A Solvatochromic–Chemometric Framework to Resolve Subtle Polarity Microenvironment Differences in Cycloalkanes Driven by Molecular Conformation and Substituent Effects: A Proof-Of-Concept for Advanced Aviation Fuel Design

This proof-of-concept study explores the application of solvatochromism to resolve differences in the polarity microenvironment induced by nonpolar hydrocarbon compounds, specifically cycloalkanes. A solvatochromic probe based on Betaine 30 or Reichardt’s dye was designed, and UV–vis absorption spectra were recorded for a set of structurally diverse cycloalkanes. Multivariate analysis, incorporating Principal Component Analysis (PCA) and K-means clustering, was applied to the spectral data to introduce a novel polarity classification capable of capturing subtle differences in the polarity microenvironment of cycloalkanes, compounds traditionally regarded as uniformly nonpolar. This solvatochromic approach demonstrated high sensitivity in detecting and differentiating small polarity variations among closely related isomers, revealing that molecular conformation, stereochemistry, and the number, type, and position of alkyl substituents exert measurable effects on the polarity microenvironment of hydrocarbons. These findings are particularly relevant to the development of alternative synthetic aviation fuels, where small variations in cycloalkane composition can significantly influence fuel performance, including energy density, combustion efficiency, and material compatibility (e.g., O-ring swelling). Overall, this work underscores the utility of solvatochromic probes for differentiating among structurally similar organic compounds, revealing quantitative polarity microenvironment differences across cycloalkanes and provides a preliminary polarity microenvironment classification framework for evaluating subtle intermolecular interaction differences to complement traditional methods based solely on solvatochromic parameters such as E T (30) or normalized E N T values.