Singlet chain length dependence

The chain length dependence of the photophysical properties of oligofluorenes has been studied in detail. As the length increases, the energies of their fluorescence, phosphorescence, triplet-triplet absorption, and their fluorescent lifetime all decrease, while the magnitude of the transition dipole moment increases [154,155]. Furthermore, the triplet state was found to be only slightly more confined than the singlet state [155]. 

D. Beljonne, A.J. Ye, Z. Shuai, and J.L. Bredas, Chain-length dependence of singlet and triplet exciton formation rates in organic light-emitting diodes, Adv. Fund. Mater., 14, 684-692 (2004). 

Dorr, Lewis, and co-workers found evidence through quenching experiments and flash spectroscopy for a triplex in the system trans-stilbene — amine — benzene — [105]. They quenched singlet excited trans-stilbene with various mono- and diamines and found a steric effect on the quenching constant The a, co-diamines (dabco, diaminoethane, -propane and -butane) quenched the stilbene fluorescence more efficiently than the monoamines, depending on the chain length between the amino groups. This was ascribed to the formation of cyclic radical cations, with a N-N three electron a-bond. In this case, an exciplex between diamine and stilbene is formed. 

A series of n-alkylbenzenes, cooled by supersonic expansion and excited to what are initially well localized ring distortion vibrations within the first excited singlet states, show fluorescence spectral behaviour that is dependent upon the alkyl chain length. For the first three members of the series (toluene to n-propylbenzene) resonance fluorescence from the initially pumped mode in 5, was observed, but for... 

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