Energy and Electron Transfer in Ethynylene Bridged Perylene Diimide Multichromophores Cristina Flors, Ingo Oesterling, Tobias Schnitzler, Eduard Fron, Gerd Schweitzer, Michel Sliwa, Andreas Herrmann, Mark van der Auweraer, Frans C. de Schryver, Klaus Mullen, and Johan Hofkens J.Phys.Chem.C. 2007, 111, Kou ITOH MIYASAKA Lab.

Contents ● Background ● Method – explanation of measurement technique time-resolved spectroscopy (ensemble) single-molecule spectroscopy ● Results and discussion Steady-state measurement Florescence decay measurement Femtosecond transient absorption spectroscopy Single-Molecule detection ● Conclusion

Background Novel photonic devices consisting of molecular systems ● single photon source ● artificial light-harvesting system etc. single photon sourceartificial light-harvesting system light pulse Single photon light energy Chromophore : J.P.C.B.2004,108, J.A.C.S.2007,129,

Evaluation and understanding of the molecular photonic devices Ensemble measurementsSingle molecule measurements Energy transfer Electron transfer Emission lifetime etc. Dynamics, Efficiency of Ultra-high temporal resolution Reliable average values Emission dynamics of individual molecular systems Photon antibunching Enables us to evaluate single nanoscale photonic devices Complementary use of both measuring methods can give us comprehensive understanding of the nanoscale-molecular devices

Method 1): ensemble time-resolved measurement hν fluorescence S0S0 S1S1 Pump light T T: delay time Wavelength/nm Delta A Transient absorption spectra ① ② Probe light Charge separation Fluorescence decay count time/ns sample detector

Method 2): single-molecule spectroscopy imaging Fluorescence intensity trajectory counts Time/s Fluorescence decay counts Time/ns coincidence Events Delay/ns

Molecular structure of PDI derivatives Perylene-3,4,9,10- tetracarboxdiimide (PDI) :bay area Ａ B C ＰＤＩ０

Steady-state measurement Compound ABC λmax, abs,nm 573 λmax, emi,nm ΦF Summery of the photophysical properties of Ａ－Ｃ in solution in toluene in THF : Diphenylacetylene group(electron donor) A: black B: red C: blue (in toluene) Compound ABC λmax, abs,nm λmax, emi,nm ΦF scheme S1S1 S0S0 Charge Separation B A

Fluorescence decay measurement ABC Toluene τ F [ns] THF τ F [ns]1.0(14%) 2.8(86% ） B(THF) A(THF) C(THF) Ａ B t F : 1.0 ns t F ~ 2.8 ns Electron transfer from a diphenylacetylene group Through-space electron transfer ABC Toluene  [ns]  [ps] THF  [ns]  [ps] Fluorescence decay (time constant) Time-resolved fluorescence depolarization C oxygen nitrogen

Femtosecond transient absorption spectroscopy ① Transient absorption spectra in THF of PDI0(A) And B(B) at 2(black),10(red),50(green),100(blue) 200(purple),and 400ps(brown). PDI0 Compound B Lifetime ＰＤＩ０ B 5ns185ps,1ns S1S1 S0S0 Radical anion 1.1ns (Slide 9) 185ps 1ns

Summary of the ensemble measurements ABC Toluene ××× THF ○○ × Electron Transfer ● Femtosecond transient absorption measurement The dynamics of generation and decay about PDI radical anion was revealed. (in more polar solvent)

Single-Molecule measurement : Results ① Channel A Channel B Single-molecule intensity trace of Ａ in PMMA Channel A (gray) and B (black) correspond to Polarization directions perpendicular in each other. 1:stepwise change → the emitting chromophoric site is changing with time. 2:fluctuating trace → intersystem crossing from singlet to triplet by oxygen 3:off time → influence of charge separation APD2 APD1 fluorescence Beam splitter Off time

NCNC NLNL NLNL N C /N L ~ 0.2 APD2 APD1 Repetition period ~ 125ns APD1 APD2 Interphoton arrival time ： Photon Coincidence Single-photon emitting source 1 pulse → 1 photon Single-photon emitting source 1 pulse → 1 photon Antibunching J.P.C.B 2004,108, Jpn.J.Appl.Phys 2007,46, Single-Molecule measurement (Coincidence) N C /N L = 1 － ( 1 / M ) N C : number of central position N L : number of lateral positions M : number of photons / 1 pulse MN C /N L ratio Fluorescence from the sample sample

Single-Molecule measurement : results ② Compound A J.Phys,:.Condens.Matter. 2007,19, Fluorescence trajectory of single-molecule (A) and fluctuation of Nc/N L ratio S 1 -S 1 annihilation S 1 * + S 1 * → S o + S 1 * S０S０ S１S１ S０S０ S１S１ SｎSｎ

Conclusion The authors synthesized a multichromophoric system as a candidate for single photon source and measured the property of the emission. Steady state and time-resolved ensemble measurement revealed that charge transfer can take place in the multi-chromophoric compound in relatively polar environment; polarity affects the emission property of compound A. The time-resolved measurement also suggested that energy- migration as well as the charge transfer. The efficient energy migration was confirmed by measuring the photon-antibunching of compound; the compound worked as “single photon emitter”.