On the other hand, two HBO derivatives, HBOCE and HBODC, which have an electron-withdrawing group in the 6-position exhibited the latter type of ESICT-ESIPT coup¬ling.45 Compared to the nitrogen atom of alkyl amine in DE-3HF, the electron-donating strength of the imino nitrogen atom of the benzoxazole ring is negligible because its lone pair electrons are involved in forming the π-electron aromatic resonance. After the ESIPT process upon photoexcitation, the imino nitrogen atom, however, is converted into an amino-nitrogen which can act as a strong electron donor, triggering the strong push-pull ICT interaction. Therefore, in this system, ESIPT occurs prior to ESICT, followed by a solvent relaxation of charge transferred keto form (K* CT). As a result, a strong solvatochromism in the K* CT emission band was observed, whereas the E* emission band was independent of solvent polarity