Femto- to micro-second photobehavior of photosensitizer drug trapped within a cyclodextrin dimer

• Published in: Photochemical & photobiological sciences 2013-12, Vol.12 (12), p.2119-2129
• Main Authors: Wang, Yilun, Cohen, Boiko, Aykaç, Ahmet, Vargas-Berenguel, Antonio, Douhal, Abderrazzak
• Format: Article
• Language: English
• Subjects: beta-Cyclodextrins - chemistry; Biochemistry; Biomaterials; Chemistry; Dimerization; Hydrogen-Ion Concentration; Light; Photolysis; Photosensitizing Agents - chemistry; Physical Chemistry; Plant Sciences; Porphyrins - chemistry; Quantum Theory; Singlet Oxygen - chemistry; Spectrophotometry, Ultraviolet; Time Factors; Water - chemistry
• ISSN: 1474-905X; 1474-9092
• DOI: 10.1039/c3pp50179e

The interactions of 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (TSPP, a singlet oxygen photosensitiser molecule) with a hexa-2,4-diynediyl bridged β-cyclodextrin dimer (CD-CD) in aqueous solutions of pH 7 were studied using steady-state UV-visible absorption/emission and femto- to millisecond time-resolved spectroscopy. TSPP forms 1:1 complexes with CD-CD ( K e = 1.9 × 10 8 M −1 at 293 K). The value of K e indicates a high affinity of TSPP to form complexes with CD-CD. The chemical nano-cavity has a notable effect on the fluorescence lifetimes of the Q x state (9.3 ns in water and 10.8 ns in CD-CD). The rotational times (410 ps for TSPP in water and 0.03 ns (12%) and 1.1 ns (88%) for the TSPP:CD-CD complexes) indicate the robustness of the formed entities, and fast depolarization of emission, most probably involving the porphyrin skeleton and phenyl ring motions. The ultrafast femtosecond component (60-100 fs) of TSPP is moderately affected by the confining environment, which instead strongly influences the ps component (1-2 ps in water and 5 ps within CD-CD) assigned to the vibrational relaxation of the Q x state. Moreover, a 50 ps component emerges in the emission transients in the 640-720 nm range, and which is assigned to a thermalization of the hot Q x state. The effect of O 2 on the triplet state of the encapsulated TSPP was also studied and discussed in light of the shielding effect of the CD-CD cavity. We observed comparable quantum yield (0.62 and 0.69) of the generated singlet molecular oxygen of TSPP without and with CD-CD. We believe that our results on the molecular interaction between TSPP and CD-CD from femtosecond to millisecond regime at both ground and electronically first excited states give relevant information for improving our understanding of this kind of caged drugs, and thus for a better design of drug:nanocarrier complexes. A particular implication for the use of CD-CD as a drug carrier is the high affinity of this host for complex formation with TSPP, while the yield of singlet oxygen generation is still high.respectively.