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Fluorescence anisotropy measurements and molecular dynamics (MD) simulations have been performed to understand the specific interactions of two structurally similar nondipolar solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), with neat 1-butyl-3-methylimidazolium dicyanamide ([BMIM][N(CN)2]) and also in the presence of glucose. It has been observed that the measured reorientation times of DMDPP in neat [BMIM][N(CN)2] follow the predictions of the Stokes–Einstein–Debye hydrodynamic theory with slip boundary condition. Addition of glucose (0.075 and 0.15 mole fraction) has no bearing on the rotational diffusion of the solute apart from the viscosity related effects. In contrast, the reorientation times of DPP in neat [BMIM][N(CN)2] obey stick boundary condition as the hydrogen bond donating solute experiences specific interactions with the dicyanamide anion. No influence of the additive can be noticed on the rotational diffusion ...

Rotational diffusion of three structurally similar solutes, 9-phenylanthracene (9-PA), fluorescein (FL), and rhodamine 110 (R110), has been investigated in 1-butyl-3-methylimidazolium tetrafluoroborate-lithium tetrafluoroborate ([BMIM][BF4]-LiBF4) mixtures to understand the influence of the added electrolyte on the mobility of nonpolar, anionic, and cationic solute molecules. It has been observed that the reorientation times of the nonpolar solute 9-PA become progressively shorter with an increase in the concentration of LiBF4 at a given viscosity (η) and temperature (T). In the case of ionic solutes also, a decrease in the reorientation times has been observed upon the addition of the electrolyte compared to those obtained in the neat ionic liquid at a given η/T. However, this decrease is found to be independent of [LiBF4]. 9-PA being a nonpolar solute is located in the nonpolar domains of the ionic liquid. An enhancement in [LiBF4] leads to an increase in the sizes of the nonpolar domains resulting in the faster rotation of the solute. Anionic solute FL and cationic solute R110, which are located in the ionic region experience specific interactions with the cation and anion of the ionic liquid, respectively. In the presence of electrolyte, however, the strengths of these specific interactions diminish as the ions of the ionic liquid are not readily accessible to the solute molecules due to the organized structure, which results in faster rotation. These observations suggest that addition of LiBF4 induces a structure-making effect in the ionic liquid.

Rotational diffusion of a charged solute, rhodamine 110 (R110), and a nondipolar solute, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP), has been investigated in ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]) and 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([BMIM][FAP]), with 0.8 mole fraction of dibenzyl ether (DBE). This study has been undertaken to find out how specific interactions between the solute and the ionic liquid are affected upon dilution with a nondipolar solvent. It has been observed that at a given viscosity (η) and temperature (T), the reorientation times of R110 increase by 40-60% in the ionic liquid-organic solvent mixtures compared to ones in the corresponding neat ionic liquids. In the case of DMDPP, the influence of DBE is less pronounced, and its reorientation times increase by 25-50% at a given η/T. The addition of DBE weakens the numerous interactions prevailing between the cations and the anions of the ionic liquids, which results in stronger specific interactions between the solutes and the constituent ions, consequently leading to slower rotation of the solutes.

Rotational diffusion of two structurally similar nondipolar solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been examined in ethylammonium nitrate-lithium nitrate (EAN-LiNO3) mixtures to understand the influence of added electrolyte on the local environment experienced by the solute molecules. The measured reorientation times of both DMDPP and DPP in EAN-LiNO3 mixtures fall within the broad limits set by the hydrodynamic slip and stick boundary conditions. The hydrogen bond accepting DMDPP and the hydrogen bond donating DPP experience specific interactions with the cation and anion of the ionic liquid, respectively. Addition of LiNO3 (0.1 and 0.2 mole fraction) to EAN induces only viscosity related effects on the rotational diffusion of the two nondipolar solutes. These observations suggest that the local environment experienced by DMDPP and DPP in EAN is not altered upon the addition of LiNO3. Our results are consistent with the structural details available in the literature for EAN-LiNO3 mixtures.

Fluorescence anisotropies of two structurally similar nondipolar solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), have been measured in 1-methyl-3-octylimidazolium hexafluorophosphate-dibenzyl ether ([MOIM][PF6]-DBE) mixtures to understand how the addition of a low viscous nondipolar solvent influences solute rotation. The data when analyzed with Stokes-Einstein-Debye hydrodynamic theory reveals that the measured reorientation times of DMDPP are closer to the predictions of slip boundary condition, whereas those of DPP follow stick hydrodynamics. This outcome arises due to specific interactions between DPP and the solvent medium. Nevertheless, the important result of this study is that the rotational diffusion of DMDPP becomes gradually slower with an increase in the mole fraction of DBE (xDBE) for a given viscosity and temperature. In contrast, such a trend is not noticed for the hydrogen-bond donating solute DPP. Instead, two sets of reorientation times have been obtained, one corresponding to xDBE = 0.0-0.2 and the other xDBE = 0.4-1.0. The results for DMDPP have been rationalized on the basis of the organized structure of [MOIM][PF6], which attains homogeneity at the microscopic level with an increase in xDBE. In case of DPP, however, the propensity of the solute to be in the neighborhood of DBE, as a consequence of its stronger hydrogen bond accepting ability compared to the ionic liquid, appears to be the reason for the observed behavior.

To understand how the organized structure of the ionic liquids influences the location and mobility of nondipolar solutes, rotational diffusion of 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) has been examined in 1-alkyl-3-methylimidazolium (alkyl = ethyl, butyl, hexyl, and octyl) tetrafluoroborates. Both the solutes are structurally similar-the sole difference being the two NCH3 groups of DMDPP are replaced by two NH groups in DPP. The rotational diffusion of DPP is found to be significantly slower than DMDPP due to specific interactions between the NH groups of the solute and the anion of the ionic liquid. It has been observed that for a given viscosity and temperature, the rotational diffusion of DMDPP becomes progressively faster with an increase in the length of the alkyl chain on the imidazolium cation. DMDPP resides in the nonpolar domains of these ionic liquids whose sizes increase with an increase in the length of the alkyl chain, and as a result it experiences microviscosity that is lower than the bulk viscosity. However, an increase in the length of the alkyl chain has no apparent effect on the rotational diffusion of DPP because specific interactions with tetrafluoroborate necessitate the solute to be located in the vicinity of the anion. The results of this work exemplify that despite having similar size and shape, the rotational diffusion of DMDPP and DPP is quite contrasting as their sites of solubilization and the nature of interactions with the surroundings are vastly different owing to subtle variations in their chemical structures.

Rotational diffusion of two structurally similar organic solutes, 9-phenylanthracene (9-PA) and rhodamine 110 (R110), has been investigated in 1-methyl-3-octylimidazolium tetrafluoroborate-diethylene glycol ([MOIM][BF4]-DEG) mixtures to understand the influence of organic solvent on the organized structure of the ionic liquid. The reorientation times (τ(r)) of nonpolar and charged solutes have been measured as a function of viscosity (η) by changing the temperature (T) as well as the composition of the ionic liquid-organic solvent mixture. These results when analyzed using the Stokes-Einstein-Debye (SED) hydrodynamic theory follow the relationship τ(r) = A(η/T)(n), where A is the ratio of hydrodynamic volume of the solute to Boltzmann constant. However, in neat [MOIM][BF4] and up to 0.4 mole fraction of DEG (x(DEG)), significant deviations from the SED hydrodynamic theory have been noticed with n being much less than unity. As x(DEG) is increased further, the parameters A and n increase considerably for both solutes, and their rotational diffusion follows the predictions of the SED hydrodynamic theory. It has also been observed that the trends in the variation of τ(r) with η/T for 9-PA and R110 are not similar. These observations have been rationalized by taking into consideration the organized structure of the ionic liquid, which gradually becomes homogeneous at the microscopic level with the addition of the organic solvent.

Rotational diffusion of two structurally similar nonpolar and charged solutes has been examined in mixtures of an ionic liquid and an organic solvent of comparable size and viscosity with an intent to find out whether the organized structure of the former influences solute rotation. To this effect, temperature-dependent fluorescence anisotropies of 9-phenylanthracene (9-PA) and rhodamine 110 (R110) have been measured in n-propylammonium nitrate (PAN), propylene glycol (PG), and also four different compositions of PAN-PG mixtures. Analysis of the data carried out with the aid of Stokes-Einstein-Debye (SED) hydrodynamic theory indicates that the reorientation times of 9-PA and R110 scale more or less linearly with the ratio of viscosity to temperature and are found to be independent of the mole fraction of PAN. In other words, apart from the viscosity and temperature, rotational diffusion of both the solutes is not affected by the composition of PAN-PG mixtures. It has also been observed that the reorientation times of R110 are significantly longer compared to those of 9-PA due to the specific interactions prevailing between the cationic solute and PAN-PG mixtures. However, the important finding of this work is that, even though PAN forms an organized structure, rotational diffusion of the solute molecules is similar in both the ionic liquid and the organic solvent. The disordered lamellar structure present in PAN probably does not offer compact organized domains unlike ionic liquids with long alkyl chains wherein solute rotation is influenced significantly.

Rotational diffusion of a nonpolar solute 9-phenylanthracene (9-PA) and a cationic solute rhodamine 110 (R110) has been examined in a series of 1-alkyl-3-methylimidazolium (alkyl = octyl, decyl, dodecyl, tetradecyl, hexadecyl, and octadecyl) bis(trifluoromethylsulfonyl)imides to understand the influence of alkyl chain length on solute rotation. In this study, reorientation times (τr) have been measured as a function of viscosity (η) by varying the temperature (T) of the solvents. These results have been analyzed using the Stokes-Einstein-Debye (SED) hydrodynamic theory along with the ones obtained for the same solutes in 1-alkyl-3-methylimidazolium (alkyl = methyl, ethyl, propyl, butyl, and hexyl) bis(trifluoromethylsulfonyl)imides (Gangamallaiah and Dutt, J. Phys. Chem. B 2012, 116, 12819-12825). It has been noticed that the data for 9-PA and R110 follows the relation τr = A(η/T)(n) with A being the ratio of hydrodynamic volume of the solute to the Boltzmann constant and n = 1 as envisaged by the SED theory. However, upon increasing the alkyl chain length from methyl to octadecyl significant deviations from the SED theory have been observed especially from the octyl derivative onward. From methyl to octadecyl derivatives, the value of A decreases by a factor of 3 for both the solutes and n by a factor of 1.4 and 1.6 for 9-PA and R110, respectively. These observations have been rationalized by taking into consideration the organized structure of the ionic liquids, whose influence appears to be pronounced when the number of carbon atoms in the alkyl chain attached to the imidazolium cation exceeds eight.

To understand the influence of organized structure of the ionic liquids on the rotational diffusion of a hydrogen bond donating ionic solute, reorientation times (τr) of rhodamine 110 (R110) have been measured in 1-alkyl-3-methylimidazolium ([Rmim+]) based ionic liquids with anions tetrafluoroborate ([BF4-]) and hexafluorophosphate ([PF6-]). The viscosity (η) was varied by changing the temperature (T) and also the alkyl chain length on the imidazolium cation (ethyl, butyl, hexyl, and octyl). It has been noticed that τr versus η/T plots contain two slopes corresponding to lower and higher values of η/T for ionic liquids with [BF4-] as well as [PF6-] anions. For lower values of η/T (0.2 and0.3 mPa s K(-1), respectively, for [Rmim+][BF4-] and [Rmim+][PF6-]), rotational diffusion of R110 follows Stokes-Einstein-Debye hydrodynamic theory with stick boundary condition due to specific interactions between the solute and the anions of the ionic liquids. In contrast, at higher η/T, the rotational diffusion of the solute is faster than the stick predictions and this trend could not be explained by the quasihydrodynamic theories of Gierer-Wirtz and Dote-Kivelson-Schwartz as well. Diminishing hydrogen bonding interactions between the solute and the anions, which transpire as a consequence of the organized structure of the ionic liquids, are responsible for the observed behavior.

Fluorescence anisotropies of a nonpolar solute, 9-phenylanthracene (9-PA), have been measured in 1-alkyl-3-methylimidazolium (alkyl = methyl, butyl, octyl, and dodecyl) bis(trifluoromethylsulfonyl)imides ([RMIM][Tf2N]) with varying amounts (0–0.3 mole fraction) of lithium bis(trifluoromethylsulfonyl)imide (LiTf2N). This study has been carried out to understand how the length of the alkyl chain and the concentration of the electrolyte influence the rotational diffusion of a nonpolar solute. It has been observed that the addition of an electrolyte to the ionic liquid increases the bulk viscosity of the system significantly, as the Li+ cations strongly coordinate with the [Tf2N] anions in the polar domains. The reorientation times of 9-PA have been analyzed with the aid of Stokes–Einstein–Debye hydrodynamic (SED) theory, and they fall within the broad limits set by the hydrodynamic slip and stick boundary conditions. However, deviations from the SED theory have been noticed upon addition of LiTf2N, and the i...

In an attempt to find out whether the length of the alkyl chain on the imidazolium cation has a bearing on solute rotation, temperature-dependent fluorescence anisotropies of three structurally similar solutes have been measured in a series of 1-alkyl-3-methylimidazolium (alkyl = methyl, ethyl, propyl, butyl, and hexyl) bis(trifluoromethylsulfonyl)imides. Solute-solvent coupling constants obtained from the experimentally measured reorientation times with the aid of Stokes-Einstein-Debye hydrodynamic theory indicate that there is no influence of the length of the alkyl chain on the rotation of nonpolar, anionic, and cationic solutes 9-phenylanthracene (9-PA), fluorescein (FL), and rhodamine 110 (R110), respectively. It has also been noticed that the rotational diffusion of 9-PA is closer to the predictions of slip hydrodynamics, whereas the rotation of negatively charged FL and positively charged R110 is almost identical and follows stick hydrodynamics in these ionic liquids. Despite having similar shape and size, ionic solutes rotate slower by a factor of 3-4 compared to the nonpolar solute. Interplay of specific and electrostatic interactions between FL and the imidazolium cation of the ionic liquids, and between R110 and the bis(trifluoromethylsulfonyl)imide anion, appear to be responsible for the observed behavior. These results are an indication that the length of the alkyl chain on the imidazolium cation does not alter their physical properties in a manner that has an effect on solute rotation.

Temperature-dependent fluorescence anisotropies of two organic solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and rhodamine 110 (R110), have been measured in 1-butyl-3-methylimidazolium ([bmim(+)])-based ionic liquids containing the anions hexafluorophosphate ([PF(6)(-)]), bis(trifluoromethylsulfonyl)imide ([Tf(2)N(-)]), tetrafluoroborate ([BF(4)(-)]), trifluoromethanesulfonate ([TfO(-)]), and nitrate ([NO(3)(-)]). This data has been used in conjunction with the recently published results (Dutt, G. B. J. Phys. Chem. B2010, 114, 8971) for the same solutes in [bmim(+)] tris(pentafluoroethyl)trifluorophosphate ([FAP(-)]) to understand the influence of various anions on solute rotation. The boundary condition parameter C(obs), which has been obtained from the analysis of the data using Stokes-Einstein-Debye hydrodynamic theory, for the neutral solute DMDPP is more or less the same in all the ionic liquids. Moreover, C(obs) values are close to the predictions of slip boundary condition, which indicates that solvent viscosity alone governs the rotation of DMDPP. In contrast, for R110, which experiences specific interactions with the anions of the ionic liquids, the C(obs) values are close to stick hydrodynamics. It has also been noticed that the C(obs) values vary with the nature of the anion and this variation correlates with the hydrogen bond basicities of the anions of the ionic liquids.

To assess the influence of the nature of cation on solute reorientation, fluorescence anisotropies of two organic solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and rhodamine 110 (R110), have been measured in four ionic liquids containing tris(pentafluoroethyl)trifluorophosphate (FAP) anion over the temperature range 308-348 K. The ionic liquids used in the study are 1-butyl-1-methylpyrrolidinium FAP (BMPL FAP), 1-(2-methoxyethyl)-1-methylpyrrolidinium FAP (MOEMPL FAP), 1-(2-methoxyethyl)-1-methylpiperidinium FAP (MOEMPIP FAP), and N-(2-methoxyethyl)-N-methylmorpholinium FAP (MOEMMO FAP). Analysis of the data carried out with the aid of Stokes-Einstein-Debye hydrodynamic theory reveals that the rotation of the neutral solute DMDPP in all the four ionic liquids is essentially governed by the viscosity of the medium and the reorientation times follow slip boundary condition. In contrast, the results obtained for the cationic solute, which experiences specific interactions with the FAP anion, are somewhat different. The reorientation times of R110 are in between stick and slip limits and found to be independent of the nature of the cation of the ionic liquid except in case of highly viscous MOEMMO FAP, wherein it has been observed that the rotation of R110 is faster by a factor of 1.5. The observed behavior has been rationalized on the basis of highly associative nature of the MOEMMO cation, which precludes R110 from experiencing strong specific interactions with the FAP anion.

This article describes our ongoing efforts to understand dynamical processes such as rotational diffusion and photoisomerization in polymorphic environments of a block copolymer. The objective is to explore how the typical properties of a block copolymer solution such as critical micelle temperature (CMT) and temperature-induced sol-gel transition influence the rotational diffusion of hydrophobic solute molecules. Rotational diffusion of solute molecules differs significantly below and above the CMT of a block copolymer solution, while there is no influence of sol-gel transition on solute rotation. This is rationalized on the basis of the site of solubilization of the solute molecules which is the palisade layer of the micelles in both phases and unaffected by gelation. A similar result has been obtained in case of photoisomerization studies carried out with a carbocyanine derivative in the sol and gel phases of the block copolymer. The isomerization studies have been extended to the reverse phases (sol and gel phases) of the block copolymer to explore the nature of the water present in the cores of the reverse micelles. Our results provide evidence for the existence of water droplets with properties resembling bulk water. In essence, we show that despite having vastly differing bulk properties, both the solution and gel phases (normal as well as reverse) offer identical microscopic environment.

This paper gives an overview of the status and practice of forensic psychiatry in India. It traces the origins of mental health legislation and describes the fundamental aspects of criminal law as it relates to psychiatry, particularly with reference to provisions for diverting mentally disordered offenders (MDOs) to rudimentary and often non-existent mental health services. The archaic nature of mental health law, coupled with the criminal justice system's ignorance of underlying fundamental principles, affects thousands of MDOs. The breaches of human rights and absence of access to legal redress combine to highlight the lamentable condition of the MDO, an invisible group, despite recent efforts by the judiciary and the National Human Rights Commission of India. The research concludes by identifying core areas that require radical rethinking for the care and management of this dually disadvantaged group to reach acceptable standards.

Solute-solvent interactions play an important role in determining the physicochemical properties of liquids and solutions. As a consequence, understanding these interactions has been one of the long-standing problems in physical chemistry. This Minireview describes our approach towards attaining this goal, which is to investigate rotational relaxation of a pair of closely related, medium-sized nondipolar solutes in a set of appropriately chosen solvents. Our studies indicate that solute-solvent hydrogen bonding significantly hinders solute rotation. We have also examined the role of solvent size both in the absence and presence of specific interactions and it has been observed that the size of the solvent has a bearing on solute rotation especially in the absence of specific interactions. Our results point to the fact that only strong solute-solvent hydrogen bonds have the ability to impede the rotation of the solute molecule because, in such a scenario, hydrogen-bonding dynamics and rotational dynamics transpire on comparable time scales. This aspect has been substantiated by measuring the reorientation times of the chosen solutes in solvents such as ethanol and trifluoroethanol, which have distinct hydrogen-bond donating and accepting abilities, and correlating them with solute-solvent interaction strengths. As an alternative treatment, it has been shown that specific interactions between the solute and the solvent can be modeled as dielectric friction with the extended charge distribution model. This approach is not unrealistic considering the fact that specific as well as non-specific interactions are electrostatic by nature and the differences between them are subtle.

In an attempt to seek out whether the reorientation time of a solute molecule is influenced by marginal changes to its shape, rotational relaxation of four coumarin solutes that are almost identical in size but subtly distinct in shape has been investigated in a viscous nonpolar solvent as a function of temperature. It has been observed that the reorientation times of the four coumarins differ significantly from one another. The four solutes have been treated as asymmetric ellipsoids and Stokes-Einstein-Debye hydrodynamic theory has been employed to calculate the shape factors and boundary condition parameters. The measured reorientation times when normalized by respective shape factors and boundary condition parameters can be scaled on a common curve, which is an indication that ellipsoid based hydrodynamic theory is adequate to model the reorientation times even when the differences in the shapes of the solute molecules are minimal.

Rotational relaxation of two structurally similar nondipolar solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been examined in four isomeric butanols as a function of temperature in order to find out how the rotation of the solute molecules is influenced by the solute−solvent interaction strength. It has been observed that the hydrogen bonding interactions with the butanols do not influence the rotation of DMDPP. On the other hand, the rotation of DPP is affected by its interactions with the solvents, and as a result the reorientation times of DPP have been found to be over a factor of 2 longer than that of DMDPP. Two sets of reorientation times have been obtained, one corresponding to DMDPP and the other to DPP, when the reorientation times of both probes were normalized by the solvent viscosities. The observed pattern is a consequence of almost identical interaction strengths between the four isomeric butanols and the gi...

The interiors of the reverse micelles formed with the surfactant Triton X-100 (TX-100) in benzene−n-hexane mixed solvent with an increasing water content, W = [H2O]/[TX-100], have been explored by monitoring the fluorescence anisotropies of two structurally similar but chemically distinct hydrophobic probes. The objective of this work is to find out how the formation of the water pool influences the location and mobility of these probe molecules. It has been observed that the anisotropies of both the probes 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) decay as a sum of two exponentials with slow and fast time constants. This experimental finding has been rationalized on the basis of a two-step model according to which the probe molecule undergoes two different kinds of motion inside the micelle. The average reorientation times of DPP are a factor of 4 longer than that of DMDPP. This observation in conjunction with the fact that the ...

With an intent to address the question posed in the title, rotational diffusion of two dissimilar probes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and coumarin 6 (C6), has been investigated in small aqueous micelles formed with the surfactants sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), 2-phenyldodecanesulfonate (2-PDS), 3-phenyldodecanesulfonate (3-PDS), 4-phenyldodecanesulfonate (4-PDS), and 6-phenyldodecanesulfonate (6-PDS) using the time-resolved fluorescence depolarization method. The decay of anisotropy for both the probes in all the micelles could be adequately described by a sum of two exponentials with slow and fast time constants. These results have been rationalized on the basis of a two-step model consisting of fast-restricted rotation of the probe and slow lateral diffusion of the probe in the micelle that are coupled to the overall rotation of the micelle. From the order parameter values it has been established that the probes are located in t...

Rotational dynamics of a nondipolar solute, 2,5-dimethyl-1,4-dioxo-3, 6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and a dipolar solute, coumarin 6 (C6) has been studied in the isotropic phase of a liquid crystal, 4′-methoxybenzylidene-4-n-butylaniline (MBBA) to understand the influence of pseudonematic domains on the dynamics of dopant molecules. The reorientation times of both DMDPP and C6 follow the Stokes–Einstein–Debye hydrodynamic model instead of the Landau–de Gennes model, which is used to describe the rotational relaxation of neat isotropic liquid crystals. However, comparison of the data for both DMDPP and C6 in MBBA to that in an isotropic solvent, 1-decanol reveals that the probes are rotating considerably slower in the liquid crystal. These results indicate that ordered local structures of the liquid crystal exert more friction on the rotating solute molecule compared to an isotropic liquid.

Rotational dynamics of two structurally similar nondipolar probes; 2,5-dimethyl-1,4-dioxo-3,6diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) has been investigated in ethanol (EtOH) and 2,2,2-trifluoroethanol (TFE) in the temperature range 243–298 K in an attempt to understand how the strength of the solute–solvent hydrogen bond impedes molecular rotation. It has been observed that the reorientation times of DPP are slower compared to DMDPP by about a factor of 2 in EtOH and this factor is only 1.3–1.4 in TFE. Another interesting observation is that the viscosity normalized reorientation times of DPP at a given temperature are almost identical in EtOH and TFE, whereas those of DMDPP are slower by a factor of 1.5 in TFE compared to EtOH. These observations have been rationalized on the basis of hydrogen bond donating and hydrogen bond accepting abilities of the respective solute and the solvent. Further evidence for such a rationale has been provided with the aid of ab initio molecular orbital methods.

Rotational diffusion of two structurally similar hydrophobic probes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been studied in nonionic Brij-35 micelles as a function of temperature to explore the micellar internal environment. Analysis of the anisotropy data reveals that the probes are located in the interfacial region of the micelle and also undergo slow lateral diffusion and fast wobbling motion that are linked to the rotation of the micelle as a whole. From light scattering studies, it has been well-established that there is no variation in the size and hydration levels of Brij-35 micelles in the temperature range 283−323 K. Hence, it is logical to expect that there is no change in the site of solubilization of the probes in the micelles with temperature. An attempt has been made to determine the microviscosity of these micelles from the average reorientation times of the noninteracting probe DMDPP.

Rotational relaxation of three organic solutes, coumarin 6 (C6), 2,5-dimethyl-1, 4-dioxo3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP), and nile red (NR), that are similar in size but distinct in shape has been studied in a nonpolar solvent, squalane as a function of temperature to find out how the mechanical friction experienced by the solute molecule is influenced by its shape. It has been observed that C6 rotates slowest followed by NR and DMDPP. The results are analyzed using Stokes–Einstein–Debye (SED) hydrodynamic theory and also quasihydrodynamic theories of Gierer and Wirtz, and Dote, Kivelson, and Schwartz. Analysis of the data using the SED theory reveals that the measured reorientation times of C6 and DMDPP follow subslip behavior whereas those of NR are found to match slip predictions. While no single model could mimic the observed trend even in a qualitative manner, the reorientation times of C6 and DMDPP when normalized by their respective shape factors and boundary-condition parameters can be scaled on a common curve over the entire range of temperature studied. The probable reasons for the distinctive rotational behavior of NR as compared to C6 and DMDPP are explained in terms of its molecular shape and how this in turn influences the boundary-condition parameter are discussed.

In continuation of our efforts to understand the dynamics of solubilized species in large nonionic micelles, rotational relaxation of two structurally similar nondipolar probes, 2,5-dimethyl-1,4-di...

In an attempt to explore how electrolyte ions influence the friction experienced by solutes with different functional groups, rotational diffusion of two structurally similar coumarins, coumarin 34...

Sand-Stowing

Temperature dependent rotational relaxation studies of two structurally similar nondipolar probes: 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), have been carried out in Triton X-100 micelles in an attempt to explore the influence of specific interactions and micellar size on the dynamics of probe molecules. The time-resolved anisotropy in micelles, decays as a sum of two exponentials with two time constants, one corresponding to a fast reorientation time and the other to a slow one, for both the probes over the entire range of temperature studied. The results are analyzed in terms of a two-step model consisting of fast-restricted rotation of the probe and slow lateral diffusion of the probe in the micelle that are coupled to the rotation of the micelle as a whole. However, as the temperature is raised, the size of the Triton X-100 micelles increase significantly and the measured slow reorientation time corresponds solely to the lateral diffusion of the probe in the micelle. This is because the reorientation time for the overall rotation of the micelle becomes very long and consequently the fluorescence depolarization due to this process becomes negligible. It has also been observed that the short and long components of the anisotropy decay for DPP are found to be considerably slower than the corresponding ones for DMDPP due to the strong hydrogen bonding interactions between the ethylene oxide groups of the surfactant units and the secondary amino groups of the probe.

In a bid to explore how the presence of electrolyte ions influence the friction experienced by hydrogen bonding and nonhydrogen bonding solute molecules, rotational dynamics of two structurally similar nondipolar probes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been investigated in dimethylsulfoxide (DMSO) at several concentrations of LiNO3. The reorientation times of DMDPP, which does not strongly interact with the solvent, follow solution viscosity and dielectric parameters as the electrolyte concentration is increased. However, for DPP, which forms hydrogen bonds with DMSO, there is a 30% decrease in the viscosity-normalized reorientation times upon the addition of 2M LiNO3 due to the presence of electrolyte ions that shield the hydrogen-bonding interactions between the solute and the solvent. However, the reorientation times correlate well with the solution dielectric parameters with an increase in the electrolyte conce...

The rotational dynamics of 1-alkyl-3-methylimidazolium-based ionic liquids has been investigated by monitoring their inherent fluorescence with the intent to unravel the characteristics of the emitting species. For this purpose, temperature-dependent fluorescence anisotropies of 1-alkyl-3-methylimidazolium (alkyl = ethyl and hexyl) ionic liquids with anions such as tris(pentafluoroethyl)trifluorophosphate ([FAP]), bis(trifluoromethylsulfonyl)imide ([Tf2N]), tetrafluoroborate ([BF4]), and hexafluorophosphate ([PF6]) have been measured. It has been observed that the reorientation times (τr) of the ionic liquids with an ethyl chain scale linearly with viscosity and were found to be independent of the nature of the anion. The experimentally measured τr values are a factor of 3 longer than the ones calculated for 1-ethyl-3-methylimidazolium cation using the Stokes-Einstein-Debye (SED) hydrodynamic theory with stick boundary condition, which suggests that the emitting species is not the imidazolium moiety but some kind of associated species. The reorientation times of ionic liquids with a hexyl chain, in contrast, follow the trend τr([FAP])τr([Tf2N]) = τr([BF4])τr([PF6]) at a given viscosity (η) and temperature (T). The ability of the ionic liquids with longer alkyl chains to form the organized structure appears to be responsible for the observed behavior considering the fact that significant deviations from linearity have been noticed in the τr versus η/T plots for strongly associating anions [BF4] and [PF6], especially at ambient temperatures.

Rotational diffusion of a nondipolar solute 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and a charged solute rhodamine 110 (R110) has been investigated in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]) and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([BMMIM][Tf2N]) to understand the influence of the C2 methylation on solute rotation. The measured reorientation times of the nondipolar solute DMDPP are similar in both the ionic liquids and follow Stokes-Einstein-Debye hydrodynamic theory with slip hydrodynamics. In contrast, rotational diffusion of the charged solute R110 in [BMIM][Tf2N] obeys stick hydrodynamics due to specific interactions with the anion of the ionic liquid. Nevertheless, the intriguing result of this study is that the reorientation times of R110 in [BMMIM][Tf2N] deviate significantly from the predictions of stick hydrodynamics, especially at ambient temperatures. The solute-solvent boundary condition parameter Cobs, which is defined as the ratio of the measured reorientation time to the one calculated using the SED theory with stick boundary condition, for R110 is lower by a factor of 2 in [BMMIM][Tf2N] compared to [BMIM][Tf2N] at 298 K. Upon increasing the temperature, Cobs gradually increases and eventually matches with that obtained in [BMIM][Tf2N] at 348 K. It has been well established that methylation of the C2 position in [BMMIM][Tf2N] switches off the main hydrogen-bonding interaction between the anion and the cation, but increases the Coulombic interactions. As a consequence of the enhanced interionic interactions between the cation and anion of the ionic liquid, specific interactions between R110 and [Tf2N] diminish leading to the faster rotation of the solute. However, such an influence is not apparent in case of DMDPP as it does not experience specific interactions with either the cation or the anion of these ionic liquids.

Temperature dependent rotational relaxation study of neutral and cationic forms of neutral red has been carried out in dimethylsulfoxide (DMSO) in an attempt to find out how the charge on the solute influences its dynamics. Experimental results indicate that the cationic form rotates marginally slower (less than 20%) than the neutral form. The mechanical friction has been modeled using the Stokes–Einstein–Debye hydrodynamic theory with slip boundary condition and the dielectric friction using the extended charge distribution model of Alavi–Waldeck. The marginally slower reorientation times of the cationic form has been ascribed to the effect of dielectric friction. Alternatively, it has also been explained by invoking the concept of solute–solvent hydrogen bonding due to the presence of an additional hydrogen bonding site on the cation in the form of a hydrogen atom attached to the ring nitrogen. This result is different from that of the others in literature where cationic probes experience a lot more fri...

Rotational dynamics of three structurally similar coumarins; coumarin 6, coumarin 7, and coumarin 30 has been studied using a steady-state fluorescence depolarization technique. The idea is to understand how the friction experienced by a polar solute in a polar solvent depends on its dipole moment. Ab initio molecular orbital methods have been used to calculate the ground and excited state dipole moments. Although these coumarins are structurally similar their excited state dipole moments are quite different. Because of their similarity in shape and size they experience almost identical friction in alkanes, which is purely mechanical. However, in alcohols, the observed reorientation times do not follow the trend predicted by the dielectric friction theories of Nee–Zwanzig and van der Zwan–Hynes, based on their dipole moment values. Plausible reasons for the observed trend are discussed.

Rotational dynamics of two structurally similar nondipolar probes; 2,5-dimethyl-1,4-dioxo-3,6-di- phenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) has been studied in mixtures of squalane–1-butanol with the idea of finding out the role of size, chemical composition, and viscosity of the solvent on the friction experienced by hydrogen bonding (DPP) and nonhydrogen bonding (DMDPP) solute molecules. Although the reorientation times of both the probes followed a power law dependence on the solvent viscosity, DPP is found to rotate two to three times slower than DMDPP due to solute–solvent hydrogen bonding. The observed size effects of DMDPP have been modeled using the quasihydrodynamic theory of Gierer–Wirtz (GW). The rotational dynamics of DPP, however, follows stick hydrodynamics in the butanol rich region due to solute–solvent hydrogen bonding. But at higher concentrations of squalane, DPP gets preferentially located in a cagelike structure formed by butanol molecul...

The rotational reorientation times of two nonpolar probes, 2,5-dimethyl-1,4-dioxo-3, 6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) have been measured in 1-decanol and ethylene glycol as a function of temperature using steady-state fluorescence depolarization technique. Although both the probes are structurally similar and have almost identical volumes, the experimentally measured reorientation times of DMDPP are longer in ethylene glycol compared to 1-decanol whereas an exactly opposite trend has been observed for DPP. The faster rotation of DMDPP in 1-decanol has been attributed to the larger size of 1-decanol which is three times bulkier than ethylene glycol and hence offers a reduced friction. This pattern has been mimicked using the quasihydrodynamic theories of Gierer–Wirtz and Dote–Kivelson–Schwartz in a qualitative way. The slower rotation of DPP in 1-decanol compared to ethylene glycol is due to the solute–solvent hydrogen bonding which increases the effective volume of the probe more in the case of 1-decanol than ethylene glycol.

The rotational dynamics of two structurally similar nonpolar molecules, 2,5-dimethyl-1,4dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c] pyrrole (DPP) has been studied in glycerol in the temperature range of 300–380 K using both time-resolved and steady-state fluorescence depolarization techniques. While the reorientation times of both the probes are varying linearly as a function of viscosity over temperature, the rotational dynamics of DMDPP is described by the Stokes–Einstein–Debye hydrodynamic theory with slip boundary condition, whereas the reorientation times of DPP are in between slip and stick limits and are about a factor of 1.5 longer than that of DMDPP. This is due to the hydrogen bonding between the two NH groups of the probe molecule and the oxygen atoms of the hydroxyl groups in glycerol. It has also been observed that the rotational dynamics of a nonpolar and noninteracting molecule like DMDPP is essentially the same, both in glycerol and in n-alcohols.

Rotational reorientation times of two structurally similar nonpolar molecules, 2,5dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) have been measured in n-alcohols using steady-state fluorescence depolarization technique. While both DMDPP and DPP contain two C=O groups, the latter also has two NH groups. As these groups are known to form hydrogen bonds with alcohol solvents, the present work is aimed at finding out whether or not such solute–solvent hydrogen bonding is effecting the rotation of the probe molecules. The rotational dynamics of DMDPP is explained reasonably well by the Stokes–Einstein–Debye (SED) hydrodynamic theory with slip boundary condition. It is also found that the hydrogen bonding between the two C=O groups of the probe and the solvent molecules is not influencing the rotation of DMDPP. However, the reorientation times of DPP are found to be longer by a factor of 2.2 to 3.3 compared to that of DMDPP, and followed a super-stick behavior which has been observed for the first time for a nonpolar solute molecule. This is due to the strong hydrogen bonding between the two NH groups of the probe, and the alcoholic solvent molecules.

The effect of co-implantation of Si and Be in GaAs is discussed in the light of tailoring of a MESFET implantation profile. The modified profile is calculated by considering electrical activation and diffusion of both Si and Be in GaAs. The results compare well with a realized n-layer measured by the C–V technique. Since the pinch-off voltage is a figure of merit of device performance, a calculation of the latter using a tailored implantation profile is also presented in this paper.

Much of the fruit fly genome is compact ("Escherichia coli mode"), indicating a genome-wide selection pressure against DNA with little adaptive function. However, in the bithorax complex (BX-C) homeodomain genes are widely dispersed with large introns ("mammalian mode"). Chargaff difference analysis of compact bacterial and viral genomes has shown that most mRNAs have the potential to form stem-loop structures with purine-rich loops. Thus, for many taxa if transcription is to the right, the top (mRNA synonymous) DNA strand has purine-rich loop potential, and if transcription is to the left, the top (template) strand has pyrimidine-rich loop potential. The best indicator bases for transcription direction are A and T for AT-rich genomes, and C and G for CG-rich genomes. Consistent with this, Chargaff difference analysis of BX-C genes and several non-BX-C genes shows that, whatever the mode, mRNAs have the potential to form stem-loop structures with A-rich loops. We confirm that many potential open reading frames in the BX-C are unlikely to be functional. Conversely, we suggest that a few unassigned open reading frames may actually be functional. Since apparent organization in the mammalian mode cannot be explained in terms of unacknowledged open reading frames, yet the fruit fly genome is under pressure to be compact, it is likely that many BX-C functions do not involve the encoding of proteins.Key words: base ratios, base clusters, Chargaff's second parity rule, open reading frames, transcription direction, stem-loops.

Rotational diffusion of two ionic probes, cationic rhodamine 110 (R110) and anionic fluorescein (FL), has been examined in reverse micelles formed with the triblock copolymer (EO)13-(PO)30-(EO)13 (L64), where EO and PO represent ethylene oxide and propylene oxide units, respectively, with small amounts of water in p-xylene. This study has essentially been undertaken to explore the influence of mole ratio of water to copolymer (W) as well as copolymer concentration on probe rotation. On the basis of fluorescence lifetimes and reorientation times, it has been established that both R110 and FL are located in the interfacial region of L64/water/p-xylene reverse micellar system. The average reorientation time decreases by 10-35% with an increase in W for both the probes at a given copolymer concentration. However, for a particular W, the average reorientation time increases by 10-30% as the concentration of the copolymer is enhanced. From the micellar structural parameters available in the literature, critical packing parameters have been calculated for the L64/water/p-xylene reverse micellar system, and it has been noticed that the average reorientation times of both the probes scale linearly with the critical packing parameter. In essence, the results of this study indicate that the probe mobility in the interfacial region of block copolymer reverse micelles is governed by the micellar packing.

The photophysical properties of 2,9-di- n -pentyl-5,6,11,12-tetraazo-5,6,11,12-tetrahydrocoronene-5,6,11,12-tetracarboxy-bis- n -heptadecylimide (P5–17) in solution are investigated as a function of concentration. In 2-methyltetrahydrofuran, above 2 × 10 −5 M, a new absorption band with a maximum at 688 nm is observed indicating the formation of an aggregate. Upon excitation in this absorption band, emission from the aggregate with a maximum at 710 nm is observed. This emission coincides with that of the liquid crystalline discotic phase. The rotational dynamics of P5–17 and its aggregate are investigated using steady-state fluorescence measurements and time-resolved fluorescence anisotropy. From the global analysis of the polarised fluorescence decay traces, it is found that for both monomer and aggregate, the anisotropy decay can be described by a monoexponential decay law. The rotational correlation time for the monomer is linked over two excitation wavelengths corresponding to S 0 → S 1 and S 0 → S n transitions. For the aggregate, the excitation and emission dipoles are perpendicular and a fast fluorescence depolarization was observed.

The fluorescence anisotropy of two neutral and nonpolar molecules, 2,5,8,11-tetra-tert-butylperylene (TP) and 2,5,10,13-tetra-tert-butylterrylene (TT), is studied in a series of n-alcohols and alkanes. Both probes show an absorption band in the UV region and one in the visible region. The polarized fluorescence decay traces are globally analyzed over different excitation wavelengths. TP and TT can be modeled as oblate ellipsoids with essentially identical rotational correlation times. The anisotropy decay can well be approximated by a monoexponential model for both solvent series. The rotational correlation times (φ) vary linearly with viscosity (η) for both solvent series. Higher values for φ/η are reached in alkanes than in alcohols, the effect being more pronounced for TP than for TT. The predictions of the quasihydrodynamic models of Gierer−Wirtz and of Dote−Kivelson−Schwartz (DKS) are compared to the experimental data. Only the DKS model can predict qualitatively the experimental observations. The di...

Design procedures and the critical parameters contributing to the development of broadband, and low-noise mixer circuits at millimeter-wave frequencies are described. The circuit topologies, operating principles and design considerations for state-of-the-art millimeter-wave integrated circuit mixers are discussed and their typical performance characteristics arc presented. Planar microstrip, crossbar suspended stripline, and finline configurations are used in developing these high performance millimeter-wave integrated circuits.

Rotational diffusion of two pairs of structurally similar organic solutes has been examined in a protic ionic liquid, n-propylammonium nitrate (PAN), to understand the influence of specific interactions on solute rotation. It has been observed that the rotation of the nondipolar solute, 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) in PAN is 30-50% slower compared to its structurally similar counterpart 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP). Analysis of the data using Stokes-Einstein-Debye hydrodynamic theory indicates that the measured reorientation times of DMDPP and DPP are between the stick and slip limits. Furthermore, the rotation of the hydrogen bond accepting solute DMDPP was found to be 60% slower compared to the predictions of slip hydrodynamics, which has been rationalized on the basis of specific interactions between the solute and n-propylammonium cation of the ionic liquid. DPP, on the other hand, experiences specific interactions with both the anion and the cation of the ionic liquid due to the presence of hydrogen bond donating as well as accepting groups, resulting in slower rotation compared to DMDPP. The reorientation times of the ionic solutes fluorescein (FL) and rhodamine 110 (R110) are almost identical and closer to the predictions of stick hydrodynamics. The observed behavior is a consequence of the anionic solute FL and the cationic solute R110 experiencing hydrogen bonding interactions with n-propylammonium cation and nitrate anion, respectively. An attempt has also been made to rationalize these trends in terms of hydrogen bond acidity and basicity of PAN with the aid of existing scales, such as Kamlet-Taft and the Abraham model.

Photoisomerization of two carbocyanine derivatives has been examined in bis(2-ethylhexyl) sodium sulfosuccinate (AOT) reverse micelles to understand the factors that govern this process in the interfacial region of organized assemblies. To this effect, fluorescence lifetimes and quantum yields of 3,3(')-diethyloxadicarbocyanine iodide and merocyanine 540 have been measured in AOT∕isooctane∕water and AOT∕cyclohexane∕water reverse micellar systems as a function of the mole ratio of water to the surfactant, W. The nonradiative rate constants, which have been identified as the rates of photoisomerization for these solutes, were obtained from the experimentally measured parameters. The steady rise and subsequent saturation observed in the nonradiative rate constants upon increasing W has been rationalized in terms of micellar packing. An inverse correlation has been obtained between the nonradiative rate constants and the critical packing parameter, indicating that the interfacial friction experienced by the solute molecule is essentially described by this parameter.