We report the synthesis of a new class of photoresponsive C₆₀–DCE–diphenylaminofluorene nanostructures and their intramolecular photoinduced energy and electron transfer phenomena. Structural modification was made by chemical conversion of the keto group in C₆₀(>DPAF-C_n ) to a stronger electron-withdrawing 1,1-dicyanoethylenyl (DCE) unit leading to C₆₀(>CPAF-C_n ) with an increased electronic polarization of the molecule. The modification also led to a large bathochromic shift of the major band in visible spectrum giving measureable absorption up to 600 nm and extended the photoresponsive capability of C₆₀–DCE–DPAF nanostructures to longer red wavelengths than C₆₀(>DPAF-C_n ). Accordingly, C₆₀(>CPAF-C_n ) may allow 2γ-PDT using a light wavelength of 1000–1200 nm for enhanced tissue penetration depth. Production efficiency of singlet oxygen by closely related C₆₀(>DPAF-C_2M) was found to be comparable with that of tetraphenylporphyrin photosensitizer. Remarkably, the ¹O₂ quantum yield of C₆₀(>CPAF-C_2M) was found to be nearly 6-fold higher than that of C₆₀(>DPAF-C_2M), demonstrating the large light-harvesting enhancement of the CPAF-C_2M moiety and leading to more efficient triplet state generation of the C₆₀> cage moiety. This led to highly effective killing of HeLa cells by C₆₀(>CPAF-C_2M) via photodynamic therapy (200 J cm⁻² white light). We interpret the phenomena in terms of the contributions by the extended π-conjugation and stronger electron-withdrawing capability associated with the 1,1-dicyanoethylenyl group compared to that of the keto group.

The first, highly two-photon active C₆₀ derivative comprised of a A-sp³-D conjugate structure was synthesized showing effective two-photon absorption cross-sections (σ₂′ = 196 ×10⁻⁴⁸ cm⁴ sec⁻¹ molecule⁻¹⁾ in the nanosecond regime among the best values for diphenylaminofluorene-based AFX chromophores.

It is known that multiple cationic charges are required to produce broad-spectrum antimicrobial photosensitizers (PS) for photodynamic inactivation (aPDI) or photodynamic therapy of bacteria and fungi. In the present study we describe the synthesis and aPDI testing of a set of derivatives prepared from the parent pheophytin molecule with different numbers of attached side arms (1–3) each consisting of five quaternized cationic groups (pentacationic), producing the corresponding [Zn²⁺]pheophorbide-a-N(C₂N⁺C₁C₃)₅ (Zn-Phe-N₅ ⁺, 5 charges), [Zn²⁺]chlorin e₆-[N(C₂N⁺C₁C₃)₅]₂ (Zn-Chl-N₁₀ ⁺, 10 charges) and [Zn²⁺]mesochlorin e₆-[N(C₂N⁺C₁C₃)₅]₃ (Zn-mChl-N₁₅ ⁺, 15 charges). Moreover, a conjugate between Zn-Phe-N₅ ⁺ and the antibiotic vancomycin called Van-[Zn²⁺]-m-pheophorbide-N(C₂N⁺C₁C₃)₅ (Van-Zn-mPhe-N₅ ⁺) was also prepared. The aPDI activities of all compounds were based on Type-II photochemistry (¹O₂ generation). We tested these compounds against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA), Gram-negative Escherichia coli, and the fungal yeast Candida albicans. All three compounds were highly active against MRSA, giving eradication (≥6 logs of killing) with <1.0 μM and 10 J cm⁻² of 415 nm light. The order of activity was Zn-Phe-N₅ ⁺ > Zn-Chl-N₁₀ ⁺ > Zn-mChl-N₁₅ ⁺. In the case of E coli the activity was much lower (eradication was only possible with 50 μM Zn-mChl-N₁₅ ⁺ and 20 J cm⁻²). The order of activity was the reverse of that found with MRSA (Zn-mChl-N₁₅ ⁺ > Zn-Chl-N₁₀ ⁺ > Zn-Phe-N₅ ⁺). Activity against C. albicans was similar to E. coli with Zn-mChl-N₁₅ ⁺ giving eradication. The activity of Van-Zn-mPhe-N₅ ⁺ was generally lower than that of Zn-Phe-N₅ ⁺ (except for E. coli). Red (660 nm) light was also effective as might be expected from the absorption spectra. An initial finding that Van-Zn-mPhe-N₅ ⁺ might have higher activity against vancomycin resistant Enterococcus fecium (VRE) strains (compared to vancomycin sensitive strains) was disproved when it was found that VRE strains were also more sensitive to aPDI with Zn-Phe-N₅ ⁺. The minimum inhibitory concentrations of Van-Zn-mPhe-N₅ ⁺ were higher than those of Van alone, showing that the antibiotic properties of the Van moiety were lessened in the conjugate. In conclusion, Zn-Phe-N₅ ⁺ is a highly active PS against Gram-positive species and deserves further testing. Increasing the number of cationic charges increased aPDI efficacy on C. albicans and Gram-negative E. coli.

Direct detection of singlet oxygen (¹O₂) production under irradiation of molecular micelle-like hexa(sulfo-n-butyl)[60]fullerene (FC₄S) self-assembled nanospheres at 500–600 nm was obtained by the measurement of its near-infrared luminescence at 1270 nm. This photocatalytic effect makes FC₄S a potential alternative sensitizer to TiO₂ and feasible for use in the visible region in addition to its intrinsic high UV efficiency. Despite having a relatively low optical absorption of FC₄S at 600 nm, appreciable ¹O₂ signal was detected comparable to that of hematoporphyrin derivatives Photofrin at the same molar concentration, but less than sulfonated aluminium phthalocyanine, AlS₄Pc. The quantum yield of FC₄S for the generation of ¹O₂ in H₂O was roughly estimated to be 0.36 using the relative correlation to that of C₆₀/γ-CD. The absolute value is not available. These results demonstrated efficient triplet energy transfer from ³FC₄S* to molecular oxygen in the nanosphere structure. We also confirmed certain retention between photocatalytic characteristics of underivatized C₆₀ with that of FC₄S, a C₆₀ hexaadduct containing a single covalent bond between each addend and the fullerene cage, in contrast to other Bingel-type hexamalonate adducts of C₆₀ in the literature with a low ¹O₂ yield.