Patterned Redox Arrays of Polyarylamines II. Growth of Thin Films and Their Electrochemical Behavior

Thin films of tetra-p-anisyl-p-phenylenediamine, 1, and p-phenylenediamine (PD) with four pendent diarylamino (AA) groups (4AA/PD, 3) are prepared by vapor deposition under high vacuum. Film growth is studied by atomic force microscopy on mica surfaces. The thin films of 1 and 3 grow very differently. Arylamine 1 grows by a Volmer−Weber type mechanism while 3 grows by a Stranski−Krastanov-type mechanism. The films are amorphous as deposited but convert into crystalline phases upon thermal annealing. Cyclic voltammetry of the films on indium tin oxide coated glass electrodes indicates that the crystalline phase of 1 is oxidized at a higher potential than its amorphous phase. Controlled potential coulometry on 100 nm films shows that oxidation of the core PD group of the shell/core structure 3 is much slower than oxidation of the PD group of 1 in the film state, suggesting that oxidation of the higher E°‘ arylamino (AA) shell of 3 may be required for bulk charging of its film. The ability of the peripheral AA groups of 3 to electrochemically shield its core PD group is a unique electronic feature derived from the shell/core patterned architecture of this redox-gradient array.