We have synthesized a new environment-sensitive fluorophore, 6-N,N-dimethylamino-2,3-naphthalimide (6DMN). This chromophore exhibits valuable fluorescent properties as a biological probe with emission in the 500−600 nm range and a marked response to changes in the environment polarity. The 6DMN fluorescence is red-shifted in polar protic environments, with the maximum emission intensity shifting more than 100 nm from 491 nm in toluene to 592 nm in water. Additionally, the fluorescence quantum yield decreases more than 100-fold from chloroform (Φ = 0.225) to water (Φ = 0.002). The scope and applications of the 6DMN probe are expanded with the synthesis of an Fmoc-protected amino acid derivative (5), which contains the fluorophore. This unnatural amino acid has been introduced into several peptides, demonstrating that it can be manipulated under standard solid-phase peptide synthesis conditions. Peptides incorporating the new residue can be implemented for monitoring protein−protein interactions as exemplif...

Photophysics and Biological Applications of the Environment-Sensitive Fluorophore 6-N,N-Dimethylamino-2,3-naphthalimide

The photophysical properties of 7-amino-4-trifluoromethyl-1,2-benzopyrone (coumarin-151; C151) in nonpolar (NP) solvents are drastically different than those in other solvents of moderate to higher polarities. Thus, the absorption and fluorescence maxima are largely blue-shifted and the Stokes' shifts unusually low in NP solvents compared to those in the other solvents. The fluorescence quantum yields (Φf) in NP solvents are also exceptionally lower. While in all other solvents the fluorescence decays of C151 are single-exponential, in NP solvents the decays show non-single-exponential behavior. The average fluorescence lifetimes (τf) in NP solvents are also substantially shorter. Low Φf and τf values in NP solvents indicate very fast nonradiative deactivation for the S1 state of C151. Investigating the triplet characteristics of C151 by using picosecond laser flash photolysis and pulse radiolysis techniques, it has been established that the fast nonradiative deactivation in NP solvents is not due to an e...

Unusual Photophysical Properties of Coumarin-151

Excited-state dipole moments of a set of Coumarin dyes extensively used in laser applications have been determined for the first time, employing a solvatochromic procedure utilising the microscopic solvent polarity parameter, ENT. Our results are expected to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts is superior to that obtained using bulk solvent polarity functions. The experimentally determined dipole-moment changes are in fair agreement with recent semi-empirical computational predictions. It is shown that the discrepancies observed in some cases can be overcome using more appropriate parametrisation in the calculation. The insight provided by the present measurements into the nature of the emitting state is mentioned.

Excited-state dipole moments of some Coumarin dyes from a solvatochromic method using the solvent polarity parameter, ENT

Room temperature ionic liquids, particularly those based on the imidazolium salts, have emerged in recent years as highly promising “green” media suitable for carrying out various reactions. In this paper, picosecond time-resolved fluorescence decay behavior of three electron donor−acceptor (EDA) molecules, coumarin-153 (C153), 6-propionyl-2-dimethylaminonaphthalene (PRODAN), and 4-aminophthalimide (AP), in two room temperature ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][(CF3SO2)2N]) and 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([BMIM][(CF3SO2)2N]), has been reported. The steady-state fluorescence behavior of the EDA molecules suggests that the polarity of the two ionic liquids in the ET(30) scale is around 47.6 for [EMIM][(CF3SO2)2N] and 47.1 for [BMIM][(CF3SO2)2N]. The fluorescence decay behavior of the systems in these media has been found to be dependent on the monitoring wavelength, suggesting solvent-induced relaxation of the fluoresce...

Dynamics of Solvation of the Fluorescent State of Some Electron Donor−Acceptor Molecules in Room Temperature Ionic Liquids, [BMIM][(CF3SO2)2N] and [EMIM][(CF3SO2)2N]

Photophysical behavior of two series of 4-amino-1,8-naphthalimide derivatives differing in the amino functionality has been studied as a function of the polarity of the medium. The location of the lowest singlet state of the systems, intramolecular charge transfer (ICT) in nature, is largely controlled by the conformation of the 4-amino group rather than its electron-donating ability. The fluorescence properties of the systems are strongly dependent on the nature of the amino group as well as on the polarity of the media. An increase in the length of the dialkyl groups connected to the amino nitrogen or an increase in the size of the ring containing the amino nitrogen enhances the nonradiative deactivation of the fluorescent state of the molecule. The nonradiative relaxation process is facilitated by an increase in the polarity of the media. The present results suggest that the radiationless deactivation of the fluorescent state of the systems is dependent on the nitrogen inversion rate at the amino group.

Influence of the Structure of the Amino Group and Polarity of the Medium on the Photophysical Behavior of 4-Amino-1,8-naphthalimide Derivatives

It is shown that the solvatocbromism of Stokes shifts has superior correlation with the solvent polarity function E T N , and the theoretical basis for this is analyzed. The estimation of reliable excited state dipole moments from this correlation as well as the practical advantage of the method in terms of the possibility of employing mixed solvents is demonstrated.

Excited state dipole moments from an efficient analysis of solvatochromic stokes shift data

Donor-acceptor substituted quinonoid molecules have been investigated very tittle in connection with nonlinear optical (NLO) applications. We present a theoretical analysis of the hyperpolarizability, β, of a model push-pull quincnold molecule as a function of the quinonoid-benzenoid character (QBC). β is found to be quite large at all geometries except the quinonoid extreme; it results from appreciable contributions from a large number of excited states.

Analysis of the Large Hyperpolarizabilities of Push-Pull Quinonoid Molecules

A series of amine donor-substituted dicyanoquinodimethane molecules with large calculated hyperpolarizabilities has been investigated. Molecular and crystal structure details of a prototypical system are presented. Moderate to strong phase-matched powder second-harmonic generation is observed in chiral amine-substituted compounds.

Strong optical second-harmonic generation in a chiral diaminodicyanoquinodimethane system

Strong solvate-switchable second harmonic generation has been observed in powders of 7,7-dipyrrolidino-8,8-dicyanoquinodimethane.

M. Ravi

Papers

Excited-state dipole moments of some Coumarin dyes from a solvatochromic method using the solvent polarity parameter, ENT

Excited state dipole moments from an efficient analysis of solvatochromic stokes shift data

Analysis of the Large Hyperpolarizabilities of Push-Pull Quinonoid Molecules

Strong optical second-harmonic generation in a chiral diaminodicyanoquinodimethane system

Solvate-switchable powder second harmonic generation in a push–pull quinonoid system