Two-photon absorption spectra of carotenoids compounds

Abstract

Carotenoids are biosynthetic organic pigments that constitute an important class of one-dimensional p-conjugated organic molecules with enormous potential for application in biophotonic devices. In this context, we studied the degenerate two-photon absorption (2PA) cross-section spectra of two carotenoid compounds (b-carotene and b-apo-8 0 -carotenal) employing the conventional and whitelight-continuum Z-scan techniques and quantum chemistry calculations. Because carotenoids coexist at room temperature as a mixture of isomers, the 2PA spectra reported here are due to samples containing a distribution of isomers, presenting distinct conjugation length and conformation. We show that these compounds present a defined structure on the 2PA spectra, that peaks at 650 nm with an absorption cross-section of approximately 5000 GM, for both compounds. In addition, we observed a 2PA band at 990 nm for b-apo-8 0 -carotenal, which was attributed to a overlapping of 1 1 B u þ -like and 21 Ag --like states, which are strongly one-and two-photon allowed, respectively. Spectroscopic parameters of the electronic transitions to singlet-excited states, which are directly related to photophysical properties of these compounds, were obtained by fitting the 2PA spectra using the sum-over-states approach. The analysis and interpretations of the 2PA spectra of the investigated carotenoids were supported by theoretical predictions of one-and two-photon transitions carried out using the response functions formalism within the density functional theory framework, using the long-range corrected CAM-B3LYP functional.

Benchmarking two-photon absorption cross sections: performance of CC2 and CAM-B3LYP

“…These elements are likely to be inaccurate for TDDFT as well since they crucially depend on the electron density of the excited states, but they are less studied in the literature. To do this in a proper way, one should not only take into account the form of the lineshape function for a particular excitation 32,36,39 (see Section 2.2) and the type of experiment that it is compared to (see Section 2.3), but also temperature effects, 48 non-Condon transitions 64 and the environment. There seems to be a need for benchmarking TDDFT/CAM-B3LYP TPA strengths of a larger set of medium-sized chromophores-including different protonation states-against a more accurate method such as EOM-EE-CCSD in order to obtain a better estimation of the error inherent to using TDDFT/CAM-B3LYP to calculate the TPA strength.…”

“…30,32,36,39 What is usually done, however, is choosing a single empirical parameter for G, often chosen to be 0.1 eV, 13,14,18,21,22,28,29,37,38 but also other broadening factors have been used, usually taken from the broadening of a specific peak in an experimental spectrum. 30,32,36,39 What is usually done, however, is choosing a single empirical parameter for G, often chosen to be 0.1 eV, 13,14,18,21,22,28,29,37,38 but also other broadening factors have been used, usually taken from the broadening of a specific peak in an experimental spectrum.…”

“…19,21 This corresponds to an experimental setup with two laser sources (a so-called doublebeam experiment 41 ), thus in principle allowing for two photons with different energies. [30][31][32][33]39,42,43 In fact, the photon dissipation rate is in this case twice the calculated twophoton absorption rate because two photons together excite the molecule. [30][31][32][33]39,42,43 In fact, the photon dissipation rate is in this case twice the calculated twophoton absorption rate because two photons together excite the molecule.…”

“…[30][31][32][33]39,42,43 In fact, the photon dissipation rate is in this case twice the calculated twophoton absorption rate because two photons together excite the molecule. 31,33,39,42,43 When two lasers are used as the photon sources-as intended in e.g. 31,33,39,42,43 When two lasers are used as the photon sources-as intended in e.g.…”

Relação entre a estrutura molecular e as propriedades de absorção de multi-fótons em compostos orgânicos π-conjugados

“…A contribuição secundaria dos grupos doadores de elétrons é mais acentuada nos retinóides, uma vez que ambos possuem o mesmo comprimento de conjugação e diferentes grupos terminais, o que pode explicar a pequena diferença na magnitude da seção de choque entre os compostos. Além disso, os orbitais moleculares também são uma evidência adicional da quebra efetiva de simetria presente no ATR, ATAR e TβA8C, que explica as transições do tipo dipolares entre os orbitais HOMO → LUMO(123).…”