To design near-infrared (NIR) absorbing polyaromatic dyes, we have theoretically elucidated the electronic transition properties of the extended π-conjugation derivatives of 3,4,9,10-perylenetetracarboxylic dianhydride diimide (PTCAI). Framework extension along the molecular long axis, that is, to terrylene (TTCAI) and quaterrylene (QTCAI), causes a large bathochromic shift by the narrowing of the HOMO-LUMO gap. Despite the larger π-conjugation, framework expansion along the molecular short axis, that is, to benzo[g,h,i]perylene (bPTCAI) and coronene (CTCAI), causes a hypsochromic shift. Framework extension along the molecular long axis is a beneficial guiding principle of the NIR dye design. To design new polyaromatic chromophores, although the electronic transition properties are roughly determined by the core aromatic structure, we must consider the whole molecule because the modified part plays an important role in controlling the advanced properties.