Fluorescence Up-Conversion Studies of [2,2′-Bipyridyl]-3,3′-diol in Octyl-β‑d‑glucoside and Other Micellar Aggregates

In this present work, excited state double proton transfer dynamics (ESIDPT) of 2,2′-bipyridyl-3,3′-diol (BP­(OH)₂) molecules has been probed in a nontoxic, biocompatible sugar surfactant assembly, namely, octyl-β-d-glucoside (OBG) micelle with the help of steady state and fluorescence up-conversion techniques. Moreover, the ultrafast double proton transfer dynamics in conventional micelles (SDS, CTAB) and bile salts aggregates have been probed and compared. Interestingly, in all these supramolecular aggregates, the ESIDPT dynamics is found to follow sequential pathway; however, the time-scale of proton transfer dynamics varies from 11 to 30 ps. This difference in proton transfer time scale in different supramolecular aggregates has been explained in terms of accessibility of water molecules in the vicinity of probe

Topological Influence of Lyotropic Liquid Crystalline Systems on Excited-State Proton Transfer Dynamics

In the present work, we have investigated the excited-state proton transfer (ESPT) dynamics inside lipid-based reverse hexagonal (H_II), gyroid Ia3d, and diamond Pn3m LLC phases. Polarized light microscopy (PLM) and small-angle X-ray scattering (SAXS) techniques have been employed for the characterization of LLC systems. Time-resolved fluorescence results reveal the retarded ESPT dynamics inside liquid crystalline systems compared to bulk water, and it follows the order H_II < Ia3d < Pn3m < H₂O. The slower solvation, hampered “Grotthuss” proton transfer process, and most importantly, topological influence, of the LLC systems are believed to be mainly responsible for the slower and different extent of ESPT dynamics. Interestingly, recombination dynamics is found to be faster with respect to bulk water and it follows the order H₂O < Pn3m < Ia3d < H_II. Faster recombination dynamics arises due to lower dielectric constant and different channel diameters of these LLC systems. However, the dissociation dynamics is found to be slower than bulk water and it follows the order H_II < Ia3d < Pn3m < H₂O. Differences in critical packing parameter of LLC systems are believed to be the governing factors for the slower dissociation dynamics in these liquid crystalline systems

Ultrafast Fluorescence Dynamics of Highly Stable Copper Nanoclusters Synthesized inside the Aqueous Nanopool of Reverse Micelles

Herein, we have reported a new strategy for the synthesis of highly stable fluorescent copper nanoclusters (CuNCs) with l-cysteine (Cys) as a protecting ligand within the water nanopool of reverse micelles (RMs). In the present work, efforts are also given to address the origin of excitation-dependent fluorescence spectral shift of CuNCs. From our experiments, we have elucidated that the broad fluorescence from CuNCs in RMs consists of two spectrally overlapped bands corresponding to the metal-core and surface states of CuNCs. The intrinsic emission of CuNCs distributed in shorter wavelength regions (<470 nm) is mainly originated from the metal core. On the other hand, the extrinsic fluorescence band (>470 nm) is caused by surface states and consists of a much broader emission because of the presence of numerous surface states. The trapping of excited electrons in the various surface states leads to the emission in the longer wavelength regions and is believed to be responsible for excitation-dependent emission of CuNCs in RMs. Excited state dynamics, which controls the optical properties of CuNCs, have also been investigated by time-correlated single photon counting (TCSPC) and femtosecond fluorescence upconversion techniques. Femtosecond fluorescence upconversion and TCPSC decay profiles of CuNCs comprise of multitude of lifetime components spanning from <1 ps to few nanosecond timescales. We have rationalized the dynamics on the basis of several competing deactivation pathways and a broad distribution of radiative electron–hole recombination dynamics originating from core and surface states