Thermochromism, dialkyl-poly

In solution, poly(dialkyl)germanes such as (n-IIexjGe),. (H-Pen2Gc)n and (n-Bu2Ge) show a distinct thermochromic behaviour31,55. The kmax value of (n-Hex2Ge) in pentane gradually shifts from kmax = 340 nm at room temperature to kmax = 350 nm at — 60 °C. 

Order-Disorder Transitions. General Features, Experimental data are summarized in Table II, and representative thermochromic behaviors are shown in Figure 2. For the dialkyl-substituted polysilylenes the transition is very sharp, with a barely discernible coexistence region and an approximate isosbestic point. On the other hand, the asymmetrically substituted polymers, except poly(n-dodecylmethylsilylene), display very smooth behavior only in n-hexane solution and a broad but clearly discernible transition in dilute toluene solution. The transition width (ATc) in toluene solution was taken to be the interval between departure from the extrapolated, smooth, high-temperature behavior and the onset of peak absorption wavelength saturation at low temperature. The transition temperature (Tq) is defined arbitrarily as the midpoint of this region. 

The poly(dialkyl) stannanes, (Hex2Sn) and (Oct2Sn) exhibit a reversible thermochromic behavior upon warming above room temperature. The A. iax values of these polymers undergo a blue-shift from 384 to 369 nm for poly(di-n-octyl)stannane between 30 0 °C in toluene and from 392 to 382 nm in... 

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