Synthesis of asymmetric indolonaphthyridines with enhanced excited state charge-transfer character

Indolonaphthyridines (IND) are valuable chromophores with wide-ranging optoelectronic applications. Here, we present a new class of asymmetric IND derivatives, synthesised using novel high yielding methodology. We compare the absorption properties and excited state charge-transfer character of the novel assymetric INDs with symmetric IND. We show IND assymetry increases the change in dipole moment from ground to excited state. By determining the magnitude of the excited state dipole moment of each IND derivative, we also show assymetry increases excited state charge-transfer character. Quantum calculations indicate this is a consequence of increased spatial separation between excited state electron and hole wavefunctions for the assymetric INDs. Charge-transfer features can significantly benefit many optoelectronic processes, therefore the structure-property relationships introduced in this work provide invaluable design principles for the generation of high performance materials. We present the synthesis of novel asymmetric indolonaphthyridines with enhanced excited state charge-transfer character relative to symmetrical indolonaphthyridine.