This study represents an empirical model of cytosine-based optical molecular switch. This possible biomolecular switch has been designed using the first principle approach which is based on density functional theory and non-equilibrium Green's function. The quantum-ballistic transport property and current-voltage (I-V) characteristics of cytosine-based optomolecular switch have been investigated at 25 THz operating frequency. The influence of highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps on the electronic transmission and I-V characteristics has been discussed in detail. The aim of this study is to highlight the minimum conformational change during a single ON-OFF switching cycle. The biomolecule comprises switching behaviour when converts from straightened to twisted form during photo-excitement. The straightened and twisted forms of the molecule are represented as logic '0' and logic '1', respectively. This p and n regions of this switch has been made using electrical doping process. The current through the twisted form of the cytosine biomolecule is ∼1000 times higher than the straightened form. The maximum switching ratio 62.1 is obtained at 1 V bias. The origin of the switching behaviour of the biomolecule can be interpreted by quantum-ballistic transport model along with HOMO-LUMO gaps.