Phenol derivatives containing a proton acceptor site at an ortho position are able to undergo excited-state intramolecular proton transfer (ESIPT).  These derivatives isomerize from the enol form to the keto form upon photoexcitation, thereby allowing a four-level photophysical cyczwle––enol, enol*, keto*, and keto states.  The fluorescence from the keto* form has advantages of the large Stokes shift and lack of self-absorption, contributing to the efficient photoluminescence in the aggregated state.  In addition, the four-level cycle is suitable for the operation of low-threshold lasing.  On the other hand, ESIPT fluorophores often have a drawback of low fluorescence quantum yields (Φ_FL) in fluid media such as organic solvents and liquid crystals (LCs).  2-(2-Hydroxyphenyl)benzothiazole (HBT: Fig. 1), a representative ESIPT fluorophore, affords low Φ_FL values in solution (~0.01), which is rationalized by the nonradiative decay process triggered by the twisting of the central C–C bond in the excited state.  Here we demonstrate that a substitution of HBT with conjugated groups such as phenylene and ethynylene remarkably increases Φ_FL in solutions and LCs. These derivatives are highly miscible in LCs and amorphous polymers over 10 wt%, which enables the polarized luminescence, amplified spontaneous emission, and microcavity laser.  In this talk, rational molecular designs of not only ESIPT but also intramolecular charge transfer-based fluorophores will be introduced, featuring their excited-state planarization behavior.