A time-temperature integrator based on fluorescent and polymorphic compounds

Denis Gentili, Margherita Durso, Cristian Bettini, Ilse Manet, Massimo Gazzano, Raffaella Capelli, Michele Muccini, Manuela Melucci & Massimiliano Cavallini

Scientific Reports 2013, 3, Article number: 2581.


Despite the variety of functional properties of molecular materials, which make them of interest for a number of technologies, their tendency to form inhomogeneous aggregates in thin films and to self-organize in polymorphs are considered drawbacks for practical applications. Here, we report on the use of polymorphic molecular fluorescent thin films as time temperature integrators, a class of devices that monitor the thermal history of a product. The device is fabricated by patterning the fluorescent model compound thieno(bis)imide-oligothiophene. The fluorescence colour of the pattern changes as a consequence of an irreversible phase variation driven by temperature, and reveals the temperature at which the pattern was exposed. The experimental results are quantitatively analysed in the range 20–200°C and interpreted considering a polymorph recrystallization in the thin film. Noteworthy, the reported method is of general validity and can be extended to every compound featuring irreversible temperature-dependent change of fluorescence.