Carroll Joshua A, Pashley-Johnson Fred, Klein Maciej, Stephan Theresa, Pandey Ajay K, Walter Michael, Unterreiner Andreas-Neil, Barner-Kowollik Christopher
School of Chemistry and Physics, Faculty of Science, Queensland University of Technology (QUT), 2 George Street, Brisbane 4000, Queensland, Australia.
Centre for Materials Science, Queensland University of Technology (QUT), 2 George Street, Brisbane 4000, Queensland, Australia.
J Am Chem Soc. 2025 Jul 30;147(30):26643-26651. doi: 10.1021/jacs.5c06961. Epub 2025 Jul 16.
Photochemistry is at the forefront of many modern technologies, from additive manufacturing to phototherapeutics to sun protection and organic synthesis. It is commonly believed that an absorbance spectrum, showing the likelihood of a photon to be absorbed by a chromophore at a given wavelength, is an accurate predictor of how well a photochemical process will proceed when irradiated with different colors of light. Over the past decade this paradigm has been repeatedly challenged for many photochemical systems, as a distinct mismatch between the absorption spectrum and the wavelength-resolved photochemical reactivity has been observed. Herein, we unravel the underlying mechanisms behind the mismatched reactivity and absorbance in photocycloadditions. Initially, we probe the impact that an equilibrium established between reversible photochemical processes has on the mismatch for a pyrene-chalcone molecule. Subsequently, we establish a critical link between photophysics and photochemistry with a theory based on the selective excitation of specific microenvironments, leading to molecular transitions that allow for favorable wavelength-dependent reactivity. Time-resolved and steady-state fluorescence spectroscopy measurements confirm the presence of this selectivity, with both displaying significant red-edge effects that are observed in the fluorescence spectroscopy literature, further supporting our theory. By synthetically tethering chromophores together, we evidence the importance of microenvironments and their wavelength-dependent excited-state lifetimes, presenting the missing link that explains the mismatch in many photochemical systems. The implications of the theory presented herein stretch from additive manufacturing to photodynamic therapy and beyond, meaning that researchers can leverage mismatched photochemical reactivity by simply changing the properties of the environment surrounding the chromophore.
光化学处于许多现代技术的前沿，从增材制造到光疗、防晒和有机合成。人们普遍认为，吸收光谱显示了在给定波长下光子被发色团吸收的可能性，是光化学过程在不同颜色光照射下进行得如何的准确预测指标。在过去十年中，对于许多光化学系统，这一范式不断受到挑战，因为已观察到吸收光谱与波长分辨的光化学反应性之间存在明显不匹配。在此，我们揭示了光环加成反应中反应性与吸光度不匹配背后的潜在机制。首先，我们探究了可逆光化学过程之间建立的平衡对芘 - 查耳酮分子不匹配的影响。随后，我们基于特定微环境的选择性激发建立了光物理与光化学之间的关键联系，从而导致分子跃迁，实现有利的波长依赖性反应性。时间分辨和稳态荧光光谱测量证实了这种选择性的存在，两者均显示出荧光光谱文献中观察到的显著红边效应，进一步支持了我们的理论。通过将发色团合成连接在一起，我们证明了微环境及其波长依赖性激发态寿命的重要性，揭示了解释许多光化学系统中不匹配现象的缺失环节。本文提出的理论的影响范围从增材制造到光动力疗法及其他领域，这意味着研究人员可以通过简单改变发色团周围环境的性质来利用不匹配的光化学反应性。
