Reza-González Francisco A, Villatoro Emmanuel, Reza Mariana M, Jara-Cortés Jesús, García-Ortega Héctor, Blanco-Acuña Edgard F, López-Cortés José G, Esturau-Escofet Nuria, Aguirre-Soto Alan, Peon Jorge
Instituto de Química, Universidad Nacional Autónoma de México Ciudad de México Mexico
Unidad Académica de Ciencias Básicas e Ingenierías, Universidad Autónoma de Nayarit Tepic 63155 Mexico.
Chem Sci. 2023 Apr 24;14(21):5783-5794. doi: 10.1039/d3sc01223a. eCollection 2023 May 31.
Donor-acceptor Stenhouse adducts (DASAs) are important photo-responsive molecules that undergo electrocyclic reactions after light absorption. From these properties, DASAs have received extensive attention as photo-switches with negative photochromism. Meanwhile, several photochemical applications require isomerization events to take place in highly localized volumes at variable depths. Such focused photoreactions can be achieved if the electronic excitation is induced through a non-linear optical process. In this contribution we describe DASAs substituted with extended donor groups which provide them with significant two-photon absorption properties. We characterized the photo-induced transformation of these DASAs from the open polymethinic form to their cyclopentenic isomer with the use of 800 nm femtosecond pulses. These studies verified that the biphotonic excitation produces equivalent photoreactions as linear absorbance. We also determined these DASAs' two-photon absorption cross sections from measurements of their photoconverted yield after biphotonic excitation. As we show, specific donor sections provide these systems with important biphotonic cross-sections as high as 615 GM units. Such properties make these DASAs among the most non-linearly active photo-switchable molecules. Calculations at the TDDFT level with the optimally tuned range-separated functional OT-CAM-B3LYP, together with quadratic response methods indicate that the non-linear photochemical properties in these molecules involve higher lying electronic states above the first excited singlet. This result is consistent with the observed relation between their two-photon chemistry and the onset of their short wavelength absorption features around 400 nm. This is the first report of the non-linear photochemistry of DASAs. The two-photon isomerization properties of DASAs extend their applications to 3D-photocontrol, non-linear lithography, variable depth birefringence, and localized drug delivery schemes.
给体-受体斯滕豪斯加合物（DASAs）是重要的光响应分子，在吸收光后会发生电环化反应。基于这些特性，DASAs作为具有负光致变色特性的光开关受到了广泛关注。同时，一些光化学应用要求异构化事件在可变深度的高度局部化体积中发生。如果通过非线性光学过程诱导电子激发，就可以实现这种聚焦光反应。在本论文中，我们描述了用扩展给体基团取代的DASAs，这些基团赋予了它们显著的双光子吸收特性。我们使用800 nm飞秒脉冲表征了这些DASAs从开放的聚甲炔形式到其环戊烯异构体的光诱导转变。这些研究证实双光子激发产生的光反应与线性吸收等效。我们还通过测量双光子激发后的光转换产率来确定这些DASAs的双光子吸收截面。正如我们所展示的，特定的给体部分为这些体系提供了高达615 GM单位的重要双光子截面。这些特性使这些DASAs成为最具非线性活性的光开关分子之一。使用优化调谐的范围分离泛函OT-CAM-B3LYP在TDDFT水平上的计算，以及二次响应方法表明，这些分子中的非线性光化学性质涉及高于第一激发单重态的更高电子态。这一结果与它们的双光子化学与其在400 nm左右短波长吸收特征的起始之间的观察关系一致。这是关于DASAs非线性光化学的首次报道。DASAs的双光子异构化特性将其应用扩展到三维光控、非线性光刻、可变深度双折射和局部药物递送方案。
