The absorption and emission properties of co-evaporated and bilayer phthalocyanine−perylene tetracarboxylic diimide (PTCD) thin films have been examined in search for new
emitters. The identification of exciplex emission in co-evaporated thin solid films of N,N'-bis(neopentyl)-3,4,9,10-perylenebis(dicarboximide) (BNPTCD) and titanyl(IV) phthalocyanine
(TiOPc) is reported for the first time. The efficiency of the exciplex emission is correlated
with a high degree of mixing in the co-evaporated mixed film. The homogeneity of the
emission from the surface of the mixed film is visualized using the global imaging technique.
The chemical detection of the mixing in the film is visualized using Raman global imaging.
The fact that exciplex formation is not a common occurrence when mixing these materials
is illustrated with the emission properties of co-evaporated mixed chloroindiumphthalocyanine (ClInPc)−BNPTCD films. In ClInPc−BNPTCD mixed films there is no exciplex emission
and in turn energy transfer is the main pathway for internal relaxation. For comparison,
bilayer films of BNPTCD/Pc were fabricated and studied as model systems of two separated
phases with a single interface. The effect of thermal annealing on film structure, molecular
organization, and phase separation in the mixed films was investigated using transmission
and reflection−absorption (RAIRS) infrared spectroscopy. The infrared data and AFM
topographical images provide information that allows one to correlate film structure with
the observed emission properties.
The cyclic voltammograms (CV) of N, N′-bis(propyl)-3,4,9,10-perylenebis(dicarboximide) [PTCDIPr] and N, N′-bis(neopentyl)-3,4,9,10-perylenebis(dicarboximide) [BNPTCD] in Langmuir-Blodgett (LB) films, in carbon paste electrode (CPE), and in solution for BNPTCD are reported here for the first time. The data allow a comparison of the electrochemical behavior of highly organized LB films with the results obtained on CPE, where the active molecules are randomly dispersed in a carbonaceous matrix. The electrochemical reduction waves indicate the reversible formation of stable radical anions and dianions. The discussion of reduction potentials is integrated with spectroscopic data and the HOMO-LUMO energy positions of both materials obtained from density functional theory computations.
Persistent photoconductivity (PPC) in vanadyl phthalocyanine (VOPc) organic light-emitting diodes was investigated using photoconductive time response, photocurrent–voltage characteristics and charge extraction in linearly increasing voltage (CELIV) measurements. The experiments were performed in phase 1 (amorphous) and in phase 2 (crystalline) samples obtained by the physical vapour deposition (PVD) technique over ITO/glass electrodes with an Al covering electrode. The results indicated a photoconductivity with a long decay time in phase 1 VOPc described by a stretched exponential relaxation. The device showed a rectifying behaviour and the mobility of holes was measured by CELIV, following a dispersive model. In crystalline samples the PPC effect was not observed and the dominant mechanism of transport of holes was hopping in a Gaussian density of states.
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