Investigation of the thermal stability of electrooptical dyes
The thermal analysis of several hundred electro-optical (EO) dyes is presented. The thermal stability of the dyes is measured by their decomposition temperatures using Differential Scanning Calorimeter (DSC). It is found that the thermal stability of the dyes depends on two factors: molecular structure and concentration. For neat samples, the stability of dyes having different electron acceptor groups increases in the order of the following: nitro(NO2), tricyanovinyl, dicyanovinyl, cyano(-CN). The statistical analysis concludes that atoms with attached hydrogen atoms are sites of increased instability. It is also suggested that the intramolecular or intermolecular interaction between the electron donors and electron acceptors contributes to the thermal instability of the dyes. This situation can be modified with the separation of the dye molecules by mixing them with inert solvent molecules such as biphenyl and naphthalene. The thermal stability of the dyes in the diluted solid solution increases with the decrease of their concentration. The enhancement can be as high as 100$C. This enhancement depends on the nature of the dyes. The significance of the dilution studies lies in the fact that the EO dyes implemented in the real optical devices are surrounded by polymeric materials and so that they will display a much higher thermal stability than might have been expected. It also suggests that introducing large non-reactive fragments such as phenyl rings around the donor or acceptor of dye's molecular structures will diminish the molecular interaction between the donor and acceptors. ^ Several correlation models have been established for the set of dye molecules. Although the simplest structural descriptors do indicate some relationship to the thermal stability, it is found that the descriptors which possess more detailed structural information will have a better correlation. Hence, a set of molecular descriptors based on the nearest neighboring connectivity and the hybridization of the atoms, together with the interaction terms, produces a high correlation coefficient. The model appears to be stable with regards to prediction. The similarity index is also used to build several models and give very high correlation coefficients. ^
Engineering, Materials Science
Zhang, Lixia, "Investigation of the thermal stability of electrooptical dyes" (1999). ETD Collection for University of Texas, El Paso. AAI9937184.