One- and Two-Photon Absorption Spectra

Shown are only the states for which dipole moment difference between a given excited state and the ground state (A/r) is larger than 2.0 D and f 0.05 

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Octatetraene is the shortest unsubstituted polyene that exhibits fluorescence. The X kg —> 2 kg transition is clearly seen in one- and two-photon absorption spectra and the 2 kg is unambiguously identified to be the lowest singlet state1. 

A short mathematical analysis of formulae Eq. 13 and Eq. 14 shows that the absorptions corresponding to p = 1 and p = 1 are highly dominating the one-and two-photon absorption spectra. 

Fig. 36 Experimental one- and two-photon absorption spectra of 9,9 -dihexylfluorene oligomers in dichloromethane. Top Absorption coefficient per monomer. Bottom Two-photon absorption cross-section per monomer. Nx indicates an oligomer containing x monomeric units...

The different dependence on orbital symmetries makes two-photon spectroscopy a useful technique for studying some excited states that are not readily accessible by one-photon excitation. Birge [87] used two-photon excitation to explore the 2 A excited state of retinyl derivatives (Box 4.12) in solution and bound to rhodopsin. Excitation to this state from the ground state is, to a first approximation, forbidden in a one-photon transition but is allowed as a two-photon transition. Comparisons of the one- and two-photon absorption spectra of the unprotonated Schiff base of all-frans-retinal in solution showed that the 2 A state lies below I B. Protonating the Schiff base moves 1 down in energy and inverts the order. In rhodopsin containing a locked 11-cis-retinyl derivative that was unable to undergo photoisomerization, 1 B+ was found to lie below 2 A, in accord with other indications that the Schiff base is protonated [87, 90]. 

This section is organized as follows. Firstly, we shall discuss the structure of the investigated systems (Sect. 3.2.1). The electronic contributions to polarizability, first- and second-order hyperpolarizability are presented in Sect. 3.2.2. In the next section we analyze one- and two-photon absorption spectra of investigated molecules (Sect. 3.2.3), while the discussion of vibrational contributions is given in Sect. 3.2.4. 

The photoelectronic properties of poly(dihexylgermane) were investigated by photoluminescence spectroscopy, after one- and two-photon absorption. The spectra were compared with those of the analogous poly(dihexylsilane)111. 

Simulations of the experimental signal were performed using Equation 1 without adjustable parameters. The spectrum of the pulse and the absorption spectrum of HPTS were measured experimentally. An examination of the molecular structure of HPTS shows that it has no center of symmetry. Since parity restrictions may be relaxed in this case, the similarity between one-photon and two-photon absorption spectra is expected. The spectral phase

phase mask was the same used for the simulations. Both experimental and theoretical data were normalized such that the signal intensity is unity and the background observed is zero. The experimental data (dots) generally agree with the calculated response (continuous line) of the dyes in all pH environments (see Fig. 2). 

Time-dependent density functional theory studies of the photoswitching of the two-photon absorption spectra in stilbenes were reported [15]. The one- and two-photon absorption characteristics of the open- and closed-ring isomers of 1-3 have been... 

S.3.2.4 Practical Example One- and Two-Photon Spectra for R3MCP In this section, we report the 5i So and S2 <— So one- and two-photon absorption, and circular dichroism (CD) spectra of R3MCP, computed according to the FCHTlAH and FCHTIVG models. 

Figure 7-18. (a) One- and two-photon (line and symbols, respectively) absorption spectra of P3BT. (b) EA spectrum of P3BT... 

All physical properties of pyrylium salts (unsubstituted or substituted with alkyl and/or aryl groups) prove the aromaticity of these cations vibrational spectra [66], mass-spectral fragmentations [67], magnetic properties [68-70], and electronic absorption spectra [71]. It should be mentioned that there is a close similarity between the electronic absorption bands of pyrylium salts and those of benzene, easily recognized by the marked bathochromic effect of substituents in y-position of pyrylium salts on one of these bands. Two-photon absorption spectra of 2,4,6-triarylpyrylium cations [72] may be used in optical data storage, lasing, and photodynamic therapy. 

Petek H, Bell AJ, Choi YS, Yoshihara K, Tounge BA and Christensen RL (1995) One- and two-photon fluorescence excitation spectra of the 2 Ag states of linear tetraenes in free jet expansions. J Chem Phys 102 4726 739 Ramasesha S and Zoos ZG (1984) Correlated states in linear polyenes, radicals, and ions Exact PPP transition moments and spin densities. J Chem Phys 80 3278-3287 Raubach RA and Guzzo AV (1973) Singlet-triplet absorption spectrum of uH-trans-retinal. J Phys Chem 75 983-984 Ricci M, Bradforth SE, Jimenez R and Fleming G (1996) Internal conversion and energy transfer dynamics of spheroidene in solution and in the LH-1 and LH-2 light-harvesting complexes. Chem Phys Lett 259 381-390... 

Figure 11 One-photon absorption, fluorescence, and two-photon excitation spectra of diphen-ylhutadiene in ERA at 77 K. The two-photon excitation spectrum is plotted versus where is the wavelength of the laser excitation (Reproduced by permission from J. Chem. Phys., 1980, 73, 4231).

In addition to the nonresonant NLO properties, one- and two-photon spectra of several of the compounds in Fig. 5.3 were also computed in Ref. [56]. The averaged two-photon absorption cross section for isotropic media in the case of two parallel linearly polarized photons <8° > is... 

Fig. 11.1. (a) The optical-absorption spectra of PPV (solid curve) and MEH-PPV (dashed curve). Reprinted with permission from S. J. Martin, D. D. C. Bradley, P. A. Lane, H. Mellor, and P. L. Burn, Phy. Rev. B 59,15133,1999. Copyright 1999 by the American Physical Society, (b) The optical-absorption (one-photon) spectra of a DOO-PPV film (soUd curve) and two-photon absorption of DOO-PPV in solution (circles). Reprinted with permission from S. Frolov, Z. Bao, M. Wohlgenannt, and Z. V. Vardeny, Phys. Rev. B 65, 205209, 2002. Copyright 2002 by the American Physical Society. The chemical structnres of PPV, MEH-PPV and DOO-PPV are shown in Fig. 11.3. 

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