Luminescent furo[2,3-c]isoquinolines as fluorophores - Tuning the luminophore by donor substitution

A new library of the uncommon furo[2,3-c]isoquinoline scaffold has been synthesized by coupling the Ugi multicomponent reaction with a complex one-pot Pd-mediated double cyclization. The highly convergent and diversity-oriented approach has been exploited to introduce substituents with electron donor properties directly linked to the scaffold in the most representative positions 1 and/or 8. Moreover, the influence of an aromatic ring used as spacer between the scaffold and the electron donor substituent, as well as the substitution of the phenyl substituent in position 1 with a thiophene, on the photophysical properties have been investigated. Upon UV excitation part of the new molecules are intensively blue luminescent but for an amino donor substituent a significant switch to green emitters has been observed even upon eyesight. The electronic structure has been semiquantitatively rationalized by DFT and (TD)DFT calculations.