Savaş İpek, Çelik Mehmet Efe, Barsella Alberto, Dengiz Cagatay
Department of Chemistry, Middle East Technical University, 06800, Ankara, Turkey.
Département d'Optique Ultra-Rapide et Nanophotonique, IPCMS-CNRS, 23 Rue du Loess, BP 43, 67034, Strasbourg, Cedex 2, France.
Chemistry. 2025 Mar 3;31(13):e202404778. doi: 10.1002/chem.202404778. Epub 2025 Jan 31.
This study introduces a new donor group capable of activating click-type [2+2] cycloaddition-retroelectrocyclizations, generally known for their limited scope. Target chromophores were synthesized using isocyanate-free urethane synthesis. The developed synthetic method allows for the tuning of the optical properties of the chromophores by modifying the donor groups, the acceptor units, and the side chains. The charge transfer (CT) bands of the chromophores exhibit λ values ranging from 363 to 692 nm. The CT bands observed have been supported by solvatochromism and protonation experiments. The synthesized compounds exhibit positive solvatochromism. Due to their potential as NLOphore candidates, the stability of the synthesized compounds have been investigated both experimentally through TGA and theoretically by calculating parameters such as frontier orbital energy differences, electronegativity, and global hardness/softness. TD-DFT calculations were used to elucidate the nature of the electronic transitions, revealing that the bands correspond to CT arising from HOMO-to-LUMO excitations. The NLO properties of the chromophores were investigated theoretically by DFT methods and experimentally by the EFISHG technique. Both results are shown to be in agreement with HOMO-LUMO energy differences. The experimental μβ values of the selected molecules range from 470×10 to 5400×10 esu.
本研究引入了一个能够激活点击型[2+2]环加成-逆电环化反应的新供体基团，这类反应通常范围有限。目标发色团通过无异氰酸酯的聚氨酯合成法制备。所开发的合成方法能够通过修饰供体基团、受体单元和侧链来调节发色团的光学性质。发色团的电荷转移（CT）带的λ值范围为363至692 nm。观察到的CT带已得到溶剂化显色和质子化实验的支持。合成的化合物表现出正溶剂化显色性。由于它们作为非线性光学发色团候选物的潜力，已通过热重分析（TGA）实验研究了合成化合物的稳定性，并通过计算前沿轨道能量差、电负性和全局硬度/软度等参数进行了理论研究。采用含时密度泛函理论（TD-DFT）计算来阐明电子跃迁的性质，结果表明这些带对应于由最高占据分子轨道（HOMO）到最低未占据分子轨道（LUMO）激发产生的电荷转移。通过密度泛函理论（DFT）方法对发色团的非线性光学性质进行了理论研究，并通过电场诱导二次谐波产生（EFISHG）技术进行了实验研究。结果表明，这两种结果均与HOMO-LUMO能量差一致。所选分子的实验μβ值范围为470×10至5400×10 esu。
