“…Although thermochromism is also observed for a solid thin film of PDHS, its T c is relatively higher (315 K), and one of the phases has a different absorption peak at 374 nm . Our present result is very interesting in that EG-PDHS chains behave like PDHS in dilute solution even in solventless conditions: T c is comparable to that in dilute solution, and more obviously, the longer wavelength absorption band appears at the same wavelength as that of PDHS in dilute solution (353 nm) but for PDHS solid thin film (374 nm) …”
“…Although thermochromism is also observed for a solid thin film of PDHS, its T c is relatively higher (315 K), and one of the phases has a different absorption peak at 374 nm . Our present result is very interesting in that EG-PDHS chains behave like PDHS in dilute solution even in solventless conditions: T c is comparable to that in dilute solution, and more obviously, the longer wavelength absorption band appears at the same wavelength as that of PDHS in dilute solution (353 nm) but for PDHS solid thin film (374 nm) …”
“…In Figure , the λ max values obtained from Figure are plotted against 〈|φ|〉. On the vertical line of 〈|φ|〉 = 0, however, the λ max value of 374 nm is plotted instead of λ max = 363 nm. , The data, collected from three PSs, appear to form a master curve. 11 Correlation between UV absorption maximum (λ max ) and average dihedral angle (〈|φ|〉): (○) PDBS, (▵) PDHS, and (□) PMPrS.…”
Conformational characteristics of poly(di-n-butylsilane) (PDBS), poly(di-n-hexylsilane) (PDHS), and poly(methyl-n-propylsilane) (PMPrS) have been investigated by a rotational isomeric state (RIS) scheme with
molecular dynamics simulations. Characteristic ratios thus calculated for PDBS, PDHS, and atactic PMPrS
are, respectively, 42.0, 54.0, and 12.3, being comparable to our light-scattering measurements. In the ϑ state,
most Si−Si bonds of PDBS and PDHS adopt deviant ± (D±) conformations (dihedral angles ≈ ±150°); in
adjacent Si−Si bonds, D±D± conformations are the most stable, and D±D∓ states have a slightly higher
energy of ca. 0.1 kcal mol-1. This is the reason for their rigidity in solution and the formation of a disordered
structure. An RIS treatment for pseudoasymmetric polymers with different side chains (R and R‘) (e.g.,
[-SiRR‘-]
x
and [-CRR‘-]
x
) has been developed. By this method, the characteristic ratio of atactic PMPrS was
obtained as above, and the stereosequence dependence of the spatial configuration of PMPrS was investigated;
the characteristic ratio increases with the meso-diad probability. The UV absorption maxima (λmax) of PDBS,
PDHS, and PMPrS were correlated with average dihedral angles evaluated from the RIS calculations. The
solubility of polysilanes has also been elucidated in terms of conformation.
“…Among the silanes, poly(di-n-hexylsilane) (PDHS) has been investigated by many researchers because it shows a phase transition with thermochromism above room temperature. 3,4) We have successfully described the crystal structure of PDHS, in which the silicon backbone has an all-trans conformation, whereas the n-hexyl substituents have an asymmetical conformation. 5,6) The primitive unit cell contains two polymer chains, which are not equivalent, and these chains are closely packed in space because of the van der Waals forces.…”
To investigate the photodecomposition mechanism of poly(di-n-hexylsilane) (PDHS), the ultraviolet (UV) light irradiation time dependence of the optical absorption (OA) and the piezoelectric photothermal (PPT) signals were measured in vacuum. A strong OA peak at 370 nm and a broad OA band at approximately 320 nm related to the all-trans and helical conformations, respectively, were observed. With increasing UV light irradiation time, their intensities decreased and blue shifts were observed because of the decomposition of Si-Si bonds in the silicon backbone. In the PPT spectrum, a nonradiative recombination peak associated with the all-trans conformation was also observed at 370 nm. When UV light irradiated the sample, in addition to the decrease in the intensity and the blue shift of the PPT peak at 370 nm, new PPT signals at approximately 290 nm were observed. We concluded that these signals were caused by the silicon and/or carbon dangling bonds generated by photodecomposition in vacuum. #
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