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Graphical abstract Highlights • Photophysical properties of a ratiometric amyloid probe have been investigated. • Role of solvent polarity and solute‐solvent H‐bonding on the amyloid sensing behavior of the sensor has been understood. • H-bonding with solvent leads to molecular twisting resulting large decrease in emission yield in polar protic solvents. Abstract Detailed photophysical properties of 2-[2′-Me,4′-(dimethylamino)-phenyl]benzothiazole (2Me-DABT), a potential ratiometric amyloid fibril sensor, have been investigated in different solvents and solvent mixtures using steady state and time-resolved spectroscopic techniques. Our studies show that emission properties of 2Me-DABT are significantly modulated by polarity of solvent media. Extent of solvatochromism (3585 cm−1) shown by 2Me-DABT is quite large and can be used to monitor micropolarity of different complex media. Further, Stokes' shift (>10,000 cm−1) shown by 2Me-DABT in all studied solvents is also much larger than most common molecular probes. It has also been shown that hydrogen bonding with solvent molecules results in large modulation in photophysical properties of 2Me-DABT. The H-bonding with water molecules induces a large change (39°) in the dihedral angle between benzothiazole and aniline moieties resulting large changes in photophysical properties of 2Me-DABT in polar protic solvents. Photophysical properties reported herein are used to explain observed amyloid sensing behaviour of 2Me-DABT. Detailed quantum chemical calculations are performed to support the experimental results. [ABSTRACT FROM AUTHOR]

The fluoren-9-one (FL) molecule, with a single hydrogen bond-accepting site (CO group), has been used as a probe for investigation of the dynamics of a hydrogen bond in its lowest excited singlet (S1) state using the subpicosecond time-resolved visible pump-IR probe spectroscopic technique. In 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), a strong hydrogen bond-donating solvent, the formation of an FL-alcohol hydrogen-bonded complex in the ground electronic (S0) state is nearly complete, with a negligible concentration of the FL molecule remaining free in solution. In addition to the presence of a band due to the hydrogen-bonded complex in the transient IR spectrum recorded immediately after photoexcitation of FL in HFIP solution, appearance of the absorption band due to a free CO stretch provides confirmatory evidence of ultrafast photodissociation of hydrogen bonds in some of the complexes formed in the S0 state. The peak-shift dynamics of the CO stretch bands reveal two major relaxation pathways, namely, vibrational relaxation in the S1 state of the free FL molecules and the solvent reorganization process in the hydrogen-bonded complex. The latter process follows bimodal exponential dynamics involving hydrogen bond-making and hydrogen bond-reorganization processes. The similar lifetimes of the S1 states of the FL molecules, both free and hydrogen-bonded, suggest establishment of a dynamic equilibrium between these two species in the excited state. However, investigations in two other weaker hydrogen bond-donating solvents, namely, trifluoroethanol (TFE) and perdeuterated methanol (CD3OD), reveal different features of peak-shift dynamics because of the prominence of the vibrational relaxation process over the hydrogen bond-reorganization process during the early time. [ABSTRACT FROM AUTHOR]

Highlights: [•] Femtosecond excited state dynamics of 1-nitropyrene, an environmental pollutant, has been studied. [•] Experimentally for the first time it has been shown that rotation of the nitro group in nitropyrene takes place in its photoexcited state. [•] In protic solvent, due to solute–solvent H-bonding interaction, rotation of the nitro group is absent. [ABSTRACT FROM AUTHOR]

The article presents a study on the effect of varying amounts of organoclay on the morphology, mechanical, thermal and rheological properties of polymer nanocomposites prepared by melt intercalation technique. Results show that organoclay has no significant effect on hard segment hydrogen bonding but increasing clay content increases viscosity and storage modulus. Cloisite 15A clays are found to be more prone towards the soft segment domain and that nanocomposites are composed of well dispersed, intercalated, exfoliated silicate layers in the matrix.

Water molecules in reverse micelle serve as an excellent model for biological water. However, it has been argued previously that water molecules at the centre, even for smaller sized water pools of reverse micelles, behave like bulk water, using ultrafast vibrational lifetime measurements of azide ion. In the present investigation, the vibrational dynamics of an ultrasmall IR probe, azide ion, has been studied in AOT reverse micelle, at various w 0 (radius of water pool), using linear IR measurements, vibrational lifetime measurements and 2D-IR measurements. While linear IR measurements show gradual variation in spectral parameters, such as, peak position and width of the vibrational transition, suggesting a gradual change in the micro environment of the probe with variation in radius of the water pool, the vibrational lifetime remains indistinguishable with variation in w 0 , which has been ascribed earlier to the location of azide ion in the centre of the water pool. Herein, ultrafast 2DIR spectroscopy convincingly demonstrates that, for a smaller sized water pool, the water molecules, even at the centre of the water pool, behave significantly different as compared to bulk water, an inference, which is missed by the previous vibrational lifetime measurements, and suggest an extensive slowdown of the hydrogen bond relaxation dynamics as compared to bulk water. • The Vibrational dynamics of azide ion has been studied in AOT reverse micelle. • The vibrational lifetime remains invariant with variation in radius of water pool • Ultrafast 2D-IR spectroscopy demonstrates variation in FFCF with water pool size. • For small W 0 , the core water molecules behave differently compared to bulk water. [ABSTRACT FROM AUTHOR]

Schematic diagram to show conventional and aromatic π-hydrogen bonding interactions between the excited (S 1) state of 9-ACD and the Trifluoroethanol (TFE) solvent molecules. TRIR spectrum of the S 1 state of 9-ACD in TFE at 0.3 ps delay time reveals overlapping of the IR bands of hydrogen bonded carbonyl stretch and the ring mode vibration of the aromatic anthracenyl moiety. However, at 75 ps delay time, these two spectra are resolved because the peak wavenumber of the ring mode vibration suffers a dynamic blue shift due to hydrogen bond reorganization process, which leads to strengthening of the aromatic π-hydrogen bonding interaction. [Display omitted] • Effect of solvent polarity and hydrogen bonding interaction on the excited state dynamics of 9-Anthracenecarboxaldehyde (9-ACD)have been investigated using steady state and time-resolved electronic and vibrational spectroscopic techniques. Photophysical properties and dynamics of the excited states are seen to be more sensitive to intermolecular hydrogen bonding interaction with the solvent, rather than its polarity. • FTIR studies reveal formation of complexes with the protic solvents via formation of conventional hydrogen bond at the carbonyl site of 9-ACD molecule. In strong hydrogen bond-donating solvents, namely, 2, 2, 2-trifuoroethanol (TFE) and 1, 1, 1, 3, 3, 3-hexafluoroisopropanol (HFIP), nearly all the molecules of 9-ACD in solution remain engaged in complex formation with insignificant number of molecules remaining free in solution. In aprotic solvents, the S 1 state is short-lived (lifetime is only a few tens of ps) and intersystem crossing (ISC) is the major deactivation pathway (the triplet yield is near unity). However, in strong hydrogen bond donating solvents, the S 1 state lifetime is long (a few ns) because the deactivation pathway for the S 1 state via the triplet manifold is blocked. • Both the ultrafast time-resolved electronic and vibrational spectroscopy studies in TFE and HFIP reveal that hydrogen bond reorganization process following photoexcitation of the hydrogen bonded complex is the only relaxation process undergone by the S 1 state in sub-100 ps time domain. However, the time-resolved IR (TRIR) spectroscopy studies further reveal the possibility of formation of aromatic π-hydrogen bonding and/or reorganization of the hydrogen bond at this site, which makes the major contribution towards the S 1 state relaxation process. Effect of solvent polarity and hydrogen bonding interaction on the excited state dynamics of 9-Anthracenecarboxaldehyde (9-ACD) have been investigated using steady state and time-resolved electronic and vibrational spectroscopic techniques. Photophysical properties and dynamics of the excited states are seen to be more sensitive to intermolecular hydrogen bonding ability of the solvent, rather than its polarity. FTIR studies reveal formation of complexes with the protic solvents via formation of conventional hydrogen bond at the carbonyl site of 9-ACD molecule. In strong hydrogen bond donating solvents, namely, 2, 2, 2-trifuoroethanol (TFE) and 1, 1, 1, 3, 3, 3-hexafluoroisopropanol (HFIP), nearly all the molecules of 9-ACD in solution remain engaged in complex formation leaving insignificant number of molecules remaining free in solution. In aprotic solvents, the S 1 state is short-lived (the lifetime is only a few tens of ps) and intersystem crossing (ISC) is the major deactivation pathway (the triplet yield is near unity). However, in strong hydrogen bond donating solvents, the S 1 state lifetime is long (a few ns) because the deactivation pathway for the S 1 state via the triplet manifold is blocked. Both the ultrafast time-resolved electronic and vibrational spectroscopy studies in TFE and HFIP reveal that hydrogen bond reorganization process following photoexcitation of the hydrogen bonded complex is the only relaxation process undergone by the S 1 state in sub-100 ps time domain. However, the time-resolved IR (TRIR) spectroscopy studies further reveal the possibility of formation of aromatic π- hydrogen bonding and reorganization of the hydrogen bond at this site makes the major contribution towards the S 1 state relaxation process in strong hydrogen bond donating solvents. [ABSTRACT FROM AUTHOR]