Photoinduced Intramolecular Charge Transfer in 9-Aminoacridinium Derivatives Assisted by Intramolecular H-Bond

Abstract

Fluorochromic dyes derived from 9-aminoacridinium containing a vinylene function with electron withdrawing groups such as diethyl [(acridinium-9-ylamino)methylene]malonate (I), ethyl [(acridinium-9-ylamino)methylene]cyanoacetate (II), [(acridinium-9-ylamino)methylene]malononitrile (III), are prepared and studied in their monoprotonated form. Absorption spectra of the new dyes are red shifted compared to that of the precursor dye. The observed dual fluorescence and multiexponential decay are ascribed to normal emission from the acridinium chromophore in addition to excited-state intramolecular charge transfer (ESICT) process. However, biexponential decay character is observed only for the dicyano derivative (compound III), whereas for the two other systems, more complex kinetics and a three-component decay is recovered. The analysis of the fluorescence decays in different solvents for the first two compounds reveals two short-lived components in the range of 160-350 ps and 1.1-3.0 ns, related to formation and decay of the ESICT state, plus a third one with decay time of about 9 ns, which is ascribed to the normal emission from the acridinium chromophore as an enol tautomer or as an intramolecular H-bond conformer (closed form tautomer). For the dicyano derivative, in which the absence of carbonyl group precludes the H-bond interaction, the biexponential fitting reveals a slightly fast formation rate of the ESICT state with values on the order of 10(10) s(-1), whereas its decay time is between 0.6 and 3.2 ns, depending on the solvent used.

Ground‐ and Excited‐State Hydrogen Bonding in the Diazaromatic Betacarboline Derivatives

“…Reprinted with permission from [58]. order of magnitude to those reported for the ICT states of other compounds, such as 9-aminoacridinium derivatives and N-phenylpyrrole [68,69]. Interestingly, t 0 ICT is also in excellent agreement with the values reported by different authors for the decay time of the zwitterionic phototautomer of betacarboline [22,28,50].…”

Time resolved emission spectroscopy of poly(2,5-dicyano-p-phenylene-vinylene) films

“…The laser pulsed frequency was reduced by using a Conoptics pulse picker system. 16 Before spectral measurements, the films over the glass plate were rinsed with acetonitrile and dried at low pressure. The film samples were then kept in a low-pressure optical compartment to avoid the oxygen quenching and oxidation effects, and were disposed in front-face configuration at room temperature (20 ºC).…”

Investigation of contrasting hydrogen bonding pattern of 3-(phenylamino)-cyclohexen-1-one with solvents in the ground and excited states

“…As the formation of intramolecular charge transfer (ICT) state is not considered within the theory of general solvent effects [4], we limit our analysis of solvatochromic shift of the locally excited (LE) species only. It has been reported in literature that Lippert-Mataga analysis provides a reliable means to examine the specific solvent effect on the photophysics of a probe molecule qualitatively [4,36,37]. To derive the Lippert-Mataga equation it was approximated that the energy difference between the ground and excites states of a molecule is dependent on the refractive index (n) and dielectric constant (e) of the solvent and the equation has been expressed mathematically as [4] …”