In the present work we simulate the transport properties and absorption spectra of the organic corn pound ethyl red This is the first theoretical study of a specific pH indicator utilized as nano device based on first principle quantum mechanics calculations and a non-diffusive transport model The charge dis tribution along the molecule is calculated via ab initio technique as a function of an external electric field Based on a resonant multilevel model we also calculate the current against bias voltage Both the charge accumulation and the current present similar behavior like resonant type conduction and asymmetric charge-voltage and current-voltage curves We also find an agreement between the theoretical absorption spectrum and experimental results for the zero bias regime Results for absorption spectra in several regimes under forward and reverse bias are analyzed Our main results suggest that the present system could operate as a bi directional molecular transistor (C) 2010 Elsevier Ltd All rights reserved