A fluorescence emission study of nitro- and nitromethyl-substituted 1,4-diarylbutadienes in solid state

1-(4-Nitrophenyl)-4-phenylbuta-1E,3E-diene 1, 1,4-di (4-nitrophenyl)buta-1E,3E-diene 2, 1-phenyl-2-methyl-4-(4-nitrophenyl) buta-1E,3E-diene 3, and 1-4-di (4-nitrophenyl)-2-methylbuta-1E,3E-diene 4 have been synthesized and their fluorescence emissions in solid state in comparison with their ambient temperature fluorescence emissions in organic solvents of varying relative permittivity and in ethanol-methanol matrix at 77 K have been investigated. It has been found that while the UV-vis absorption of the dienes in solution phase largely remains unaffected by solvent polarity, the fluorescence maximum (lambda (f) max) gets significantly altered and a much red-shifted lambda (f) max is observed in solvents of relatively higher relative permittivity (e.g. polar solvents like acetonitrile and methanol). In ethanol-methanol glass at 77 K, the fluorescence of the dienes gets significantly blue-shifted. In solid state also a red-shifted fluorescence is observed, but the red-shift is not as pronounced as in polar solvents. However, it is significantly red-shifted as compared to in solvents having relatively lower relative permittivity (e.g. the non-polar solvents like 1,4-dioxane and THF). The fluorescence spectra of nitro-dienes, particularly 2 and 4 in solid state are significantly red-shifted as compared to their fluorescence emission in relatively non-polar solvents. Further, for the mono-nitro substituted dienes I and 3, the solid state fluorescence emission is similar to that observed in relatively non-polar solvents. The results have been discussed in terms of the singlet excited states of the dienes having different polarity and geometry. It has been suggested that in solution phase in addition to the fluorescence emission from the initially prepared planar locally excited state, the fluorescence emission in these dienes can occur from intramolecular charge transfer excited state and in some cases even from a non-planar, dipolar conformationally relaxed intramolecular charge transfer excited state. The red-shifted emission of these dienes in solid state when compared to that in relatively less polar solvents, and in another highly condensed media such as ethanol-methanol glass at 77 K indicates that the solid state fluorescence of the dienes does not originate from conformationally relaxed excited states. The solid state fluorescence emission of the dienes has been attributed to excimer and intramolecular charge transfer excited state with planar geometry. Further, the role of energy level re-ordering of the two lowest excited states of the dienes, influencing the fluorescence properties has also been discussed

Effect of microheterogeneous media on the fluorescence and fluorescence probe properties of donor-acceptor diarylbutadienes

Diarylbutadienes, namely 1-(para-cyanophenyl)-4-phenylbuta-1E,3E-diene (1), 1-(para-methoxyphenyl)-4-phenylbuta-1E,3E-diene (2), 1-(para-cyanophenyl)-4-(para-methoxyphenyl)-1E,3E-diene (3) have been prepared and investigated for their absorption and fluorescence properties in homogeneous media of organic solvents, dioxane-water binary mixtures and in the microheterogeneous media of sodium dodecyl sulfate, cetyl trimethyl ammonium bromide and Triton-X-100 micelles. The fluorescence behaviour in various media has been correlated in terms of empirical solvent parameters such as Dimroth E-T(30) and Kamlet-Taft pi* values, and Kirkwood functions. A Linear correlation between solvent polarity and fluorescence properties is observed. In ethanol-methanol (1:1, v/v) matrix at 77 K, a blue-shifted fluorescence maximum with enhanced fluorescence quantum yields is observed for dienes 2 and 3. The singlet excited state of diene 3 is found to be highly polar in nature. The fluorescence peak intensity of dienes 1 and 2 and the fluorescence emission wavelength maximum (lambda(f), max) of diene 3 undergo significant changes upon changing the concentration of surfactants. The fluorescence properties of these dienes have been further used to characterize the micelles in terms of their critical micelle concentration and micropolarity

Photophysical studies of substituted 1,2-diarylethenes: twisted intramolecular charge transfer fluorescence in dimethoxycyano-substituted 1,2-diarylethene

1,2-Diarylethenes, namely (E)-1-(4-cyanophenyl)-2-phenylethene (1), (E)-1-(4-methoxyphenyl)-2-phenylethene (2), (E)-1-(3,4-dimethoxyphenyl)-2-phenylethene (3), (E)-1-(4-cyanophenyl)-2-(4-methoxyphenyl)ethene (4) and (E)-1-(4-cyanophenyl)-2-(3,4-dimethoxyphenyl)ethene (5), have been synthesized and their absorption and fluorescence properties at room temperature in different organic solvents and also in 1,4-dioxane-water binary mixtures have been investigated. Additionally, the fluorescence of these compounds has been examined at 77 K in an ethanol-methanol (1:1 v/v) matrix. Photophysical parameters like absorption, excitation and fluorescence spectra, fluorescence quantum yields, excited state dipole moment changes, and correlation of solvatochromic fluorescence with solvent parameters like E-T(30)-values and the pi*-scale have been made. Compound 5, with one cyano and two methoxy substituents, has been found to exhibit solvent polarity-dependent dual fluorescence. The shorter wavelength fluorescence is attributed to an initially excited delocalized planar state, while the longer wavelength fluorescence is attributed to a non-planar twisted intramolecular charge transfer excited state

alpha,omega-diphenylpolyenes cabable of exhibiting twisted intramolecular charge transfer fluorescence: A fluorescence and fluorescence probe study of nitro- and nitrocyano-substituted 1,4-diphenylbutadienes

1,4-Diphenylbutadiene compounds, namely 1-p-cyanophenyl-4-phenylbuta-1E,3E-diene (2), 1-p-nitrophenyl-4-phenylbuta-1E,3E-diene (3), 1-cyano-1,4-diphenylbuta-1Z,3E-diene (4), 1-p-cyanophenyl-4-p-nitrophenylbuta-1E,3E-diene (5), 1-cyano-1-p-nitrophenyl-4-phenylbuta-1Z,3E-diene (6), and 1-cyano-1-phenyl-4-p-nitrophenylbuta-1Z,3E-diene (7), have been synthesized and their absorption and fluorescence properties in organic solvents, water-dioxane, and SDS, CTAB, and Triton-X-100 micelles have been investigated. The fluorescence behavior of these dienes has also been examined in ethanol-methanol (1:1) matrix at 298 and 77 K. The dienes with nitro substituents on the aromatic ring are capable of exhibiting dramatically redshifted fluorescence emission due to twisted intramolecular charge-transfer excited states. The fluorescence properties of nitro-substituted dienes 3, and 5-7 have been utilized to probe the microenvironment of SDS and CTAB micelles Ln terms of dielectric constant of water-micelle interface, location of the probe molecules in the micelles, and the cme values. This study has brought out interesting features of the excited state structure and potential energy surface of diphenylpolyenes. It further provides new directions for the development of fluorescence probes as sensors and reporters of microenvironments of organized assemblies

Twisted intramolecular charge transfer fluorescence in nitro-substituted alpha,omega-diphenylpolyene compounds

A fluorescence study of 1-p-cyanophenyl-4-phenylbuta-1E,3E-diene (2), 1-p-nitrophenyl-4-phenylbuta-1E,3E-diene (3), and 1-p-nitrophenyl-4-p-cyanophenylbuta-1E,3E-diene (4) in solvents of varying polarity at ambient temperature and in a 1:1 ethanol-methanol matrix at 298 and 77 K revealed that the nitro-substituted compounds are capable of exhibiting unusually red-shifted fluorescence emissions due to a twisted intramolecular charge transfer excited state

Amino substituted 4-pyridylbutadienes: synthesis and fluorescence investigations

Synthesis and spectroscopic investigations of a series of donor-π-acceptor systems containing pyridine as the electron withdrawing group and an amino derivative (dimethylamino, diphenylamino, carbazole and julolidine) as electron donating group, separated by a π-spacer are described. The effect of varying donors on absorption and emission properties was studied in different solvents. All the molecules investigated exhibit pronounced positive polarity dependent solvatochromic shifts of up to ∼141 nm. Strong fluorescence quantum yields are also observed for dienes containing carbazole and diphenylamine donors. This behavior suggests the presence of highly polar emitting states as a result of π -π* intramolecular charge-transfer (ICT). The observations were corroborated by a linear relation of the fluorescence maximum (νmax) versus the solvent polarity function (Δf) from the Lippert–Mataga correlation. The emission lifetime shows a decay profile consistent with the formation of one species (1 and 3) and two species (2 and 4) in the excited state.by Harsha Agnihotri, et.a

Biocompatible Naphthyl Derivatives as Preferential Stabilizer of Quadruplex DNA

by Beena Kumari, Sushree S. Pany, P. I. Pradeepkumar and Sriram Kanva

Single-Molecule Cholesterol Sensing by Integrating Silver Nanowire Propagating Plasmons and Graphene Oxide π‑Plasmons on a Photonic Crystal-Coupled Emission Platform

The escalating concern about ohmic losses in metal-dependent plasmonics demands more effective material fabrication for the development of biosensing frameworks. The omnidirectionality and low signal collection efficiency of a conventional fluorescence-based detection platform make it challenging to realize better sensitivity for real-time point-of-care diagnostics. In an attempt to address these demands, recently a photonic crystal-coupled emission (PCCE) platform has been demonstrated to outperform the well-established surface plasmon-coupled emission platform for biophysicochemical sensing applications. The effects of the different numbers of bilayers (BLs) of a one-dimensional photonic crystal (1DPhC) on the electric field intensity of Bloch surface waves and internal optical modes (IOMs) are extensively studied in this work to improve the performance of the PCCE platform rationally. Specifically, the 1DPhC with 10 BLs presented 55-fold PCCE enhancements because of the strong field confinement by the IOMs and small losses. In addition, the critical role of nanoengineering graphene oxide π-plasmon and silver nanowires on the PCCE platform has been explored to yield an unprecedented >1300-fold increase in fluorescence intensity. The amplified PCCE enhancements obtained with the first experimental evidence of the synergism among dielectric plasmons (1DPhC), graphene oxide plasmons, and metal plasmons (from silver nanowires) have been utilized to sense cholesterol at the single-molecule limit of detection. The photoplasmonic sensor presented here exhibits potential utility in academia and industry and provides a perspective for combining materials at nanoregimes for the desired applications