Uncovering Structure-Property Relationships in Push-Pull Chromophores: A Promising Route to Large Hyperpolarizability and Two-Photon Absorption

Year: 2020

Authors: Cesaretti A., Foggi P., Fortuna CG., Elisei F., Spalletti A., Carlotti B.

Autors Affiliation: Univ Perugia, Dept Chem Biol & Biotechnol, I-06123 Perugia, Italy; Univ Perugia, Ctr Excellence Innovat Nanostruct Mat CEMIN, I-06123 Perugia, Italy; LENS European Lab Nonlinear Spect, I-50019 Florence, Italy; CNR, Ist Nazl Ott, I-50125 Florence, Italy; Univ Catania, Dept Chem Sci, I-95125 Catania, Italy.

Abstract: In this investigation, we report the first hyperpolarizabilities and two-photon absorption cross sections of a large series of 12 push-pull cationic chromophores. All of these dyes show a dipolar acceptor(+)-pi-donor structure, where the nature of the donor and acceptor units and pi-bridge was synthetically tuned to allow insightful comparisons among the molecules. The hyperpolarizability was obtained through a solvatochromic method, by exploiting the rare negative solvatochromism exhibited by the investigated compounds. The two-photon absorption cross sections were determined through two-photon excited fluorescence measurements by means of a tunable nanosecond laser system for sample excitation. The nonlinear optical properties were discussed relatively to the photoinduced intramolecular charge transfer occurring in these donor-acceptor systems, investigated by femtosecond transient absorption experiments. We found a strong increase in hyperpolarizability upon increasing the molecular conjugation. Unexpectedly, the hyperpolarizability is almost unaffected by an increase in donor/acceptor strength and intramolecular charge transfer degree. Differently, the two-photon absorption cross sections of these dyes are enhanced by an increase in both molecular conjugation and intramolecular charge transfer efficiency. Several recent literature works have reported at the same time scattered information about the hyperpolarizability and two-photon absorption of small organic molecules. Our investigation is, to the best of our knowledge, the first attempt to uncover detailed structure-property relationships for these two nonlinear optical properties. Our results represent a promising route to achieve large hyperpolarizability and two-photon absorption in push-pull dyes and may drive the design of new efficient nonlinear optical materials.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY C

Volume: 124 (29)      Pages from: 15739  to: 1574

More Information: The authors acknowledge support from the Italian “Ministero per lŽUniversita e la Ricerca Scientifica e Tecnologica”, MIUR (Rome, Italy) under the “Dipartimenti di Eccellenza 2018-2022” (grant AMIS) program, and the University of Perugia for the FRB2018 grant. Dr. Maria Antonietta La Serra and Leonardo Tarlati are thanked for their contribution to the steady-state solvatochromic investigation.
KeyWords: INTRAMOLECULAR CHARGE-TRANSFER; NONLINEAR-OPTICAL PROPERTIES; N-METHYLPYRIDINIUM SALTS; EXCITED-STATE; PYRIDINIUM SALTS; 2ND HYPERPOLARIZABILITY; SOLVATOCHROMIC METHOD; DERIVATIVES; QUADRUPOLAR; INCLUSION
DOI: 10.1021/acs.jpcc.0c03536

Citations: 35
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