Two-Dimensional Infrared Spectroscopy and Principal Component Analysis Studies on a New Azobenzene Derivative Supramolecular System Based on Hydrogen Bonds

2003 ◽  
Vol 57 (8) ◽  
pp. 933-942 ◽  
Author(s):  
Yuqing Wu ◽  
Ya-Qiong Hao ◽  
Min Li ◽  
Chaowei Guo ◽  
Yukihiro Ozaki
Keyword(s):  
Principal Component Analysis ◽  
Hydrogen Bonds ◽  
Supramolecular Assembly ◽  
Principal Component ◽  
Correlation Spectroscopy ◽  
Supramolecular System ◽  
Two Dimensional ◽  
Temperature Dependent ◽  
2D Correlation Spectroscopy ◽  
2D Correlation Analysis

Infrared (IR) spectra of a supramolecular assembly with an azobenzene derivative and intermolecular hydrogen bonds have been measured in the temperature range from 30 to 200 °C to investigate heat-induced structural changes and thermal stability. Principal component analysis (PCA) and two kinds of two-dimensional (2D) correlation spectroscopy, variable–variable (VV) 2D and sample–sample (SS) 2D spectroscopy, have been employed to analyze the observed temperature-dependent spectral variations. The PCA and SS 2D correlation analyses have demonstrated that the complete decoupling of hydrogen bonds in the supramolecular assembly occurs between 110 and 115 °C, which is in good agreement with the results of a differential scanning calorimetry (DSC) study for the heating process. The PCA of the IR spectra in the region of 3600–3100 cm−1 has illustrated that there are at least four principal components for the different NH2 and CONH species in the present supramolecular system. The VV 2D correlation spectroscopy study has provided information about the structure and strength of hydrogen bonds of NH2 and CONH groups and their temperature-dependent variations. The different species of hydrogen-bonded NH2 and CONH groups in the supramolecular system can be clarified by the VV 2D correlation analysis. The VV 2D correlation analysis has also revealed the specific order of the temperature-induced changes in the hydrogen bonds of NH2 and CONH groups.

scholarly journals New Approach to Generalized Two-Dimensional Correlation Spectroscopy. 1: Combination of Principal Component Analysis and Two-Dimensional Correlation Spectroscopy

2002 ◽  
Vol 56 (12) ◽  
pp. 1562-1567 ◽  
Author(s):  
Young Mee Jung ◽  
Hyeon Suk Shin ◽  
Seung Bin Kim ◽  
Isao Noda
Keyword(s):  
Principal Component Analysis ◽  
Correlation Analysis ◽  
Principal Component ◽  
Component Analysis ◽  
Correlation Spectroscopy ◽  
Data Matrix ◽  
Two Dimensional ◽  
Noise Component ◽  
Reconstructed Data ◽  
2D Correlation Analysis

The direct combination of chemometrics and two-dimensional (2D) correlation spectroscopy is considered. The use of a reconstructed data matrix based on the significant scores and loading vectors obtained from the principal component analysis (PCA) of raw spectral data is proposed as a method to improve the data quality for 2D correlation analysis. The synthetic noisy spectra were analyzed to explore the novel possibility of the use of PCA-reconstructed spectra, which are highly noise suppressed. 2D correlation analysis of this reconstructed data matrix, instead of the raw data matrix, can significantly reduce the contribution of the noise component to the resulting 2D correlation spectra.

Mechanism of Thermal Phase Transition of a Ferroelectric Liquid Crystal with Monotropic Transition Temperature Studied by Infrared Spectroscopy Combined with Principal Component Analysis and Sample—Sample Two-Dimensional Correlation Spectroscopy

2005 ◽  
Vol 59 (5) ◽  
pp. 620-629 ◽  
Author(s):  
Jinggang Zhao ◽  
Kenji Tatani ◽  
Yukihiro Ozaki
Keyword(s):  
Phase Transition ◽  
Principal Component ◽  
Correlation Spectroscopy ◽  
Heating Process ◽  
Ferroelectric Liquid Crystal ◽  
Two Dimensional ◽  
Thermal Dynamics ◽  
Alkyl Chains ◽  
The Core ◽  
2D Correlation Spectroscopy

Infrared (IR) spectra of FLC-154 (FLC: ferroelectric liquid crystal) with monotropic phase transition under a nonalignment state with a sample layer thickness of 24.5 μm were measured for heating process from 55 to 90 °C and a cooling process from 90 to 55 °C in increments of 1 °C. The thermal dynamics of FLC-154 were investigated by use of IR spectroscopy combined with principal component analysis (PCA) and sample–sample two-dimensional (2D) correlation spectroscopy. During the cooling, the FLC-154 molecule passes through the monotropic smectic- C* (Sm- C*) phase, which is transformed from the Sm- A phase. The results from PCA suggest that during the heating process, the thermal dynamics of the alkyl chains, core moiety, and C=O groups are similar to each other. Furthermore, PCA and sample–sample 2D correlation spectroscopy indicate that the alkyl chains and C=O groups in the chiral and core moieties are responsible for the emergence of the Sm- C* phase. This conclusion is very important because the IR data have given more evident cause for the emergence of the Sm- C* phase than the theoretical models such as the molecular-statistical theory of ferroelectric ordering and the indigenous polarization theory. Moreover, it has been found that some of the trans conformations of the alkyl chains of FLC-154 change partly to the gauche conformation when the phase transition from the crystalline phase to the Sm- A phase occurs. It has also been found that the intermolecular interactions of the C=O group in the core moiety in the Sm- A phase are weaker than those in the crystalline phase and that the conformational change occurs on the C–O–C bonds in the core moiety upon going from the crystalline to the Sm- A phase.

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