First and second derivative analysis of electroabsorption spectra in conjugated molecules and polymers: Stark shift and Stark broadening

Kulakov, T. A.; Paraschuk, Dmitry Yu.

doi:10.1016/s0009-2614(00)00667-9

Cited by 7 publications

(9 citation statements)

References 19 publications

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“…A similar feature for the centrosymmetric system has been pointed out on the film sample of polyacetylene and polydiacetylene and has been interpreted as a linear Stark shift due to Δμ arising from disorder-induced asymmetry of polymer segments . On the other hand, it is noteworthy that the second-derivative profile can emerge even for an ideally symmetric system (Δμ = 0) via the Δα mechanism, if the energy gap between strongly coupled dipole-allowed and dipole-forbidden excited states is comparable with their line widths, i.e., “the quadratic Stark broadening”. , In this paper, we show that this condition is nearly satisfied by Z n as a result of the accidental degeneracy of the B x and CT states.…”

Section: Introductionsupporting

confidence: 66%

“…The EA profile associated with the quadratic Stark shift strongly depends on the energy gap Δ between relevant excited states (here, the B x and CT 0 states) relative to their line widths Γ: a purely first-derivative profile emerges when Δ ≫ Γ while the contribution of second-derivative nature increases along with decreasing Δ, and the line shape becomes essentially second derivative when Δ ≤ Γ. , Although Δ = 0.32 eV for the B x and CT 0 states is larger than their line widths of 0.09 eV, we note the rather enhanced second-derivative nature for the channel 1 spectrum as compared with the EA spectrum of Z1 . It is also noteworthy that the field-induced absorption by the CT 0 state is quite significant in the present system since this state is coupled with two nearby dipole-allowed states (B x and CT x ) as represented by the channel 2 spectrum.…”

Section: Resultsmentioning

confidence: 78%

“…However, it is also noteworthy that both Q(1,0) and B x bands become sharper along with an increasing number of porphyrin units , consistent with the view of the electronic transitions of porphyrin J -aggregates. The EA intensity depends on the line width, Γ, with Γ -2 scaling of features due to the quadratic Stark shift (first-derivative profile) and Γ -3 scaling for the quadratic Stark broadening (second-derivative profile). , Taking account of such strong line width dependence, it is likely that the motional narrowing of the B x band is predominant in providing the above-mentioned feature of the EA spectra of porphyrin arrays.…”

Section: Resultsmentioning

confidence: 99%

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Quantum-Chemical Investigation of the Electroabsorption Spectra of Directly Meso−Meso-Linked Porphyrin Arrays: Essential Role of Charge-Transfer Excited States Accidentally Overlapping with Soret Bands

Matsuzaki

Nogami

Iwaki³

et al. 2005

J. Phys. Chem. A

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The electroabsorption (EA) spectra of directly meso-meso-linked porphyrin arrays (Zn, n = 1-3) have been investigated by means of the sum-over-states (SOS) approach at the INDO/S-SCI level theory. The experimental EA spectra of Zn (n > or = 2) exhibit an unusual second-derivative line shape at the exciton split low-energy B(x) band in contrast to the first-derivative spectrum of Z1, which is readily ascribed to a quadratic Stark shift of the B (Soret) band. Although the second-derivative line shape is usually attributed to a difference in the permanent dipole moment (Deltamu) between the ground and excited states, it should be vanishing for Zn due to their essentially D(2)(d) or D(2)(h) symmetry. As pointed out in our previous studies, the interporphyrinic charge-transfer (CT) excited states are accidentally overlapping with the excitonic B bands and the present calculations reveal that the B(x) state is strongly coupled via a transition dipole moment with two such CT states. These situations give rise to a quadratic Stark effect on the B(x) band that is intermediate between Stark shift (first derivative) and Stark broadening (second derivative), and play a central role in establishing the anomalous second derivative nature of the EA spectrum. Moreover, based on the comparison between the theoretical and experimental spectra, there must be an additional factor that further enhances the second derivative nature of the EA spectrum of porphyrin arrays. Discussions on this issue including the preliminary investigations on the role of solvent (PMMA)-induced asymmetry are also presented.

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Section: Introductionsupporting

confidence: 66%

Section: Resultsmentioning

confidence: 78%

Section: Resultsmentioning

confidence: 99%

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Quantum-Chemical Investigation of the Electroabsorption Spectra of Directly Meso−Meso-Linked Porphyrin Arrays: Essential Role of Charge-Transfer Excited States Accidentally Overlapping with Soret Bands

Matsuzaki

Nogami

Iwaki³

et al. 2005

J. Phys. Chem. A

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“…At even higher energies the EA spectrum shows a modulation spectral feature that resembles a second derivative with zero crossing at 3.6 eV and 3.8 eV, respectively, these are therefore ascribed to the excited states mA g and nB u ͑the latter symbolizes the continuum band threshold in PCPs͒ that mix under the influence of the electric field; similar to EA spectra in other PCPs. 35 Also above E͑nB u ͒ there is another field-induced absorption band at ϳ3.9 eV that, similar as in other PCPs we assigned it as due to an even state at higher energies, 26,36 namely, the kA g .…”

Section: B Electroabsorption Spectroscopysupporting

confidence: 77%

Nonlinear optical spectroscopy of excited states in disubstituted polyacetylene

2010

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We used a variety of nonlinear optical ͑NLO͒ spectroscopies for studying the excited states order and primary photoexcitations in disubstituted polyacetylene ͑DPA͒. The NLO spectroscopies include ultrafast pump-probe photomodulation in a broad spectral range of 0.2-2.5 eV, two-photon absorption in the range of 3.2-4.2 eV, and electroabsorption ͑EA͒ in the range of 2.3-4.1 eV. For completeness we also measured the linear-absorption and photoluminescence spectra. We found that the primary photoexcitations in DPA are singlet excitons with three photoinduced absorption ͑PA͒ bands, PA 0 at 0.6 eV, PA 1 at 1 eV, and PA 2 at 1.6 eV, respectively, and a stimulated emission band at ϳ2.5 eV. This is in contrast to other -conjugated polymers where the singlet excitons are characterized by two PA bands and a stimulated emission ͑SE͒ band. We conclude that in addition to the four essential excited states known to determine the NLO spectra of -conjugated polymers, namely, 1A g , 1B u , mA g , and nB u ; in DPA there is another important complex of states at ϳ3.3 eV that contains almost degenerate states with odd and even parity symmetries ͑dubbed here transverse excited state or TES͒ that is probably reminiscent of the 2A g state in unsubstituted trans-polyacetylene, which lies in between the 1B u and mA g of which dipole moment has a strong component perpendicular to the chain direction. In support for this model we found that the depolarization ratio of the EA spectrum drastically changes around the TES from a value of ϳ2 for ប Ͻ 3 eV to ϳ0.5 for ប Ͼ 3.3 eV.

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“…3,13,14 In this context it has been realized early that being limited to well-isolated electronic absorptions, the Liptay approach becomes dangerous if forbidden (dark) states are not far in energy with respect to apparently well isolated linear absorption bands. [15][16][17][18][19] Specifically, pseudo second-derivative contributions to the EA spectra can arise from the mixing of allowed and forbidden states induced by the electric-field. As a result, spurious large ∆µ values may be estimated via a fit of EA spectraà la Liptay.…”

Section: Introductionmentioning

confidence: 99%

Electroabsorption spectra of multipolar chromophores

2008

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Electroabsorption (EA) spectroscopy is a useful tool to investigate electronic properties of solvated dyes. Following Liptay, EA spectra can be fitted from the linear absorption spectrum and its first and second derivatives, to extract the variation of the dipole moment and of the molecular polarizability upon photoexcitation. In the lack of specific models, the Liptay approach, developed for dipolar dyes, is currently applied to multipolar dyes. We discuss EA spectra of quadrupolar and octupolar dyes, based on essential state models. A perturbative treatment of the applied field allows to express the numerically exact EA spectra of multipolar dyes: the second-derivative contribution vanishes for quadrupolar dyes, and for both quadrupolar and octupolar dyes a contribution appears due to the electric field-induced absorption to a dark (two-photon allowed) state. A new fitting procedure is then proposed for EA spectra of quadrupolar and octupolar chromophores, leading to reliable estimates of the molecular parameters. The method is applied to a few dyes of interest for two-photon absorption applications.

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First and second derivative analysis of electroabsorption spectra in conjugated molecules and polymers: Stark shift and Stark broadening

Cited by 7 publications

References 19 publications

Quantum-Chemical Investigation of the Electroabsorption Spectra of Directly Meso−Meso-Linked Porphyrin Arrays: Essential Role of Charge-Transfer Excited States Accidentally Overlapping with Soret Bands

Quantum-Chemical Investigation of the Electroabsorption Spectra of Directly Meso−Meso-Linked Porphyrin Arrays: Essential Role of Charge-Transfer Excited States Accidentally Overlapping with Soret Bands

Nonlinear optical spectroscopy of excited states in disubstituted polyacetylene

Electroabsorption spectra of multipolar chromophores

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