Synergy of Electrostatic and π-π Interactions in the Realization of Nanoscale Artificial Photosynthetic Model Systems

Excimer Formation Driven by Excited-State Structural Relaxation in a Covalent Aminonaphthalimide Dimer

Strongly coupled excimer formation from interchromophoric charge transfer driven by the ultrafast excited-state structural dynamics of a 5,5'-linked 4-amino-1,8-naphthalimide covalent homodimer was investigated by ultrafast transient spectroscopy and chemical calculations. Theoretical calculations indicate that the structural relaxation associated with the dihedral motion leads to significantly enhanced interchromophoric charge transfer (CT) coupling, which favors the formation of an excimer-like symmetry-broken CT state. The formation and relaxation dynamics of the excimer state in the dimer are identified via ultrafast transient absorption and fluorescence spectroscopy. The structural relaxation following the photoexcitation occurs in tens of picoseconds and stabilizes the dimer to the strongly coupled excimer state. The highly polar solvents further stabilize the excimer state and enhance the CT character, which enable efficient electron and excitation energy transport in covalent molecular aggregates.

A Greener Route to Blue: Solid-State Synthesis of Phthalocyanines

Phthalocyanines are important organic dyes with a broad applicability in optoelectronics, catalysis, sensing and nanomedicine. Currently, phthalocyanines are synthetized in high boiling organic solvents, like dimethylaminoethanol (DMAE), which is a flammable, corrosive, and bioactive substance, miscible with water and harmful to the environment. Here we show a new solid-state approach for the high-yielding synthesis of phthalocyanines, which reduces up to 100-fold the amount of DMAE. Through systematic screening of solid-state reaction parameters, carried out by ball-milling and aging, we reveal the influence of key variables-temperature, presence of a template, and the amount and role of DMAE in the conversion of tBu phthalonitrile to tetra-tBu phthalocyanine. These results set the foundations to synthesize these high-performance dyes through a greener approach, opening the field of solid-state synthesis to a wider family of phthalocyanines.

A bioinspired hollow g-C3N4-CuPc heterostructure with remarkable SERS enhancement and photosynthesis-mimicking properties for theranostic applications

Surface-enhanced Raman scattering (SERS) based on chemical mechanism (CM) has great potential for superior stability and selectivity. Moreover, a bioinspired CM-Raman substrate-Raman reporter system with charge separation and electron transport nature provides thylakoid-mimicking potential for multifunctional applications. Herein, hollow carbon nitride nanospheres hierarchically assembled with a well-oriented copper(ii) phthalocyanine layer and hyaluronic acid (HCNs@CuPc@HA) were designed as a light-harvesting nanocomposite and photosynthesis-mimicking nanoscaffold that enhance both CM-SERS and photoredox catalysis. Remarkable SERS enhancement was achieved due to the strengthened short-range substrate–molecule interaction, enriched CuPc molecule loading and enhanced light–mater interactions. Meanwhile, the uniform CuPc molecule film mimics a photo-pigment to accelerate the near infrared (NIR)-oxygen generation and photodynamic catalysis of photosynthetic membrane-like HCNs. The experimental findings were further validated by numerical theory analysis. The greatly enhanced SERS signal and photosynthetic-mimicking properties of the heterostructure (denoted as HCNCHs) were successfully employed for circulating tumor cell (CTC) diagnosis and SERS imaging-guided cancer catalytic therapy in tumor xenograft models.

Thylakoid-inspired HCNs@CuPc@HA is designed as a light-harvesting nanocomposite and photosynthesis-mimicking nanoscaffold to simultaneously enhance chemical mechanism-based SERS and photosynthesis-mimicking catalysis for theranostics application.

Exploring the Association of Electron‐Donating Corroles with Phthalocyanines as Electron Acceptors

Electron‐donating corroles (Cor) were integrated with electron‐accepting phthalocyanines (Pc) to afford two different non‐covalent Cor ⋅ Pc systems. At the forefront was the coordination between a 10‐meso‐pyridine Cor and a ZnPc. The complexation was corroborated in a combination of NMR, absorption, and fluorescence assays, and revealed association with binding constants as high as 10⁶  m⁻¹. Steady‐state and time‐resolved spectroscopies evidenced that regardless of exciting Cor or Pc, the charge‐separated state evolved efficiently in both cases, followed by a slow charge‐recombination to reinstate the ground state. The introduction of non‐covalent linkages between Cor and Pc induces sizeable differences in the context of light harvesting and transfer of charges when compared with covalently linked Cor‐Pc conjugates.

A Janus-Type Phthalocyanine for the Assembly of Photoactive DNA Origami Coatings

Design and synthesis of novel photosensitizer architectures is a key step toward new multifunctional molecular materials. Photoactive Janus-type molecules provide interesting building blocks for such systems by presenting two well-defined chemical functionalities that can be utilized orthogonally. Herein a multifunctional phthalocyanine is reported, bearing a bulky and positively charged moiety that hinders their aggregation while providing the ability to adhere on DNA origami nanostructures via reversible electrostatic interactions. On the other hand, triethylene glycol moieties render a water-soluble and chemically inert corona that can stabilize the structures. This approach provides insight into the molecular design and synthesis of Janus-type sensitizers that can be combined with biomolecules, rendering optically active biohybrids.

Peripherally Crowded Cationic Phthalocyanines as Efficient Photosensitizers for Photodynamic Therapy

Photodynamic therapy is a treatment modality of cancer based on the production of cytotoxic species upon the light activation of photosensitizers. Zinc phthalocyanine photosensitizers bearing four or eight bulky 2,6-di(pyridin-3-yl)phenoxy substituents were synthesized, and pyridyl moieties were methylated. The quaternized derivatives did not aggregate at all in water and retained their good photophysical properties. High photodynamic activity of these phthalocyanines was demonstrated on HeLa, MCF-7, and EA.hy926 cells with a very low EC₅₀ of 50 nM (for the MCF-7 cell line) upon light activation while maintaining low toxicity in the dark (TC₅₀ ≈ 600 μM), giving thus good phototherapeutic indexes (TC₅₀/EC₅₀) above 1400. The compounds localized primarily in the lysosomes, leading to their rupture after light activation. This induced an apoptotic cell death pathway with secondary necrosis because of extensive and swift damage to the cells. This work demonstrates the importance of a bulky and rigid arrangement of peripheral substituents in the development of photosensitizers.