Modulation in Molecular Materials - Variable Temperature

Modulation occurs when there is ordering on two (or more) length scales. When the ratio of these is an integer, the modulation is said to be commensurate, i.e. one ordering is commensurate with the other. When the ratio is an irrational number it is said to be incommensurate and the periodicity of the two coincide rarely if ever. Modulation in solid-state materials is a well known phenomenon and the impact it can have on physical properties is understood within the research community. However, in molecular materials it has been reported rarely and is often seenas a curiosity, or worse, an inconvenience. With the advent of high intensity sources and increasingly sensitive detectors, it is becoming more difficult toignore these aperiodic features. We have been studying a series of compounds that show modulation in order to better understand its behaviour in the molecular solid state.