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▲ [14p-2D-4] Interplay between Förster energy migration and defect concentration in shaping a photochemical funnel in PPV
Keywords:Photochemical funneling,Conjugated Polymers,Excitation population dynamics
Single molecule experiments have suggested the existence of a photochemical funnel in the photophysics of conjugated polymers, like poly[2-methoxy-5-(20-ethylhexyl)oxy-1,4-phenylenevinylene] (MEH-PPV). The conformational or chemical defects along the polymer chain leads to length distribution of chromophores along the polymer chain [1, 2]. Efficient non-radiative energy transfer among these chromophore segments is considered to be the origin of photochemical funnel [3, 4]. To study the excitation energy dynamics along PPV, we modelled PPV chain as a polymer with the length distribution of chromophores given either by a Gaussian or by a Poissonian distribution. We observe that the Poisson distribution of the segment lengths explains the photophysics of PPV better than the Gaussian distribution. An extended ‘particle-in-a-box’ model is used to calculate the exciton energies and the transition dipole moments of the chromophores, and a master equation to describe the excitation energy transfer among different chromophores. The rate of energy transfer within first approximation is assumed to be given by the well-known Förster expression [5]. The observed excitation population dynamics confirms the photochemical funneling of excitation energy from shorter to longer chromophores of the polymer chain. However, we find that the excitation energy may not always migrate towards the longest chromophores in the polymer chain instead there exist local domains in the polymer chain within which the non-radiative energy transfer from shorter to longer chromophores take place. These results are found to be in agreement with the experimental reports [6, 7]. The time scale of spectral shift and energy transfer for our model polymer, with realistic values of optical parameters, is in the range of 200–300 ps.
References:
[1] D. Hong, J. Hu, B. Bagchi, P. Rossky and P. Barbara, Nature 405, 1030 (2000).
[2] K. F. Wong, M. S. Skaf, C. Yang, P. J. Rossky, B. Bagchi, D. Hu, J. Yu and P. F. Barbara, J. Phys. Chem. B 105, 6103 (2001).
[3] B. Bagchi, Annu. Rep. Prog. Chem., Sect. C: Phys. Chem 109, 36 (2013).
[4] S. Saini and B. Bagchi, Phys. Chem. Chem. Phys. 12, 7427 (2010).
[5] B. Bagchi, "Molecular Relaxation in Liquids" (Oxford, NY, 2012).
[6] V.V. N. R. Kishore, S. Kokane, K. L. Narasimhan and N. Periasamy, Chem. Phys. Lett. 386, 118 (2004).
[7] H. Lin, S. R. Tabaei, D. Thomsson, O. Mirzov, P.-O. Larsson and I. G. Scheblykin, J. Am. Chem. Soc. 130, 7042 (2008).
References:
[1] D. Hong, J. Hu, B. Bagchi, P. Rossky and P. Barbara, Nature 405, 1030 (2000).
[2] K. F. Wong, M. S. Skaf, C. Yang, P. J. Rossky, B. Bagchi, D. Hu, J. Yu and P. F. Barbara, J. Phys. Chem. B 105, 6103 (2001).
[3] B. Bagchi, Annu. Rep. Prog. Chem., Sect. C: Phys. Chem 109, 36 (2013).
[4] S. Saini and B. Bagchi, Phys. Chem. Chem. Phys. 12, 7427 (2010).
[5] B. Bagchi, "Molecular Relaxation in Liquids" (Oxford, NY, 2012).
[6] V.V. N. R. Kishore, S. Kokane, K. L. Narasimhan and N. Periasamy, Chem. Phys. Lett. 386, 118 (2004).
[7] H. Lin, S. R. Tabaei, D. Thomsson, O. Mirzov, P.-O. Larsson and I. G. Scheblykin, J. Am. Chem. Soc. 130, 7042 (2008).