Trans-cis photoisomerization mechanism of carbocyanines: experimental check of theoretical models

Ponterini, Glauco; Momicchioli, Fabio

doi:10.1016/0301-0104(91)80011-6

Cited by 96 publications

(126 citation statements)

References 25 publications

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“…The polymethine proton resonances are reported in the following form: In conformational studies, couplings of 3 J HH = 13 Hz have previously been reported to indicate quasi-planar all-trans cyanine structures. [74][75][76] The proton chemical shifts are qualitatively consistent with the charge alternation expected for polymethines. 40,41 All three samples contained impurities (or minor forms with millisecond lifetimes) below the 2% level.…”

Section: Methodssupporting

confidence: 76%

Solvatochromism and Solvation Dynamics of Structurally Related Cyanine Dyes

et al. 2002

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Absorption, fluorescence, and magic-angle pump-probe experiments characterize the solvatochromism and relaxation dynamics of three structurally related near-infrared tricarbocyanine dyes (HDITCP, IR125, and IR144) in solution. Agreement with solvatochromic theory is found in solvents where the conductivity approximately matches that predicted for complete ionic dissociation. The nonpolar solvatochromism of HDITCP and IR125 allows the polar solvatochromism of the IR144 absorption spectrum to be attributed to a specific functional group. Resonance structure arguments predict a dipole moment decrease upon electronic absorption by IR144, consistent with the observed solvatochromism. Assuming a point dipole, spherical cavity reaction field model, self-consistent feedback between the solvent and the polarizable IR144 solute accounts for 1/2 to 1/3 of the observed polar solvent shifts. A geometry change in the excited state leads to nearly nonpolar solvatochromism in the IR144 emission spectrum. Femtosecond magic-angle pump-probe transients show similar underdamped intramolecular vibrational quantum beats in all three molecules, but find solventdependent overdamped responses on a picosecond time scale in all three dyes. The quantum beat decays determine inhomogeneous vibrational dephasing times of a few picoseconds. Vibrational relaxation, nonpolar solvation, and dielectric relaxation all take place on similar time scales, but the picosecond relaxations are all slower and of larger amplitude for IR144 (polar solvatochromism) than HDITCP (nonpolar solvatochromism). In contrast to HDITCP, IR144 has a prominent solvent-dependent "coherence spike" near T ) 0 which is attributed to femtosecond polar solvation dynamics.

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Section: Methodssupporting

confidence: 76%

Solvatochromism and Solvation Dynamics of Structurally Related Cyanine Dyes

et al. 2002

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“…The right side of Figure 5 illustrates the corresponding process, in which torsion about the 8,9 bond leads to the t conical intersection, which couples to a region of the S 0 surface where either the 8,9-cis isomer or the trans isomer is formed. The presence of torsional barriers on the S 1 surface is consistent with the temperature dependence of the quantum yield for trans → cis isomerization, which is 0.070 at 190 K and 0.250 at 293 K. 26 It has been proposed that the 2,8-cis isomer is the main photoisomer for DTC + on the basis of calculated absorption cross sections and transition energies 14 and NMR spectra of cooled, irradiated samples. 13 For isolated trans-DTC + ions, the barriers for 2,8 and 8,9 torsions in the S 1 state, have been calculated using the CI-INDO method as 13 and 10 kJ/mol, respectively, 27 presumably sufficiently high to prohibit access to the twisted states (t′ and t) and confine the system to the trans Franck−Condon region, at least at the prevailing effective temperature in the drift section of the apparatus (340 K).…”

Section: Resultsmentioning

confidence: 75%

Photoisomerization Action Spectroscopy of the Carbocyanine Dye DTC⁺ in the Gas Phase

et al. 2013

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Molecular photoisomerization plays a crucial role in diverse biological and technological contexts. Here, we combine ion mobility spectrometry and laser spectroscopy to characterize the photoisomerization of molecular cations in the gas phase. The target molecular ions, polymethine dye cations 3,3'-diethylthiacarbocyanine (DTC(+)), are propelled through helium buffer gas by an electric field and are photoisomerized by light from a tunable laser. Photoexcitation over the 450-570 nm range converts trans-DTC(+) to cis-DTC(+), noticeably modifying the ions' arrival time distribution. The photoisomerization action spectrum, which has a maximum at 535 nm, resembles the absorption spectrum of DTC(+) in solution but is shifted 25 nm to shorter wavelength. Comparisons between measured and calculated mobilities suggest that the photoisomer involves a twist about the second C-C bond in the methine chain (8,9-cis isomer) rather than a twist about the first methine C-C bond (2,8-cis isomer). It is postulated that the excited gas-phase ions internally convert from the S1 Franck-Condon region to the S0 manifold and explore the conformational landscape as they cool through He buffer gas collisions. Master equation simulations of the relaxation process in the S0 manifold suggest that the 8,9-cis isomer is preferred over the 2,8-cis isomer because it lies lower in energy and because it is separated from the trans isomer by a substantially higher barrier. The study demonstrates that the photoisomerization of molecular ions can be probed selectively in the gas phase, providing insights into photoisomerization mechanisms and information on the solvent-free absorption spectrum.

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“…G ) p 21 + f 21 p 21 + 1/B 21 (10) another species in the photophysical processes, in addition to N and P1. This means that a two-photoisomer model is needed under high fluences.…”

Section: Resultsmentioning

confidence: 98%

Kinetic Analysis of a Double Photoisomerization of the DTDCI Cyanine Dye

1996

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Simultaneous laser absorption spectroscopy and laser induced fluorescence under steady-state conditions, together with analysis of fluorescence spectra at various excitation conditions, have been carried out to elucidate the photoisomerization processes of 3,3′-diethylthiadicarbocyanine iodide (DTDCI) in methanol solution. The data were obtained by varying the laser fluence at several wavelengths, and fits were performed considering two kinetic models, involving two or three isomers. The results point to the formation of a second photoisomer under high excitation fluences. Its absorption spectrum is shifted toward longer wavelengths with respect to the spectra corresponding to the normal species and the first photoisomer, which are strongly overlapped. Changes in the fluorescence spectra with the excitation fluence, appearing in the DTDCI lasing region, are attributed to the second photoisomer emission. Values are obtained for the photoisomerization and backphotoisomerization quantum yields, as well as for the thermal ground-state back-isomerization yield and ground state absorption cross sections at several wavelengths for both photoisomers. IntroductionThe photoisomerization dynamics of polymethine cyanine dyes has been extensively considered from both the theoretical and experimental points of view. The formation of photoisomers has been analyzed through different experimental techniques such as flash photolysis, fluorescence, picosecond timeresolved spectroscopy, optoacoustic techniques, and others. 1-6 Rulliere's model for two isomeric species, corresponding to the normal conformer and to the photoisomer, is the most widely used model to explain the photophysical behavior of these kinds of molecules. Good agreement has been found between this model and the experimental results with several cyanine dyes such as 3,3′-diethyloxadicarbocyanine iodide (DODCI), 3,3′-diethylthiacarbocyanine iodide (DTCI), 3,3′-diethyloxacarbocyanine iodide (DOCI), merocyanine 540, and some others. On the basis of this model, the photophysical processes in these carbocyanines are thought to be well-understood, and the kinetic and spectroscopic parameters are well-known. [7][8][9][10][11][12][13][14][15][16][17] However, the above-mentioned model does not provide an adequate explanation for the photoisomerization process in all cyanines. 3,3′-Diethylthiadicarbocyanine iodide (DTDCI, Chart 1) is an example of this statement, since authors have investigated the photoisomerization mechanisms and photophysical and spectroscopic properties of DTDCI for more than 20 years, obtaining controversial results. 18-25 DTDCI is used as a laser dye for pulsed systems in the 700-760 nm region and as a saturable absorber in passive "mode-locking" techniques, when used with cresyl violet and Rhodamine 101 lasers. 26-29 Like other cyanines dyes, DTDCI shows very strong absorption in the visible and near-UV regions and presents a reversible photoisomerization process.The first evidence of a photoisomer (P1) in ethanol solutions of DTDCI was reported by ...

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Trans-cis photoisomerization mechanism of carbocyanines: experimental check of theoretical models

Cited by 96 publications

References 25 publications

Solvatochromism and Solvation Dynamics of Structurally Related Cyanine Dyes

Solvatochromism and Solvation Dynamics of Structurally Related Cyanine Dyes

Photoisomerization Action Spectroscopy of the Carbocyanine Dye DTC⁺ in the Gas Phase

Kinetic Analysis of a Double Photoisomerization of the DTDCI Cyanine Dye

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Trans-cis photoisomerization mechanism of carbocyanines: experimental check of theoretical models

Cited by 96 publications

References 25 publications

Solvatochromism and Solvation Dynamics of Structurally Related Cyanine Dyes

Solvatochromism and Solvation Dynamics of Structurally Related Cyanine Dyes

Photoisomerization Action Spectroscopy of the Carbocyanine Dye DTC+ in the Gas Phase

Kinetic Analysis of a Double Photoisomerization of the DTDCI Cyanine Dye

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Photoisomerization Action Spectroscopy of the Carbocyanine Dye DTC⁺ in the Gas Phase