Effect of Spectral Shifts on the Resolution of trans-1-(2-Naphthyl)-2-phenylethene Conformer UV Spectra Based on Principal Component Analysis with Self-Modeling

Application of principal component analysis with self-modeling (PCA-SM) to a matrix consisting of UV absorption spectra of trans-1-(2-naphthyl)-2-phenylethene (NPE) at different temperatures leads to two resolved pure component spectra. The significance of this resolution is evaluated by examining the spectra of three conformationally restricted NPE analogues: trans-1-[2-(1-methylnaphthyl)]-2-phenylethene (1-MPE), trans-1-[2-(3-methylnaphthyl)]-2-phenylethene (3-MPE), and trans-3-styrylidenebenz[e]indane (BPE). It is established that temperature effects on the UV spectra of NPE reflect primarily the temperature dependence of the individual conformer spectra rather than any changes in conformer composition. Pure component UV absorption spectra generated by PCA-SM on the spectrothermal matrix of NPE UV spectra bear no resemblance to either the analogue spectra or the known NPE conformer spectra. PCA-SM treatment of a simulated spectral matrix shows that spectral shifts are reflected predictably in the appearance of the second eigenvector. The implications of our findings on results obtained from other PCA-SM spectral resolutions of spectrothermal matrices are discussed.