Recently

9 new soluble organic small molecular electroluminescent materials

derivatives of Alq

3

have been synthesized in our laboratory and Almq

2

-OH of these materials has very good blue electroluminescent characteristics.To investigation further electroluminescent properties of these materials we focus on the measurements of energy level structure parameters of the 9 soluble organic small molecules using cyclic voltammetry(CV).The electrochemical oxidation potentials (Φ

p

) and reduction potentials(Φ

n

) of these organic small molecular were measured by a 273A model potentiostat/galvanostat at a potential scan rate of 50 mV/s.In each measurement case

the organic small molecular film on a conducting glass substrate was used as the working electrode;platinum wire was used as counter electrode.All the potential values are referred to Ag/AgCl/Cl

-

as the reference electrode.The energy levels corresponding to the highest occupied molecular orbital(HOMO)

lowest unoccupied molecular orbital(LUMO) and energy gap(

E

g

) of these small molecules were determined from the onset potentials for oxidation (Φ

p

) and reduction(Φ

n

)

respectively

and HOMO energy level(

E

HOMO

)

LUMO energy level(

E

LUMO

) and

E

g

are calculated through following empiric formula

E

HOMO

=-e(Φ

p

+4.44)(1)

E

HOMO

=-e(Φ

n

+4.44) (2)

E

g

=-eΔΦ (3)Where ΔΦ=Φ

p

-Φ

n

e is elementary charge.The experimental values of the electrochemical energy gap of Alq

3

and its derivatives are in good agreement with the results determined by the optical absorption spectroscopy.The experimental values of

E

HOMO

E

LUMO

and

E

g

of Alq

3

are in excellent agreement with the values quoted from literatures.It was shown that the HOMO

LUMO energy level and E

g

obtained from CV measurements for these organic small molecular are feasible

and the measurement data obtained are reliable.In order to perfect organic light-emitting diodes the energy band structure parameters of electroluminescent materials are of critical important to the selection of cathode and anode materials.The recombination mechanisms of electrons and holes in these organic materials will be explained by using these energy level structure parameters.