This study focuses on a liquid type light-emitting device with simple structure, an organic electrochemiluminescence (ECL) device. To realize long luminescence, polymer ECL devices using pconjugated polymers, poly(2,5-dioctylphenylene-1,4-ethynylene) (PPE) and poly(3-octylthiophene-2,5diyl) (P3OT), were fabricated. The luminescence properties of each device were investigated. Both polymer ECL devices exhibit luminescence from an excited-state polymer which is formed by redox and annihilation reaction. In particular, a low threshold voltage of about 2.4 V and long luminescence for about 6000 s were obtained from the P3OT ECL device. This is a longer luminescence than from a typical low molecular ECL device using a ruthenium complex. Moreover, the concentration of emitting material and the frequency applied were important parameters in order to obtain the long luminescence. Applying high frequency AC voltage (5.0 V at 1000 Hz) to the emitting solution with moderate P3OT concentration of 3.0 wt% emitted light for a long period. On the other hand, the PPE ECL device suggested the instability of the radical cation and its luminescence conditions were stringent.Its luminescence was short (about 180 s).

In this study, we report the light-emitting assistance effect of perylene on a polymer electrochemiluminescence (ECL) device using poly(3-octylthiophene-2,5-diyl) (P3OT). An ECL device is a liquid type self-luminous device with a simple structure, and can be fabricated by a relatively easy procedure. Significant improvement in luminescence properties was confirmed when 1.0 wt % perylene was added to the ECL device using 3.0 wt % P3OT. Improvements of about 12 times of the maximum luminescence intensity and about 23 times of the light-emitting time ratio compared with that of a P3OT ECL device were obtained. We conclude that the light-emitting assistance of perylene is achieved by perylene radical ions shuttling electrons to P3OT while they are moving around in the emitting solution. The light-emitting assistance effect of perylene was also confirmed when poly(3-dodecylthiophene-2,5-diyl), which has almost identical electrochemical and photophysical characteristics to those of P3OT, was used instead of P3OT.

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