Excited state dynamics in phthalocyanines studied using degenerate four wave mixing with incoherent light

Abstract

We present our experimental results on the measurements of excited state dynamics in phthalocyanines ( Pc , CuPc , FePc , and ZnPc ) using degenerate four wave mixing with incoherent light (DFWM-IL). Three different timescales were observed, for all samples, in the phase conjugate signal recorded as a function of delay in probe beam in the standard backward geometry. The fastest component (< 170 fs) is associated to the phase relaxation in the S n states and the slowest components (∼3-5 ps and 35-55 ps) to the vibration and population relaxation times from the S1 state. The present results are compared with those obtained with shorter pulses and various techniques for similar molecules. The consequences of such short lifetimes are also discussed in view of the strong optical limiting properties of these molecules.

Picosecond and nanosecond third order nonlinear optical characterization of Cu and Ni phthalocyanines using Z-scan technique

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Several groups have argued about nuances of these materials in extensive range of photonic applications. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Our comprehensive experiments and detailed modeling, along with the obtained nonlinear coefficients, strongly suggest that these molecules are potential molecules with large nonlinear coefficients in ns, ps, and fs time domains with ultrafast response times.…”

Phthalocyanines for photonic applications: a new perspective

“…The high stability and capability of phthalocyanines, especially, to accommodate different metal ions within their cavity result in diverse optical properties. Even though nonlinear optical properties of surplus of phthalocyanines and their derivatives [11][12][13][14][15][16][17][18][19][20][21][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] have been investigated till date to assess their performance for NLO applications there remains further scope for investigation of novel structures with superior figures of merit. The best optical limiting performance till date has been achieved using a phthalocyanine in tandem with another nonlinear optical material justifies the potential of these molecules [56].…”

Coherent control of biomolecules

“…Using degenerate four-wave mixing with incoherent light, Rao et al found three different time components [135], which were assigned to phase relaxation of S n states (<170 fs), vibrational relaxation (∼3-5 ps), and population relaxation from the S 1 to the ground state (35 ps). Again, such a fast relaxation from S 1 is unrealistic, considering the known fluorescence quantum yield and lifetime.…”

“…Several experimental studies on the photophysics of ZnPc and similar compounds (derivatives or different metallophthalocyanines) in solution have been reported [130][131][132][133][134][135][136][137][138][139][140][141], but so far the results fail to depict a coherent picture of the overall photophysics. The generally accepted energy-flow model includes three major intramolecular relaxation pathways from the initially excited S 1 state.…”

“…The S 1 lifetime of ZnPc in toluene is claimed to be ∼35 ps by Rao and co-workers, a value obtained by degenerate four wave mixing using incoherent light [135]. The setup used, however, was inadequate to quantify components exceeding 100 ps.…”