Transient photocurrents induced by time‐dependent diffusion of excitons to the surface of anthracene and p‐chloranil single crystals

Transient photocurrents produced by a light flash were used as a probe for the time‐dependent diffusion of excitons in anthracene and p‐chloranil single crystals. An analytical solution for the time‐dependent diffusion equation for excitons near a quenching phase boundary is presented. Inserting experimental data allows evaluation of the lifetime, τ = 4×10−6s, the diffusion coefficient, D = 5×10−6 cm2/s, and hence the diffusion length, L = 5×10−6 cm, for n‐π* triplet excitons diffusing perpendicular to (ab) planes in p‐chloranil. For triplet excitons in anthracene, the diffusion coefficient normal to (ab) plane, D ≈ 5 × 10−5 cm2/s, is estimated. The method allows to distinguish between different sorts of excitons diffusing in a crystal with different velocities. This is of importance for anthracene, where both singlet and triplet excitons are produced by strongly absorbed light.