PiSystems is a program for the quantumtheoretical calculation of conjugated molecules, highly useful for theoretical considerations prior to scientific laboratory work as well as for teaching students in chemistry.

PiSystems' specific features (see screenshots):

• Extremely fast and reliable algorithm for the calculation of the electronic ground and excitation states and absorption spectra

• Calculation of the colour and its solvent dependence

• Self-explanatory visualization of the electronic dynamics upon excitation

• Immediate, reliable prediction of the influence of substitution upon the absorption spectrum

• Reliable prediction of the molecule's reactivity and selectivity property towards electrophiles and nucleophiles

• Extremely simple, paper-and-pencil-like graphical molecule input

• No limit in number of atoms and bonds

• Atom and substituent parameters easily accessible and modifiable

• Each calculated molecule usable as input fragment for further calculations

• Extensive, context-sensitive online help