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The terahertz spectrum of paper has been measured from room temperature to cryogenic temperatures. As the paper is cooled, the main absorption lines move to higher frequencies. The same behaviour is observed for two types of paper. The spectrum at base temperature provides the most direct comparison yet with calculations made using density functional theory, which assume the studied material to be at absolute zero temperature. These unique experiments should spur the development of better theoretical models of cellulose and cognate materials. [ABSTRACT FROM AUTHOR]

For many centuries, paper was considered the main support for recording cultural achievements all over the world. Archives represent the historical memory of our past, and the book conservation represents one main concern since many books and documents kept in libraries and archives are at risk because of their fragility. The use of portable, not destructive technique like NIR μ-Raman spectroscopy represents a valid instrument for monitoring the documentary heritage. In the present study, we investigated the degradation process, associated to the polymers breaking, in order to propose a successful kinetic model for determining the ageing time of cellulose. We compared the calculated results with respect to both experimental samples and literature data, covering a period of seven centuries, from XV to XXI centuries. Proposed model starts directly from Raman spectra, in particular by monitoring the band at 1100 cm − 1 ascribed to C-O-C inter-monomers bond, whose relative intensity is related to the cellulose chain length. We obtained a very good agreement with the experimental data with 8% of accuracy. Finally, with the help of Density Functional Theory (DFT) simulations, we confirmed our model by studying the structure and the grade of cellulose crystallinity in the paper. In particular, the reverse trend of the band at 900 cm − 1 , related to the crystallinity grade of the cellulose, and the band at 1100 cm − 1 , as a function of the dimer unit cell structure, supported the kinetic model, suggesting a shear stress like effect as the origin of the cellulose chain length decrease. [ABSTRACT FROM AUTHOR]

In this study, we reported the photoluminescence (PL) behaviour of a new intramolecular charge transfer (ICT) compound, ((E)-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)benzoic acid, (HABA), which shows ICT solvent effect in aprotic solvents as confirmed by absorption and emission spectra. While in protic solvents including water and ethanol, the charge transfer (CT) band significantly reduces. Remarkable fluorescence enhancement in the blue region was also observed for HABA in polar protic solvents. We described such phenomena as “specific solvent effect”. It can be ascribed to the hydrogen bonding formation between HABA and protic solvents, which not only causes significant reduction in the rate of internal conversion but also elevates the energy gap. Density functional theory (DFT) calculations as well as the dynamics analysis were performed to further verify the existence of hydrogen bonding complexes. Stronger emission turn-on effect was observed on HABA solid film when it is treated with water and base solution. The stimuli-responsive fluorescence of HABA enables a new green printing technique that uses water/base as the ink, affording fluorescent handwritings highly distinct from the background. Thermoanalysis of the dye suggests the nice thermostability, which is highly desired for real-world printing in a wide temperature range. [ABSTRACT FROM AUTHOR]

Paper is an important material for many applications. During the centuries, it has been the most widely used writing support and therefore paper degradation is a major issue for cultural heritage. The main component of paper is cellulose, one of the most abundant biomaterials on Earth. Cellulose oxidation is mainly responsible for the yellowing of the ancient samples, through the formation of chromophores. In order to investigate this issue and the chromophores' role, we exploit the optical properties combining non-destructive experiments and theoretical calculations based on ab-initio techniques. In this paper, we illustrate the method and show its application to three ancient paper samples. The procedure we describe is a precious tool for cultural heritage preservation: indeed, the approach we present is based on non-invasive and non-destructive measurements that allows a microscopic understanding of cellulose-based artifacts degradation. [ABSTRACT FROM AUTHOR]

To advance our understanding of the molecular biochemistry of fungi which impact cultural heritage in libraries, museums and archives we investigated the diagnostic capacity of Raman spectroscopy to identify the composition of colored chromophores of fungi on paper. In this study we explored the diagnostic capacity of resonant Raman to distinguish chromophores in fungal filaments stimulated to grow on paper under high humidity with a focus on characterizing chromophores of Alternaria group species. To facilitate molecular analysis, we conducted quantum chemistry calculations of representative metabolites having optical absorption in the ultraviolet–visible spectral range. Comparing theory and experiment we show that fonsecin, erythroglaucin and aurasperone type chromophores occur in mature hyphal filaments with β-carotene dominant in yeast depositions on paper surfaces. Resonant Raman of mature filaments suggests a further contribution of carotenes longer than β-carotene to the spectral signature. Using microscopic resolution, we distinguish rich sets of Raman signatures that we assign to lignin, flavoglaucin, riboflavin, cycloleucomelon(e) and asperyellone molecular components in the spatial regions where filaments initiate from yeast depositions. In such regions, where filament microstructures stimulate development of a mature three-dimensional scaffold, the diversity of Raman resonances confirms a rich biochemistry of the developing structures. The library of computed optical and spectroscopic responses of characteristic fungal chromophores and metabolites presented here is essential for understanding the effect of fungi on a wide range of objects made from paper including books, prints, drawings, watercolors, engravings and even sculptures as well as designing next generation materials based on fungal hyphal mats. • Non-invasive Raman spectroscopy can be used to identify pigments in fungi. • Quantum chemistry (DFT) combined with Raman for quantitative measure of chromophores. • Computed optical responses of fungal chromophores and metabolites. • Raman spectroscopy combined with Quantum chemistry as tools for cultural heritage. • Alternaria sp. generates specific pigments when grown on paper. [ABSTRACT FROM AUTHOR]