Electronic and vibronic contributions to two-photon absorption of molecules with multi-branched structures

Abstract

The electronic and vibronic contributions to the two-photon absorption of a series molecules with multi-branched structures have been studied using ab initio response theory. The results indicate that the electronic coupling between different branches alone cannot explain the experimental finding of a strong enhancement of the two-photon absorption cross section over the single branch structure, whereas it is predicted that vibronic contributions can play an important role in this respect. It is shown that for multi-branched molecules the use of circularly polarized light can increase the two-photon absorption cross section by a factor of 1.5 over linearly polarized light excitation.

Localized Emitting State and Energy Transfer Properties of Quadrupolar Chromophores and (Multi)Branched Derivatives

“…25−27 In that case, significant cooperative enhancement of the twophoton cross-section of triple-branched structures could not be observed, in comparison with their counterpart linear moiety. 9,19,20,25 However, considering the short spatial distance between the branches and the identical transition moment of these moieties, it is still not likely that the branches are fully independent of each other. Energy transfer and interactions among the branches in the excited state should still exist within these compounds.…”

Vibronic contributions to resonant NLO responses: two-photon absorption in push–pull chromophores

“…Large effects of e-ph coupling have been recognized within the Condon approximation in TPA spectra of push-pull chromophores 2 , and, within the same approximation, TPA, third harmonic generation (THG) and non-degenerate four-wave mixing spectra of the conjugated polymer polydiacetylene have been shown to be non-trivially affected by e-ph coupling 15 . Recent ab initio calculations of TPA spectra of a few conjugated molecules 5,6 showed sizable and, in some cases even large, Herzberg-Teller (HT) corrections, demonstrating once more the non-trivial role of e-ph coupling in conjugated systems.…”

“…Among other properties, large two-photon absorption (TPA) cross-sections are promising for different applications, ranging from optical storage to biological optical imaging 1 . As a consequence, both experimental and theoretical work [2][3][4][5][6][7] have received strong impetus and several interesting strategies have been proposed to improve NLO responses in general 8,9 and TPA cross-section in particular 1,10 . A presently highly debated topic concerns the importance of vibrational contributions to NLO responses of organic materials [11][12][13][14] .…”

Basis set and electron correlation effects on initial convergence for vibrational nonlinear optical properties of conjugated organic molecules

“…[1][2][3][4][5][6][7][8] Due to the high computational cost, electron correlation has rarely been included in ab initio calculations of the vibrational hyperpolarizability of medium size or large NLO organic molecules. In the few studies available, only the harmonic terms ͑i.e., double harmonic approximation͒ 1,6,9 or the lowest order anharmonic terms ͑i.e., nuclear relaxation contribution, ␤ nr and ␥ nr ) [10][11][12] were computed.…”