Sub-Millisecond Thermally Isomerizing Azophenols for Optically Triggered Oscillating Materials

Sub-Millisecond Thermally Isomerizing Azophenols for Optically Triggered Oscillating Materials 

The most important parameter to consider in the overall performance of such materials is the maximum oscillation frequency of the photochromic oscillator, Vax which is defined according to Eq. (11.1). 

Importantly, not all azo dyes are useful for optical oscillation. In fact, for high values to be achieved, the light-sensitive azo compound should revert very quickly to its thermodynamically stable trans form in the dark, most desirably within the micro- or nanosecond temporal domain. Two different families of azo dyes have been described so far that could be suitable for this task 4-donor-4 -acceptor azobenzenes, also known as push-pull azo dyes, and azophenols. Indeed, both azo derivatives are well known to exhibit fast thermal isomerization rates under ambient conditions. Among all push-pull azo dyes, 4-A/ ,A/ -dimethylamino-4 -nitroazobenzene, has been considered, until a few years ago, as the fastest thermally isomerizing azo dye, with a relaxation time for its thermal back reaction ranging from 21 to 122 ms in alcoholic solutions. On the other hand, and as it has been described previously in this chapter, the 

12 in ethanol at 298 and 328 K. (Reproduced from Garcia-Amoros et al. [63]. Copyright (2014), with permission of Royal Society of Chemistry.) 

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