Methodology and basis set for study in UV-Vis

I am currently working with a system of 30 atoms of a organic molecule. I need to make a study related to determine the UV-Vis graphic as precisely as possible. 


I am using DFT method. However, I am having trouble to find a methodology and basis set to obtain a proper result of the experiment.


Does anybody know what methodology and basis set I should use?


P.S: I have already tried B3LYP with 6-31G(d), 6-31G(d,p) and 6-311++G(2d, 2p) in sequence but the results weren't good.


