Dicyanomethylenated Diaryldihydropentalenediones that Vary Excited State Decay Rates without Changing Emission Wavelengths

Abstract

2-(3,6-Bis(4-methoxyphenyl)-2,2,5,5-tetramethyl-4-oxo-4,5-dihydropentalen-1(2H)-ylidene)malononitrile (DPM-An) and 2,2′-(3,6-bis(4-methoxyphenyl)-2,2,5,5-tetramethyl-2,5-dihydropentalene-1,4-diylidene)dimalononitrile (DPD-An), both bearing the 2,5-dihydropentalene core and intramolecular electron donor–acceptor moieties, were prepared and subjected to photophysical studies. The absorption spectra of DPM-An and DPD-An in CH₂Cl₂ at room temperature contain maxima at similar wavelengths of 406 and 409 nm, respectively. These substances do not luminesce in CH₂Cl₂ solution at room temperature, but they do emit light when present in poly(methyl methacrylate) films. Interestingly, DPM-An and DPD-An in the film forms display nearly identical emission (EM) spectra with respective maxima at 592 and 594 nm. In contrast, DPD-An has a longer EM lifetime than does DPM-An. Therefore, the dihydropentalene derivatives, exemplified by DPM-An and DPD-An, may be a family of substances in which excited state decay rate can be varied without changing EM wavelengths.