Spectroscopic quantification of aggregation-dependent spectral changes in phthalocyanines: a metric framework and...

Concentration-dependent spectral changes in functional dyes are critical for optoelectronic applications yet remain poorly quantified. Here, we introduce a physically meaningful metric system based on UV-Vis spectroscopic data that translates spectral behavior into compact descriptors by decoupling underlying amplification and attenuation processes. Systematic extinction studies on six novel 2,3-dibenzyloxy-tert-butyl-substituted phthalocyanines (3a-f) with varied central ions (metal-free, Mg, Zn, Cu, Ni, Co) reveal three distinct types of concentration behavior predicted by the electronic structure of the central ions: (i) classical H-aggregation with intensity transfer for Ni (ENI = 55,316, DPI = +0.971 at Q-band and - 0.990 at H-band, NC = 4.14); (ii) a sharp, cooperative hyperchromic effect for Co (RWI = 0.50, NC = 5.10); and (iii) weak, non-specific attenuation for Mg, Zn, Cu, and the ligand (NC = 0.73-3.43). Our metrics quantitatively resolve these behaviors, with the composite Normalized Cooperativity index (NC) successfully ranking the compounds; thus, Ni (NC = 4.14) and Co (NC = 5.10) show an order of magnitude higher cooperativity than the other dyes (NC = 0.73-1.31). Crucially, the CORRELATO algorithm was employed as an unbiased validator, autonomously identifying stable high-correlation relationships (r_xy > 0.95) and selecting the composite NC index as the key classifying parameter. This provides rigorous proof that our metrics are objective physical measures, not arbitrary constructs. By offering a validated, quantitative framework covering both synthesis prediction and property analysis, this work transforms aggregation analysis from a descriptive art into a predictive science.