Distance from Esfahan to Tehran is 451 Km.
Almost is 5 hours to travel by car.
But the airport "Mehrabad" Tehran to Esfahan done daily flights, flight duration is forty five minutes.
For a road trip by bus from south Terminal can use "Ta'avoni" they are mentioned below.

Name Telephone
Ta'avoni 4 east
55185334-40 - 55185613-4
Ta'avoni 4 west
02144654651 - 02144630005 - 02144666030
Ta'avoni 7
02144662927  - 02144644599 - 02144660091
Ta'avoni 17
02155185415  - 02155185416 - 02155185422
Ta'avoni 6
02155185351