Electronic Polarization Reversal and Excited State Intramolecular Charge Transfer in Donor/Acceptor Ethynylpyrenes

An attempt to tune the electronic properties of pyrene (Py) by coupling it with a strong electron donor (−PhNMe2, DMA)/acceptor (anthronitrile, AN) through an ethynyl bridge has been undertaken. A moderate electron donor (iPrOPh−, IPP)/acceptor (2-quinolinyl, 2Q) has also been incorporated, and all four molecules were studied with reference to a neutral molecule, namely, 1-phenylethynylpyrene (PhEPy). All the arylethynylpyrenes (ArEPy's) have been thoroughly characterized, and their electronic properties were studied by absorption and emission spectral properties of these ArEPy's. The electrochemical characteristics were also studied for arriving at the electrochemical band gap which has been compared with the HOMO−LUMO energy gap derived from the photophysical measurements and theoretical calculations performed by density functional theory (DFT) using B3LYP/6-31G* basis sets. The results obtained from experimental and theoretical studies are critically discussed.