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Intramolecular charge transfer of 4-(dimethylamino)benzonitrile probed by time-resolved fluorescence and transient absorption: No evidence for two ICT states and a reaction intermediate
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10.1063/1.3270165
/content/aip/journal/jcp/131/22/10.1063/1.3270165
http://aip.metastore.ingenta.com/content/aip/journal/jcp/131/22/10.1063/1.3270165

Figures

Image of FIG. 1.
FIG. 1.

Fluorescence and absorption spectra of DMABN in acetonitrile (MeCN) at . The molar extinction coefficient is indicated on the right hand axis. The fluorescence spectrum of DMABN in MeCN is separated into its LE and ICT components, by using the LE fluorescence spectrum of 4-(methylamino)benzonitrile (MABN). The arrows indicate the excitation wavelength (272 nm) and the emission wavelengths for the decays listed in Table I.

Image of FIG. 2.
FIG. 2.

Fluorescence decays of deaerated solutions of DMABN in MeCN at [Eqs. (1)–(4)]. (a) LE decay (350 nm) for a fresh solution, with , , and [Eq. (3)]. (b) ICT decay (520 nm) for a fresh solution [similar to (a)], with , , and [Eq. (4)]. (c) LE decay (350 nm) for a solution after prolonged irradiation, with , , and . (d) ICT decay (520 nm) for a solution after prolonged irradiation [similar to (c)], with , , and . The shortest decay time is listed first. The weighted deviations sigma, the autocorrelation functions A–C and the values for are also indicated. Excitation wavelength: 272 nm. Time resolution: 0.496 ps/channel with a time window of 1200 effective channels.

Image of FIG. 3.
FIG. 3.

The nanosecond fluorescence decay times at 350 nm and at 520 nm of deaerated DMABN in MeCN at as a function of the LE amplitude ratio [Eq. (3)]. The rectangular data points come from Ref. 23. The variation in has been achieved by increasing the duration of the laser irradiation, which leads to photochemical degradation of DMABN, see text.

Image of FIG. 4.
FIG. 4.

Fluorescence response functions of DMABN in acetonitrile/MeCN at with 10.04 ps/channel in 1900 channels. (a) Global analysis of the LE decay (b) and the ICT response function (c), giving . (b) LE decay, . (c) ICT fluorescence response function, , see Eqs. (1)–(4) and text.

Image of FIG. 5.
FIG. 5.

Global analysis of simulated LE and ICT fluorescence response functions (SPC) of DMABN in MeCN at for two time resolutions: 0.5 ps/channel in 1200 channels [(a) and (b)] and 10 ps/channel in 1900 channels [(c) and (d)]. For all ICT response functions, the simulation was made with and with [Eqs. (2) and (4)]. The LE decays in (a) and (c) have the same decay times and , with [Eqs. (1) and (3)]. To show the influence of shortening of on the global analysis, and in (b) and and in (d) were used in the simulations. These values represent the shortest times at which a problematic LE residuals and autocorrelation functions (A–C) become clearly visible at the two time scales. See caption of Fig. 2.

Image of FIG. 6.
FIG. 6.

ESA spectra at two pump-probe delay times of DMABN, MMD, and MMF in -hexane at . A correction for stimulated emission has been applied.

Image of FIG. 7.
FIG. 7.

ESA spectra at two pump-probe delay times of (a) MMD, (b) MMF, (c) MMBr, (d) , and MME in acetonitrile (MeCN) at . A correction for stimulated emission has been applied.

Tables

Generic image for table
Table I.

Fluorescence decay times and and amplitude ratios (LE) and (ICT) [Eqs. (1)–(4)] for DMABN in acetonitrile at , from SPC experiments, measured at different emission wavelengths. See text and Fig. 1.

Generic image for table
Table II.

Fluorescence decay times and , amplitude ratios (LE) and (ICT) [Eqs. (1)–(4)], forward and backward ICT rate constants and and the ICT lifetime (scheme 2) derived from a global analyis of artifical LE and ICT fluorescence response functions at two time resolutions (0.496 and 10.04 ps/channel), see Fig. 5. The value of used as input in the global analysis is listed. The other input data are kept fixed: , , , and . These data are modeled on DMABN in acetonitrile at (Ref. 23).For the calculation of , , and from , , and , of the model compound MABN (no ICT) is employed.

Generic image for table
Table III.

Decay times and and LE amplitude ratio [Eq. (3)] for DMABN in acetonitrile (data for each section in the order of publication, starting with the latest).

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/content/aip/journal/jcp/131/22/10.1063/1.3270165
2009-12-10
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Intramolecular charge transfer of 4-(dimethylamino)benzonitrile probed by time-resolved fluorescence and transient absorption: No evidence for two ICT states and a πσ∗ reaction intermediate
http://aip.metastore.ingenta.com/content/aip/journal/jcp/131/22/10.1063/1.3270165
10.1063/1.3270165
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