Diarylpyrenes vs. diaryltetrahydropyrenes: Crystal structures, fluorescence, and upconversion photochemistry

The synthesis of two series of substituted 2,7-diaryl-4,5,9,10-tetrahydropyrenes (1a–c) and 2,7-diarylpyrenes (2a–c) is reported; the opposing phenyl tips being terminated with tBu (a), OCH3 (b), or F (c) to impart variation in electronic properties. X-ray crystallographic analysis of the six compounds revealed edge-to-face packing predominately due to van der Waals forces in the solid state in all instances. The photophysical properties of these compounds were investigated in solution and in solid state/thin films. Since the 2,7-bis(4-tert-butylphenyl)tetrahydropyrene 1a possesses unity fluorescence quantum efficiency, it was successfully employed as the emitter in a low power upconversion scheme featuring fac-Ir(ppy)3 [ppy = 2-phenylpyridine] as the photosensitizer.