Indolic Squaraines as Two-Photon Absorbing Dyes in the Visible Region: X-ray Structure, Electrochemical, and Nonlinear Optical Characterization

Abstract

We present the design, synthesis, and structural characterization of short conjugation length squaraine structures having relevant two-photon absorption (TPA) performances in the 700−800 nm regime. We show in particular how it is possible to tune the TPA performances, only marginally affecting the linear absorption.

Squaraine Compounds: Tailored Design and Synthesis towards a Variety of Material Science Applications

“…Finally Beverina and Pagani prepared the first indolizine-derived squaraine 11 in the context of reactive oxygen species sensitization [24] and squaraine 12 in the context of optical limiting. [25] Note that the regiochemistry of indole reaction with squaric acid follows the standard rule for electrophilic substitution on this substrate. No 2-substituted squaraine was isolated and the regiochemistry of the reaction was confirmed by single-crystal X-ray (Scheme 4, d).…”

“…No 2-substituted squaraine was isolated and the regiochemistry of the reaction was confirmed by single-crystal X-ray (Scheme 4, d). [25] …”

Zweiphotonenabsorption und das Design von Zweiphotonenfarbstoffen

“…[51] Squarainfarbstoffe sind eine weitere Chromophorklasse mit elektronenarmer zentraler Einheit. Die Verbindungen 16 [52] und 17 [41] zeigten eine beachtliche 2PA. Einen Extremfall von Elektronenakzeptoren stellen Carbokationen dar; entsprechend zeichneten sich durch carbokationische Einheiten verbrückte Porphyrindimere durch eine sehr starke 2PA aus.…”

Pyrrolyl Squaraines–Fifty Golden Years

“…Reports of large third-order susceptibilities, based on the observance of large two-photon absorption cross-sections, have continued [29]. Other studies have been undertaken that just concentrate on the large two-photon absorption cross-sections that pyrrolyl squaraine dyes exhibit [32,33,52,55,66]. Following the discovery that symmetrical bis(anilino)squaraine dyes exhibit second-order nonlinear optical effects as Langmuir-Blodget deposited monolayers on hydrophilic glass slides [93], results for a range of pyrrolyl squaraines were similarly reported [11,13,14].…”

“…Electrical conductivity measurements have exclusively been undertaken on pyrrole-derived polysquaraines. However, pyrrolyl squaraine dyes have undergone cyclic voltammograms to measure their redox chemistry [23,33,39,49,51,53,57,63,68] as have pyrrole-derived poysquaraines [30,41,49,50,54]. It is also worth noting that current density verses voltage (or J-V) curves have been measured, particularly on organic photovoltaics containing pyrrolyl squaraines [35,45,48,51,67].…”