Proton Conduction Crossover and Pyrophosphate Bond Formation of -PO3H- Substituted Naphtalenediimide Salts

The control of the molecular arrangement of functionalorganic & pi;-molecules using intermolecular electrostatic hydrogen-bondinginteractions has been attempted by using a supramolecular approach.The anionic N,N & PRIME;-bis(ethylphosphonate)-naphthalene diimide (DPNDI ( 2- )) is designed, in which proton conducting -PO3H- groups are introduced at the two N-sites of NDI core that exhibits excellent n-type semiconductor properties.The combination with Na+ and NH4 (+) formed single crystals of (Na+)(2)(DPNDI ( 2- ))& BULL;(H2O)(2.0) (1) and (NH4 (+))(2)(DPNDI ( 2- )) (2).Single crystals 1 and 2 formed a two-dimensional(2D) electronic structure with a herringbone-type NDI arrangement. Upon heating crystal 1, it transformedinto dehydrated crystal 1 & PRIME;, and further heatingto temperatures above 510 K caused the dehydration condensation reactionsbetween adjacent -PO3H- groupsin the crystal, forming pyrophosphate bonds (-PO2-O-PO2-) and crystal 1 & PRIME; was converted into the oligomer (oligo-1).In crystal 1 & PRIME;, the Na+ ion conductivitywas confirmed by AC impedance measurements. In crystal 2, proton conduction occurred within the 2D electrostatic NH4 (+)& BULL;& BULL;& BULL;PO3H- hydrogen-bondingnetwork. The proton conduction at low temperatures was dominated bythe Grotthuss mechanism and at higher temperatures by the Vehiclemechanism, with activation energies of 284 and 360 meV, respectively.The proton conductivity at T = 423 K for crystal 2 reached up to 1.5 x 10(-4) S cm(-1). The packing structure of thin films 1 and 2 was different from that of the bulk crystal,and their transient conductivities were smaller than those predictedfrom the 2D electronic structure. On the contrary, the mixed thinfilms of PMMA and 1 or 2 maintained a moleculararrangement similar to those of the bulk crystal and exhibited transientconductivities of 6.8 x 10(-4) and 6.9 x10(-4) cm(2) V-1 s(-1), respectively.