Photophysical behaviour of 1-(4-N,N-dimethylaminophenylethynyl)pyrene (DMAPEPy) in homogeneous media (original) (raw)
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Dual Fluorescence of Phenyl and Biphenyl Substituted Pyrene Derivatives
The Journal of Physical Chemistry A, 2003
The photophysical properties of several acceptor substituted 1-arylpyrene derivatives were investigated. The fluorescence spectra strongly depend on the nature of the aryl moiety and the position and number of methoxycarbonyl acceptor groups. Dual fluorescence, originating from a locally excited and a charge transfer state, was observed for the diester derivatives. The solvent dependence of the dual fluorescence and the slightly curved solvatochromic plots indicate a change of the character of the excited states from solvents of low to high polarity. The rate constants for fluorescence and nonradiative decay were calculated to reveal the nature of the excited-state relaxation, that is, the increase of the mesomeric interactions by geometrical flattening or stabilization of the CT state by further twisting toward perpendicularity. Flattening is the major relaxation pathway of the diester phenylpyrene derivative in nonpolar solvents whereas in highly polar solvents the low value for the fluorescence transition dipole moment (M f) indicates stabilization of the charge transfer state by further twisting. The fluorescence of the diester biphenylpyrene derivative originates from a locally excited state (LE) in nonpolar solvents. The low value for M f in polar solvents and the change of the relative intensity of the dual fluorescence signals with the temperature indicate that the red-shifted fluorescence can be assigned to a twisted intramolecular charge transfer state.
The Journal of Physical Chemistry B, 2001
Picosecond transient absorption spectroscopy and picosecond spectro-streak fluorescence measurements have been carried out in order to understand the complex photophysical dynamics of directly linked donor-acceptor systems and the solvation dynamics in longer-chain alcohols. With these techniques, the fast solvent response to optically generated charge transfer (CT) species can be followed. Studies were performed on covalently linked donor-acceptor systems of the type pyrene with derivatives of N,N-dimethylaniline: dimethyl-(4pyren-1-yl-phenyl)-amine, dimethyl-(3-methyl-4-pyren-1-yl-phenyl)-amine and (3,5-dimethyl-4-pyren-1-ylphenyl)-dimethylamine. The results are interpreted with particular emphasis on solvation dependent electronic restructuring of the CT species. We suggest a mechanism where the adiabatic electronic restructuring coincides with the coupling to the torsional degrees of freedom of the solvent.
Journal of Photochemistry and Photobiology A-chemistry, 2011
Photophysical characterization of a molecule, trans-4- [4 -(N,N -dimethylamino)styryl]pyridine (4-DMASP) containing donor and acceptor moieties has been done experimentally as well as theoretically. Upon single excitation a charge-transfer state with high dipole moment is formed through rapid relaxation of a locally excited (LE) state in polar medium. A complete charge transfer process occurs as a result of twisting of donor group with respect to the acceptor part of the molecule resulting in the highly stabilized twisted state in polar medium giving fluorescence from LE state as well as from twisted state. However, in a nonpolar solvent emission occurs explicitly from a LE state. Hydrogen bond donor ability of solvents rather than dipolar interactions contributes more to the stability of ground state. However, dipolar interactions have greater contribution towards the stability of an excited state. All such interactions have higher contribution towards the stability of excited state than that of ground state. Very low fluorescence quantum yield in water is because of high rate of nonradiative processes as a result of high degree of stabilization of charge transfer state thereby making closer proximity of this state to triplet as well as ground charge transfer states. Monocation of 4-DMASP formed due to the protonation of pyridine nitrogen atom is more stable than neutral and dication species at ground as well as excited states because of greater extent of flow of charge from donor to acceptor part in monocation. Basicity of pyridine nitrogen atom being greater at excited state than that in ground state results in higher extent of pulling of charge from donor to acceptor part of monocation at excited state. Theoretical calculations suggest donor twisting as a possible path for creation of a charge transfer state rather than acceptor twisting. Excited state dipole moment value obtained from theoretical calculation corroborates well with the value determined experimentally. Theoretical calculation suggests no cis-trans photoisomerization in the ground state as well as excited state at room temperature.
Dyes and Pigments, 2014
Photophysical properties of trans-2-[4-(N,N-dimethylaminostyryl)]pyridine, a "pushepull" molecule, have been studied in different pure solvents. trans-2-[4-(N,N-dimethylaminostyryl)]pyridine exhibits fluorescence from a locally excited state in nonpolar solvents. However, in polar solvents, fluorescence occur from an intramolecular charge transfer state with high dipole moment obtained not only through the rapid relaxation of locally excited state upon a single excitation, but also by the excitation of ground intramolecular charge transfer state. The twisting of the donor moiety with respect to the acceptor moiety results in a complete charge transfer giving highly Stokes-shifted fluorescence in polar solvents. The potential energy surfaces along the donor and acceptor twist coordinates for the ground and first two singlet excited states have been evaluated at density functional theory and time dependent density functional theory levels, respectively. Monocationeneutral and dicationemonocation equilibria of trans-2-[4-(N,N-dimethylaminostyryl)]pyridine at both ground and excited states have been studied.
Chemical Physics, 2007
The fluorescence spectrum of 5-cyano-2-(1-pyrrolyl)-pyridine (CPP) was measured in several solvents as well as in an argon matrix. Based on comparison with other compounds and on ab initio calculations it is proposed that the fluorescence in the argon matrix and in non-polar solvents is due to two electronic excited states: one is of locally excited nature, the other a charge transfer (CT) state. In polar solvents the spectrum is dominated by the CT emission. The photo-physical behavior of CPP is discussed by comparison with that of other molecules exhibiting dual fluorescence and in view of a recent model developed for the benzene analog.
Dyes and Pigments, 2017
This study is focused on explanation of the remarkable photophysical behaviour of the 1-(4,6dichloro-1,3,5-triazin-2-yl)-pyrene (PyTC2) compound which has been introduced as a fluorescent polarity probe. This compound exhibits large solvatochromic red-shift of fluorescence emission band while maintaining high fluorescence quantum yield and monoexponential decay kinetics throughout the whole solvent polarity scale. As the semiempirical calculations reported in the original paper have not revealed any excited state possessing a high dipole moment, it has been suggested that the red-shift originates from planarization of the emitting excited state in polar solvents in contrast to unchanged twisted geometry in non-polar solvents. However, both the extent of the red-shift and the
Chemistry – A European Journal, 2020
Although 4-dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran (DCM) has been known for many decades as a bright and photostable fluorophore, used for a wide variety of applications in chemistry, biology and physics, only little attention has been paid so far to the presence of multiple isomers and conformers, namely s-trans-(E), s-cis-(E), s-trans-(Z), and s-cis-(Z). In particular, light-induced E-Z isomerization plays a great role on the overall photophysical properties of DCM. Herein, we give a full description of a photoswitchable DCM derivative by a combination of structural, theoretical and spectroscopic methods. The main s-trans-(E) isomer is responsible for most of the fluorescence features, whereas the s-cis-(E) conformer only contributes marginally. The non-emitting Z isomers are generated in large conversion yields upon illumination with visible light (e.g., 485 or 514 nm) and converted back to the E forms by UV irradiation (e.g., 365 nm). Such photoswitching is efficient and reversible, with high fatigue resistance. The E→Z and Z→E photoisomerization quantum yields were determined in different solvents and at different irradiation wavelengths. Interestingly, the fluorescence and photoisomerization properties are strongly influenced by the solvent polarity: the fluorescence is predominant at higher polarity, whereas photoisomerization becomes more efficient at lower polarity. Intermediate medium (THF) represents an optimized situation with a good balance between these two features.
Solvent effect, dipole moment, and DFT studies of multi donor–acceptor type pyridine derivative
Open Chemistry
A donor–acceptor substituted derivative 2,6-diamino-4-(3,4,5-trimethoxy-phenyl)-pyridine-3,5-dicarbonitrile (DTPP) has been synthesized and its photophysical properties have been studied. Effect of solvent on the photophysical features of DTPP has been undertaken by steady state absorption and emission techniques. Strong solvatochromic emission has been observed due to intramolecular charge transfer characteristics, upon changing the solvent polarity, revealing the highly polar character of the excited state. Dipole moment changes between the excited and ground state have been estimated by using the theory of solvatochromism from Lippert–Mataga and Reichardt’s correlations. The geometrical parameters for ground and excited states, conformational flexibility, and NLO behavior of the molecule have been theoretically investigated. The electronic distributions of DTPP in HOMO and LUMO were also investigated using density functional theory (DFT) methods at B3LYP/6-31 G** level. The corre...
Dual fluorescence of 4-dimethylaminopyridine and its derivatives
Journal of Photochemistry and Photobiology A: Chemistry, 2001
Electronic absorption and emission spectra of 4-(dimethylamino)pyridine (DMAP), 3-methyl-4-(dimethylamino)pyridine (MDMAP), and 3,5-dimethyl-4-(dimethylamino)pyridine (TMAP = tetramethylaminopyridine) were measured in cyclohexane (nonpolar), chloroform (medium polar), and acetonitrile (highly polar) solutions. Intense charge transfer emission of DMAP was observed only in acetonitrile, while that of MDMAP and TMAP was observed in all the three solvents. Dynamics of excited electronic states of these molecules is discussed on the basis of steric hindrance between methyl groups at 3-and 5-positions of pyridine ring and dimethylamino groups.