Substituent effects on the UV absorption energy of 2,5‐disubstituted pyrimidines

Abstract

Pyrimidine-containing molecules have been extensively investigated in organic light emitting devices (OLEDs), solar cells, liquid crystals, and so on due to their perfect photoelectric properties. Ultraviolet (UV) absorption is one of the interesting photoelectric properties. Systematical study of the substituent effects on the UV absorption energy of pyrimidine derivatives will guide to design functional molecules with specific photoelectric properties. In this paper, thirty-seven 2-X-5-Y pyrimidines with various substituents (X/Y=NH 2 , CH 3 , OCH 3 , NMe 2 , CF 3 , NO 2 , Cl, Br, I) were synthesized, and their UV spectra were recorded in anhydrous ethanol. The maximum absorption wavelength λ max (nm) were obtained and converted to wavenumber ν max (cm -1 ) (ν max = 1/λ max ) for quantitative structure-property relationship study. Hammett parameters (σ, σ F , σ R ), electronegativity (χ), the excited-state substituent effect parameter (σ ex CC ), and the heavy atom effect indicator (D) were employed as descriptors characterizing the molecular structure. By stepwise regression, a 5-descriptor linear regression model was built as ν max = 35 864.8122 + 6743.7901σ R (X) + 8587.9937σ R (Y) − 2042.7280Δσ 2 + 1106.0034D(X) + 1451.8873χ(X) (R = 0.9861, S = 693.70, ARD = 1.49%, F = 218.68, R cv = 0.9775, S cv = 881.25, ARD cv = 1.82%, n = 37). The model is proved of good stability and predictive performance by leave-one-out cross validation. Compared with the benzylideneaniline derivatives with C═N bridge group, the substituent effects on the UV absorption energy of 2,5-disubstituted pyrimidines are quite different and much more complex. KEYWORDS 2,5-disubstituted pyrimidine, quantitative structure-property relationship, substituent effect, UV absorption

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