Femtosecond to nanosecond dynamics of 2,2′-bipyridine-3,3′-diol inside the nano-cavities of molecular containers

Abstract

Femtosecond fluorescence upconversion measurements are employed to elucidate the mechanism of ultrafast double proton transfer dynamics of BP(OH)2 inside molecular containers (cucurbit[7]uril (CB7) and β-cyclodextrin (β-CD)). Femtosecond up-converted signals of BP(OH)2 in water consist of growth followed by a long decay component (~650 ps). The appearance of the growth component (~35 ps) in the up-converted signal indicates the presence of a two-step sequential proton transfer process of BP(OH)2 in water. Surprisingly, the up-converted signal of BP(OH)2 inside the CB7 nano-cavity does not exhibit any growth component characteristic of a two-step sequential process. Interestingly, the growth component exists inside the nano-cavity of β-CD (having similar cavity size as that of CB7), inferring the presence of a two-step sequential process of PT inside the β-CD nano-cavity. The different features of PT dynamics of BP(OH)2 in the above mentioned two macrocyclic hosts may be attributed to the presence and absence of water solvation network surrounding the BP(OH)2 inside the nano-cavities of β-CD and CB7, respectively. Finally, docking and DFT calculations have been employed in deciphering the molecular pictures of the interactions between BP(OH)2 and the macrocyclic host.

Promoting the “water-wire” mechanism of double proton transfer in [2,2′-bipyridyl]-3,3′-diol by porous gold nanoparticles

“…15 These peaks do not appear in aprotic solvents, nor in hydrophobic pockets. 15,16,23 No appreciable change in the absorption spectrum of BP(OH) 2 was observed in either pure Au, Ag and Au/Ag alloys or the porous NPs (Fig. 2).…”

“…23 BP(OH) 2 is reported to be devoid of any aqueous solvation inside cucurbituril-7, hence promoting concerted DPT, whereas the surrounding water molecules inside b-CD lead to sequential DPT in BP(OH) 2 . 23 Abou-Zied has explained in one of his reports that a special photoinduced tautomerization mechanism takes place in water via a ''water wire'' that connects both of the two hydrogen-bonding centres of the molecule. 16 Proton transfer in this manner is very similar to that explained by the Grotthuss mechanism.…”

Incorporation of Coumarin 6 in cyclodextrins: microcrystals to lamellar composites

“…There are hardly any report on the excited state lifetime of C6 in aqueous environment since this uorophore is insoluble in water. [40][41][42] In the present case, the rise time evokes two possibilities: (i) slow solvation of C6 by water, and (ii) excited state ICT in the probe. Excited C6 decays in about 2.5 ns in pure ethanol or methanol.…”

Ultrafast dynamics of a molecular rotor in chemical and biological nano-cavities

“…23 Briefly, the sample was excited at 420 nm using the second harmonic of a mode-locked Tisapphire laser (Mai-Tai, Spectra Physics). 23 Briefly, the sample was excited at 420 nm using the second harmonic of a mode-locked Tisapphire laser (Mai-Tai, Spectra Physics).…”