Pawar Dnyaneshwari, Pandhare Reshma J, Kamble Rajesh M, Dutta Choudhury Sharmistha
Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
Department of Chemistry, University of Mumbai, Santacruz (E), Mumbai 400 098, India.
J Phys Chem B. 2025 Jul 10;129(27):6965-6974. doi: 10.1021/acs.jpcb.5c03087. Epub 2025 Jun 26.
Quinoxaline derivatives with donor-acceptor architectures exhibit interesting photophysics and are suitable for many optical applications. This study investigates the effect of solvent polarity and temperature on the fluorescence characteristics of three prototypical quinoxalines substituted with the aryl moieties, naphthalene, anthracene, or pyrene. Apart from excellent solvatochromism, which is a property common to many donor-acceptor-type fluorophores, these quinoxaline derivatives also show intriguing polarity-dependent thermochromism. It is revealed that this phenomenon arises because of polarity-dependent switching in the nature of the emissive state. In polar solvents, the quinoxalines with strong donor substituents can emit from both a less polar locally excited (LE) state and a highly polar intramolecular charge transfer (ICT) state, whose relative populations can be changed by temperature variation. Furthermore, it is found that variation in solvent polarity can change the nonradiative deactivation pathway of the excited state from a very effective decay due to intramolecular rotation that is coupled with the LE state, to intersystem crossing (ISC), which is accessible from the ICT state. Overall, this study provides an in-depth understanding of the excited-state dynamics of this class of molecules. The possibility of many excited-state processes, whose relative participations can be engineered by chemical substitution, temperature variation, or polarity changes, is expected to be useful for designing quinoxaline derivatives with desired fluorescence and stimuli-responsive properties.
具有供体-受体结构的喹喔啉衍生物展现出有趣的光物理性质，适用于多种光学应用。本研究考察了溶剂极性和温度对三种分别被萘基、蒽基或芘基取代的典型喹喔啉荧光特性的影响。除了具有许多供体-受体型荧光团共有的出色溶剂化显色特性外，这些喹喔啉衍生物还表现出引人注目的极性依赖性热致变色现象。研究表明，这种现象是由于发射态性质的极性依赖性转变所致。在极性溶剂中，带有强供体取代基的喹喔啉可从极性较小的局域激发（LE）态和极性较大的分子内电荷转移（ICT）态发射荧光，其相对比例可随温度变化而改变。此外，研究发现溶剂极性的变化可改变激发态的非辐射失活途径，从与LE态耦合的分子内旋转导致的非常有效的衰减，转变为可从ICT态发生的系间窜越（ISC）。总体而言，本研究深入了解了这类分子的激发态动力学。许多激发态过程的可能性，其相对参与程度可通过化学取代、温度变化或极性改变来调控，有望用于设计具有所需荧光和刺激响应特性的喹喔啉衍生物。
