A process for preparing substituted pentacene compounds comprises the step of cyclizing substituted bis(benzyl)phthalic acids using an acid composition comprising trifluoromethanesulfonic acid, the substituted bis(benzyl)phthalic acids being represented by the following general formulas: ##STR1##

wherein each R (that is, each of the groups R¹ through R⁸) is independently an electron-donating group, a halogen atom, a hydrogen atom, or a combination thereof.