Luminescence and Photoconductivity of Nitronaphthalenes

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Abstract

This work reports the first observation of phosphorescence from polycrystalline nitronaphthalenes. The phosphorescence spectrum, is red-shifted from its molecular counterpart; its relative intensity decreases as the temperature is increased from 77°K, exhibiting a relatively weak activation energy. The emission is attributed to triplet (π*← π) states whose lifetimes at room temperature are 35μ sec and 0.4μ sec for 1,5-dinitro-naphthalene and 1,8-dinitronaphthalene respectively. At room temperature in 1,5-dinitronaphthalene single crystal platelets, the photoconductivity observed is extrinsically generated, holes being more efficiently trapped than electrons, and is tentatively attributed to mobile excitons which migrate to the electrode and dissociate there producing holes and electrons.