ke and Y. Cao were involved in the manuscript write-up. L. Zhang and W.-Y. Wong supervised and revised the manuscript. All authors discussed the results and evaluated the manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

No primary research results, software or code have been included and no new data were generated or analysed as part of this review.

Acknowledgements

G. B. B. acknowledges the financial support from the Start-up Fund for Research Assistant Professors (RAPs) under the Strategic Hiring Scheme (P0048725) of the Hong Kong Polytechnic University. W.-Y. W. is grateful to the financial support from the RGC Senior Research Fellowship Scheme (SRFS2021-5S01), the Hong Kong Research Grants Council (PolyU 15301922), Research Institute for Smart Energy (CDAQ), Research Centre for Nanoscience and Nanotechnology (CE2H), and Miss Clarea Au for the Endowed Professorship in Energy (847S).

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