Excited‐state intramolecular charge transfer in donor/acceptor‐substituted aromatic hydrocarbons and in biaryls. The significance of the redox potentials of the D/A subsystems

Abstract

Abstract. The energy of the charge transfer (CT) emission maximum of a series of dual fluorescent 4-aminobenzonitriles in diethyl ether and acetonitrile does not show a correlation with the redox potentials of the amino (D) and benzonitrile (A) subgroups. It is therefore concluded that these electron donor and acceptor subgroups cannot be treated in the same way as the A and D molecules in exciplexes '(A-D'). This means that in the intramolecular charge transfer (ICT) state of the aminobenzonitriles, a considerable electronic coupling between the A -and D + parts exists, in contradiction with the twisted intramolecular charge transfer (TICT) hypothesis. For 9,9'-bianthryl, lO-cyan0-9,9'-bianthryl and 10,10'-dicyano-9,9'-bianthryl, photostationary and timeresolved measurements are presented, which show that the influence of the cyano substituents on the ICT reaction in the excited state can be understood by considering the redox potentials of the anthryl groups. The introduction of an additional cyano group in an aminobenzonitrile, however, leads to the disappearance of ICT and dual fluorescence, indicating that the photophysics of these molecules cannot be understood on the basis of the redox potentials of the D and A constituents.

Fluorescence characteristics of 5-carboxytetramethylrhodamine linked covalently to the 5' end of oligonucleotides: multiple conformers of single-stranded and double-stranded dye-DNA complexes

“…The hypothesis of TICT states has recently been challenged (Zachariasse et al, 1993;von der Haar et al, 1995); because these arguments are based on experiments with compounds that have been central to the TICT hypothesis (4-aminobenzonitriles), they might be expected to carry over to the case of rhodamines (K. A. Zachariasse, personal communication). The rhodamines and 4-aminobenzonitriles are similar in many respects.…”

Spectral Signature of 2-[4-(Dimethylamino)styryl]-1-methylquinolinium Iodide: A Case of Negative Solvatochromism in Water

“…Different models like pseudo-JahnÀTeller interaction of excited states 3,4 and in-plane bending and rehybridization of acceptor 5,6 were proposed for the dual emission of DMABN, but the most accepted one is twisted intramolecular charge transfer (TICT), where a π/2 twist of the donor moiety with respect to the benzene plane is considered to stabilize the ICT state. 7À9 As these types of ICT systems are very sensitive to solvent polarity and viscosity, much research 10,11 is being done to understand and systematize the ICT systems.…”

The configuration, solvatochromism and metallo‐responses of two novel cyano‐containing oligo(phenylene‐vinylene) derivatives

“…3, the fluorescence decay time of OPVCN–C12 in chloroform solution (20°C, τ 1 = 1.47 ns) can be fitted as single exponentials without indication of a locally excited (LE) state. The result demonstrated that an ICT reaction from an LE state to an ICT state probably occurred in the solution (34,35). The decay time of OPVCN–C12 in a mixture of dichloromethane–acetonitrile (v/v, 1:3) solution ( τ 1 = 0.36 ns, single exponentials) was much shorter than that in pure chloroform solution, which indicated the existence of unstable excited states and stronger intramolecular charge transfer process in OPVCN–C12 in a dichloromethane–acetonitrile (v/v, 1:3) solution.…”