The Dark Side of Crystal Engineering:Creating Glasses from Small Symmetric Molecules that Form Multiple Hydrogen Bonds

摘要

Amorphous molecular materials (molecular glasses) are a prime source of isotropic thin films for use in optoelectronic devices.At present,molecular glasses are most commonly derived from polymers,but compounds of low molecular weight can also exist in amorphous forms with high glass transition temperatures (T_g > 25 deg C).Because such glasses are derived from small molecules,they offer the advantage of working with materials of precise mass,well-defined composition,high purity,and good processability.However,materials made from small molecules tend to reach thermodynamic equilibrium quickly,thereby converting amorphous forms into ordered crystalline phases.Few low-molecular-weight glasses can forestall this process indefinitely,especially at temperatures above T_g.