What Determines the Rate of Excited‐State Intramolecular Electron‐Transfer Reaction of 4‐(N,N′‐dimethylamino)benzonitrile in Room Temperature Ionic Liquids? A Study in [bmim][PF6]

Room temperature ionic liquids (ILs) are a new type of solvent with peculiar properties. ILs are usually composed of an anion and a bulky cation with one or more alkyl chains to decrease the melting point. These structural peculiarities lead to the high viscosity and the heterogeneity of ILs, which could affect chemical reactions. In the present perspective, we will first introduce the experimentally observed nature of the heterogeneous liquid structure and then introduce recent developments in the study on electron transfer (ET) and charge transfer (CT) reactions in relation with the solvation and the heterogeneity of ILs. Because of the high viscosity of ILs, diffusive solvation is expected to be slow which could be the rate-limiting factor for ET and CT processes. However, ILs could provide a unique reaction field depending on the location of the solute within the heterogeneous liquid structure and the reaction could be faster than that expected from the bulk viscosity due to the fast fluctuation of the local environment.

Section: Et and Ct Reactions In Ilmentioning

confidence: 99%

Section: Et and Ct Reactions In Ilmentioning

confidence: 99%

Ultrafast solvation dynamics and charge transfer reactions in room temperature ionic liquids

Nagasawa

Miyasaka

2014

“…Among many donor-acceptor substituted chromophores, the most widely studied, and the one that continues to attract research attention, is 4-(dimethylamino)benzonitrile (DMABN). 18,19 This molecule shows dual emission bands; a blue emission arising from the locally excited (LE) state and a red emission from the ICT state, the latter being highly stabilized in polar solvents. Since the first report of this interesting phenomenon by Lippert et al in 1961, 20 several models have been proposed to elucidate the occurrence of dual fluorescence and to characterize the ICT state of DMABN and other structurally related molecules.…”

Section: Introductionmentioning

confidence: 99%

A study on the photophysics of 9-amino-10-cyanoanthracene: probing its dual absorption and emission behavior

Choudhury

Muralidharan

Pal

2014

The photophysics of a donor-acceptor substituted chromophore, 9-amino-10-cyanoanthracene (ACAN), has been investigated in polar and nonpolar solvents to understand its intriguing dual absorption and emission behavior. Steady-state and time-resolved fluorescence studies clearly indicate that the short wavelength emission band of ACAN arises from the higher excited singlet state, S2, while the longer wavelength emission band arises from the intramolecular charge transfer (ICT) state, S1. Interestingly, both these states can be populated by direct excitation from the ground state. Temperature dependent studies reveal a pronounced activation controlled nonradiative decay channel for the ICT state of ACAN. It is proposed that this activation controlled nonradiative de-excitation arises because of a large relative displacement and a cross-over of the potential energy (PE) surfaces of ACAN in the ground and the ICT states, as a result of different twist angles of the amino group in these two states. Qualitative PE diagrams have accordingly been presented to correlate and rationalize the observed results. The present study also brings to light the interesting excited state prototropic behavior of ACAN and the consequent modulation of the ICT emission that has not been reported in the literature so far.

“…However, many contributions to elucidating the viability of these structural models have been experimentally derived from both external [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and internal factors of the DMABN molecule, [31][32][33][34][35][36][37][38][39][40][41] and theoretical data obtained with the most sophisticated computational methods. [42][43][44][45][46][47][48][49][50][51][52][53][54] Also, this topic has been the subject of several reviews. [55][56][57][58][59] Out of these extensive readings some points of great importance towards understanding the photophysics of DMABN have been incorrectly examined, and even some assumptions are taken for granted.…”

Section: Introductionmentioning

confidence: 99%

On the dual emission of p-dimethylaminobenzonitrile and its photophysical implications

Catalán

2013

A solvatochromic analysis of available absorption and LE and TICT emission data in p-dimethylaminobenzonitrile (DMABN) was conducted. Applying the Abe method to the results of a thermochromic analysis of DMABN in 1-chlorobutane (ClB) allowed us to determine the polarizability and dipole moment of the excited electronic states involved in the absorption and emission transitions. As shown herein, the LE → TICT excited state reaction for DMABN is triggered by the solvent polarity but is additionally influenced by the viscosity. The experimental evidence negates the assumption that the radiative constant for the TICT fluorescence of DMABN is temperature-dependent.