Singlet−Triplet and Triplet−Triplet Interactions in Conjugated Polymer Single Molecules

Abstract

Single molecule fluorescence correlation spectroscopy has been used to investigate the photodynamics of isolated single multichromophoric polymer chains of the conjugated polymers MEH-PPV and F8BT on the microsecond to millisecond time scale. The experimental results (and associated kinetic modeling) demonstrate that (i) triplet exciton pairs undergo efficient triplet-triplet annihilation on the <<30 micros time scale, (ii) triplet-triplet annihilation is the dominant mechanism for triplet decay at incident excitation powers > or =50 W/cm(2), and (iii) singlet excitons are quenched by triplet excitons with an efficiency on the order of (1)/(2). The high efficiency of this latter process ensures that single molecule fluorescence spectroscopy can be effectively used to indirectly monitor triplet exciton population dynamics in conjugated polymers. Finally, correlation spectroscopy of MEH-PPV molecules in a multilayer device environment reveals that triplet excitons are efficiently quenched by hole polarons.

Spin injection from ferromagnetic Co nanoclusters into organic semiconducting polymers

“…21 Secondly, the mutual intersystem conversion can occur through singlet-triplet crossing 15 or triplet-triplet annihilation. 23,24 We suggest that the consequence of the population redistribution is to reach an equilibrium, in which these three polaron-pair states of ͑PP͒ 1 m=0 , ͑PP͒ 3 m=0 , and ͑PP͒ 3 m=1 have equal fractions of 1 / 3, 1 / 3, and 1 / 3 prior to further relaxations ͓scheme 1͑a͔͒. Note that the capture of non spin-polarized electrons and non spinpolarized holes gives rise to four polaron-pair states: ͑PP͒ 1 m=0 , ͑PP͒ 3 m=0 , ͑PP͒ 3 m=1 , and ͑PP͒ 3 m=1 with equal populations of 1/4:1/4:1/4:1/4: ͓scheme 1͑b͔͒.…”

Stochastic Model of Photodynamics in Multichromophoric Conjugated Polymers

“…8 Thus, we set k isc ) 7 × 10 6 s -1 , k′ isc ) 2 × 10 3 s -1 , k q ) 6 × 10 8 s -1 , and τ fl ) 3 × 10 -9 s. We consider two limits of triplet-triplet annihilation: fast (k tt . k′ isc ) and slow (k tt , k′ isc ).…”

“…This technique can greatly minimize spectral and kinetic heterogeneity. To improve the signal-to-noise ratio in an emission transient, Barbara et al have developed two experimental approaches based on fluorescence intensity autocorrelation analysis 8 and, particularly fruitful, excitation intensity modulation. 9 The triplet dynamics is measured indirectly, by monitoring the relaxation of singlet fluorescence toward equilibrium on a time scale much longer than the singlet radiative lifetime, in response to a wide rectangular laser pulse of about 0.5 ms duration.…”

Low roll off radiation efficiency of charge transfer state excitons based on organic photovoltaic and electroluminescent integrated device

“…Thus, the high value of n SE was considered the major reason for the EQE SE roll off. As well known, the monomolecular and bimolecular quenching processes, and singlet or triplet polaron annihilation [24][25][26] were revealed as the intrinsic factor for the roll off of power efficiency and EQE SE of OPVCs, and the intrinsic reason for n SE higher than n 0 accordingly.…”