Paul Debasish, Sahoo Priyadarshi, Sengupta Arunava, Tripathy Umakanta, Chatterjee Soumit
Department of Chemistry and Chemical Biology, Indian Institute of Technology (Indian School of Mines) Dhanbad, Dhanbad826004, Jharkhand, India.
Department of Physics, Indian Institute of Technology (Indian School of Mines) Dhanbad, Dhanbad 826004, Jharkhand, India.
J Phys Chem B. 2025 Jan 16;129(2):692-711. doi: 10.1021/acs.jpcb.4c04104. Epub 2024 Oct 31.
Three novel core green fluorescent protein (GFP) chromophore analogues, based on a doubly locked conformation and variable electronic effects by replacing one hydrogen with bromine, iodine, and methyl, respectively, have been synthesized to modulate the push-pull effect. These chromophores exhibited intramolecular H-bonding, as evidenced by single-crystal X-ray and H NMR studies. The fluorescence quantum yields (ϕ) of all of the chromophores were found to be more than an order of magnitude higher (∼0.2) than the unlocked chromophores (∼0.01). It was found that the electronic effect did affect the nonradiative rates, as the quantum yields were found to vary with respect to different analogues in the same solvents. The effect of the push-pull effect was also evident by a higher Stokes-shifted emission in the case of the methyl derivative with respect to the bromo- and iodo-analogues. Furthermore, the emission spectra of these GFP chromophores were found to show positive solvatochromism, which was supported by a quantum chemical calculation. A detailed study, correlating the observed spectral changes with various solvent functions and supported by computational results, established a facile proton transfer, followed by twisted intramolecular charge transfer (TICT) to be the major nonradiative channels of these chromophores. Besides, a completely novel usage of these chromophores was explored for the first time by studying their third-order nonlinear optical characteristics in DMSO using a single-beam Z-scan technique. All of the chromophores exhibited tunable nonlinear refraction (NLR) and nonlinear absorption (NLA) properties that depend upon different substituent groups present in the chromophores. Here, the NLR was due to the effect of self-defocusing, whereas the NLA was triggered by reverse saturable absorption, which is attributed to the two-photon absorption (TPA) process. Surprisingly, the efficiency of the TPA ability of the chromophores was found to be a function of the induced electronic effect. Hence, this work opens a new route for the utility of the -locked GFP chromophores in the field of nonlinear optical applications.
基于双锁定构象以及分别用溴、碘和甲基取代一个氢所产生的可变电子效应，合成了三种新型核心绿色荧光蛋白（GFP）发色团类似物，以调节推挽效应。单晶X射线和氢核磁共振研究表明，这些发色团呈现分子内氢键。发现所有发色团的荧光量子产率（ϕ）比未锁定的发色团（约0.01）高出一个数量级以上（约0.2）。结果发现，电子效应确实影响非辐射速率，因为在相同溶剂中，量子产率随不同类似物而变化。甲基衍生物相对于溴代和碘代类似物具有更高的斯托克斯位移发射，这也证明了推挽效应的影响。此外，发现这些GFP发色团的发射光谱呈现正溶剂化显色，这得到了量子化学计算的支持。一项详细研究将观察到的光谱变化与各种溶剂函数相关联，并得到计算结果的支持，确定了一个容易发生的质子转移，随后是扭曲分子内电荷转移（TICT），这是这些发色团的主要非辐射通道。此外，通过使用单光束Z扫描技术研究它们在二甲基亚砜中的三阶非线性光学特性，首次探索了这些发色团的全新用途。所有发色团都表现出可调谐的非线性折射（NLR）和非线性吸收（NLA）特性，这取决于发色团中存在的不同取代基。在这里，NLR是由于自散焦效应，而NLA是由反向饱和吸收引发的，这归因于双光子吸收（TPA）过程。令人惊讶的是，发现发色团的TPA能力效率是诱导电子效应的函数。因此，这项工作为锁定GFP发色团在非线性光学应用领域的实用化开辟了一条新途径。
