The possibility of overcoming the Shockley–Queisser limit of organic solar cell (OSC) efficiency by multiexciton generation through singlet exciton fission has recently attracted significant research interest. Herein we show that 9,10-bis­(phenylethynyl)­anthracene (BPEA), an ethynyl derivative of anthracene and a widely used fluorescence molecular probe, exhibits an efficient singlet exciton fission process in the solid state. Steady state and time-resolved emission experiments carried out on a nanoaggregate and thin film of BPEA reveals an orders-of-magnitude reduction in emission yields and the singlet lifetime as compared to the near-unity emission yield and long emission lifetime in solution. Femtosecond and nanosecond resolved transient absorption studies unraveled exciton–exciton annihilation (at high excitation fluence) and singlet exciton fission to be the dominant relaxation processes with a fission yield of about 74 ± 6%. A high singlet fission yield with a long triplet lifetime (of about 30 μs) of BPEA in thin films and aggregates makes this material an interesting candidate for further study in OSC applications.

Wavenumber (cm -1 ) Absorption spectrum Excitation Spectrum (λ em = 425 nm) 400 380 360 340 320 Wavelength (nm)

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Effect of morphology and influence of two phenyl rings at 9 and 10 position of anthracene on exciton and excimer relaxation dynamics in solid state has been presented.