Radiative Depopulation of the Excited Intramolecular Charge-Transfer State of 9-(4-(N,N-Dimethylamino)phenyl)phenanthrene

Abstract

Intramolecular photoinduced electron transfer in 9-(p-N,N-dimethylanilino)phenanthrene (9DPhen) has been studied in solution. The solvent dependence of the fluorescence spectra of 9DPhen indicates that the emission occurs from a highly polar excited state. The quantum yield of fluorescence (Φ f ) of 9DPhen is quite high and increases with increasing solvent polarity. The radiative rate constant (k f ), however, shows a maximum for solvents of intermediate polarity, e.g., in butyl acetate a value of 2.3 × 10 8 s -1 is attained. These results are difficult to explain within the "TICT" (twisted intramolecular charge transfer) model, which predicts a strongly forbidden fluorescence caused by a minimum overlap of the orbitals involved in the transition. The above-mentioned trend as a function of the solvent polarity is observed in particular donor-acceptor substituted arenes where the L b state of the corresponding arenes is lower in energy than the L a state. The quantum chemical calculations actually could explain this behavior on the basis of an ICT state which interacts with the lower lying 1 L a and 1 L b states of the acceptor. The quantum mechanical mixing of states can occur by two pathways, namely orbital mixing and mixing of configurations, and is modified by geometrical changes and by solvent polarity. The single exponential fluorescence decay, obtained with time-correlated single-photon-timing, suggests emission from an excited charge-transfer state, resulting from a solvent-induced rapid relaxation of the initial delocalized excited state of 9DPhen, obtained immediately after picosecond pulsed excitation. Picosecond transient absorption spectra in acetonitrile show a rapid decay within a few picoseconds from a less polar but delocalized excited state toward a more polar ICT state. Even the triplet state of 9DPhen in isopentane at 77 K shows a significant polar character. As a reference compound, 9-phenylphenanthrene (9PhPhen) was also examined by means of stationary and time-resolved fluorescence measurements as well as transient absorption experiments.

Synthesis and thermo-responsive behavior of fluorescent labeled microgel particles based on poly(N-isopropylacrylamide) and its related polymers

“…A fluorescent probe monomer VDP and a VDP unit model compound EtDP were the same used in the literatures [13,14]. VDP was synthesized by the Wittig reaction of 3-acetyl-9-(4-N,Ndimethylaminophenyl)phenanthrene, which was obtained by the Grignard coupling reaction of 3-acetyl-9-bromophenanthrene and (4-(N,N-dimethylamino)phenyl)magnesium bromide similar to the DP synthesis [18], with methyltriphenylphosphonium bromide and n-butyllithium in dry THF. A VDP unit model compound 3-ethyl-9-(4-N,Ndimethylaminophenyl)phenanthrene (EtDP)(chemical structure is shown in Fig.…”

“…One of the fluorescent probes that we have used is 9-(4-N,N-dimethylaminophenyl)phenanthrene (DMA-Phen: DP) in which an electron donor N,N-dimethylaniline (DMA) and an electron acceptor phenanthrene (Phen) are linked directly with a single bond. DP shows an intense and structureless intramolecular charge-transfer (ICT) fluorescence and its fluorescence emits a strong solvatochromism [18][19][20]. It could be possible to investigate the thermo-responsive behavior and the microenvironments of the microgel particles by monitoring the fluorescence from the DP units linked to those.…”

Intramolecular Charge Transfer in Pyrromethene Laser Dyes: Photophysical Behaviour of PM650

“…The corresponding rate constant (k ict ) should be solvent-dependent, since the stabilisation of the ICT state is strongly favoured in polar media (Scheme 1). [36][37][38][39][40] Taking into account that the fluorescence decay curve of PM650 is analysed as a one-exponential decay in all considered solvents, the reversible process of an electron transfer from the ICT state to the localised S 1 excited state should be negligible.…”

“…The fluorescence from an ICT state is characterised by a large Stokes shift in polar solvents, which reduces the reabsorption/re-emission effects and the losses in the resonator cavity of tunable lasers. Moreover, due to the high sensibility of the photophysical properties of an ICT state to the nature of the solvent, [36][37][38][39][40] dyes that exhibit an ICT state are powerful tools as fluorescence molecular sensors in a multitude of systems, which include biological and chemical systems. [41][42][43] In the present Article, the photophysics of the pyrromethene 650 (PM650) dye is studied.…”

From pirazoloquinolines to annulated azulene dyes: UV–VIS spectroscopy and quantum chemical study

“…so-called charge transfer (CT) states), one may expect a considerable lowering of their energies in polar solvent environment. This may lead basically to the two scenarios: (i) one of the strongly polar excited CT states of the solute becomes in solvent the lowest excited singlet fluorescent state (so-called inversion of states) or (ii) the lowest locally excited weakly polar state appears to be strongly modified due to its mixing with a lowering strongly polar CT state [34,35]. On the other hand, the fluorescent moment M fl exhibits rather weak F-dependence (see Table 1) for all dyes, thus the electronic structure and molecular conformation of the fluorescent excited state should not change substantially if the solvent polarity changes from CHX to ACN.…”