Dipankar Sukul

Solvation dynamics of DCM in micelles

The solvation dynamics of 4-(dicyanomethylene)-2-methyl-6(p-dimethylaminostyryl) 4H-pyran (DCM) have been studied in neutral (Triton X-100, TX), cationic (cetyl trimethyl ammonium bromide, CTAB) and anionic (sodium dodecyl sulfate, SDS) micelles using picosecond time-resolved Stokes shift. Above the critical micellar concentration for all three micelles, DCM exhibits wavelength-dependent fluorescence decays. At short wavelengths, a fast decay is observed while, at long wavelengths, a distinct growth precedes the decay. The time-dependent Stokes shift indicates that the water molecules in the Stern layer of the micelles relax on a timescale which is markedly slower than the sub-picosecond relaxation dynamics in pure water.

Photoinduced electron transfer between dimethylaniline and oxazine 1 in micelles

Abstract Photoinduced electron transfer (PET) from N , N -dimethylaniline (DMA) to oxazine 1 (OX-1) is studied in micelles. It is observed that in anionic (sodium dodecyl sulfate, SDS) and neutral (Triton X-100, TX) micelles the rate of electron transfer (ET) from DMA to OX-1 is respectively 6.5 and 3 times smaller than that in water, and respectively 162 and 90 times smaller than that in neat DMA. The lower ET quenching constant in micellar media is ascribed to the greater donor–acceptor distance in the micelles.

Solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in a microemulsion

Abstract The photophysical process of the laser dye 4-(dicyanomethylene)-2-methyl-6-( p -dimethylaminostyryl)-4H-pyran (DCM) is studied in aerosol-OT (AOT) microemulsions in n -heptane using picosecond spectroscopy. When AOT and water are added to a solution of DCM in n -heptane, some of the DCM molecules migrate from bulk n -heptane to the water pool. The absorption and emission peaks of the DCM molecules in the polar water pool are markedly red shifted from those in the bulk n -heptane and the emission intensity in the water pool is nearly 40 times higher. Dual emission is not observed in the microemulsions. DCM exhibits slow solvation dynamics in the water pool with an average solvation time of 1.23 ns.

Solvation Dynamics of DCM in Dipalmitoyl Phosphatidylcholine Lipid

Solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran (DCM) in dipalmitoylphosphatidylcholine (DPPC) vesicles in water is studied using picosecond emission spectroscopy. The solvation dynamics of DCM in DPPC vesicles is found to be bi-exponential with two components of 120±20 ps (20%) and 5.5±0.5 ns (80%). This indicates slow relaxation of the water molecules inside the water pool of the lipid vesicles.

Solvation dynamics of 4-aminophthalimide in a polymer (PVP)–surfactant (SDS) aggregate

Solvation dynamics of 4-aminophthalimide (4-AP) in a polymer–surfactant aggregate comprising poly(vinylpyrrolidone) (PVP) and sodium dodecyl sulfate (SDS) is reported. In an aqueous solution even at a polymer concentration much higher than the cross over value (C*), a significant portion (30%) of 4-AP molecules do not bind to PVP. In the presence of a surfactant, SDS, 4-AP binds to the PVP–SDS aggregate completely at a polymer concentration greater than C*. The critical aggregation concentration (c.a.c.) of SDS for PVP is found to be 2 mM. The solvation dynamics of 4-AP in a PVP–SDS aggregate is observed to be slower compared to that in bulk water or in SDS micelles. The slow solvation dynamics is attributed to restrictions imposed on the water molecules squeezed between the polymer chain and micellar aggregates.

Photoisomerization of merocyanine 540 in polymer-surfactant aggregate

Photoisomerization of merocyanine 540 (MC540) in a polymer-surfactant aggregate is studied using picosecond time resolved emission spectroscopy. The aggregate consists of the polymer, poly(vinylpyrrolidone) (PVP) and the surfactant, sodium dodecyl sulphate (SDS). With increase in the concentration of SDS in an aqueous solution of MC540 containing PVP, the emission quantum yield and lifetime of MC540 increase markedly. This indicates marked retardation in the nonradiative photoisomerization process of MC540, when it binds to the polymer-surfactant aggregate. The critical association concentration of SDS for binding to PVP has been found to be 0.5 mM. This is about 16 times lower than the CMC of SDS in pure water (8 mM).

Isomerization and fluorescence depolarization of merocyanine 540 in polyacrylic acid. Effect ofpH

Dynamics of isomerization and fluorescence depolarization of merocyanine 540 (MC540) in an aqueous solution of polyacrylic acid (PAA) have been studied using picosecond time resolved fluorescence spectroscopy. It is observed that the dynamics of isomerization and depolarization are sensitive enough to monitor the uncoiling of PAA at high pH (> 6). At low pH (< 3), when the polymer remains in a hypercoiled form, polymer bound MC540 experiences very high microscopic friction and, hence, the isomerization and depolarization processes are very slow. At high pH (> 6) a polyanion is formed and the polymer assumes an extended configuration due to electrostatic repulsion. At high pH (> 6), the anionic probe MC540 is expelled from the polyanion to bulk water and the dynamics of isomerization and fluorescence depolarization become faster by 12 and 5 times respectively, compared to those at low pH.