ContentsIntroduction

Optical limiters and Reverse Saturable Absorption

ChromophoresPorphyrinsPhthalocyaninesFullerenes

Optical Limiting Studies

Conclusion

IntroductionLasers are used in: CD players, scanners, laser pointers, spectroscopic studies, optical sensors, astronomy, military, etc.

Damages skin tissues and causes blindness.Smart materials transparent under ordinary ambient light conditions, but can absorb or block intense laser light over a broad wavelength range.

Development of optical limiting materials that rely on reverse saturable absorption.

Optical Limiting MaterialsNonlinear optical materials whose transmittance decreases significantly with increasing light fluence.

Beyond the threshold, the flux of photons remains constant.

Output fluenceInput fluencethresholdLinear transmittanceidealreal

Physical processes causing optical limiting effects AbsorptionRefractionReflectionScatteringS

One photon absorptionSnGkisckSGkTG = absorption cross section

Five-level energy diagramSequential Two photon absorptionExcited state which could absorbST

Dependence on the laser pulseShorter pulse durationLonger pulse duration

Dependence on the laser pulseTnT1kiscGS1SnEGkSGSShorter pulse durationLonger pulse durationXThree-level energy diagram

Dependence on the laser pulseGS1SnTnT1EGkisckSGkTGSTShorter pulse durationLonger pulse durationGS1SnEGkSGSThree-level energy diagramFour-level energy diagram

Reverse Saturable Absorption (RSA)The excited state cross section is larger than the ground state cross section.

S/G > 1 (or) T/G > 1

Materials showing RSA become more opaque upon exposure to light of suitable wavelength.TnT1

Reverse Saturable Absorption vs. Two Photon Absorption

Criteria for Optical LimitingSequential TPA, ES > G.

ES > the pulse duration.

Wide range of incident intensities.

Low threshold.

Large non linear absorption over a broad spectral bandwidth.

ES / G ratio.

Saturation fluence.

Reverse Saturable Absorber ChromophoresOrganic Molecules

Reverse Saturable Absorber Chromophores

Techniques usedZ-scan Technique

Output vs. input fluence

Transmission vs. input energyOutput fluenceInput fluenceInput energyTransmission

Porphyrins and Phthalocyanines

Porphyrins and PhthalocyaninesVersatility, architectural flexibility, high thermal and environmental stability, inexpensiveness, non-toxicity and ease of processing.

Tailoring the electronic properties:70 different metal atomsSubstitution on the ringAxial substitution

Porphyrins: Early studies 80ps pulse delayTetraphenyl porphyrinsBlau, W.; Byrne, H.; Dennis, W. M.; Kelly, J. M. Opt. Commun. 1985, 56, 25 Fast ISC due to heavy atom effect

MoleculefG (10-17 cm2)S/GT/GH2TPP9 ns1.63.8S1 SnCoTPP

Effect of metal centre and meso substituentNd:YAG laser: 532nmPulse delay: 80ps, 14ns McEwan. K. J.; Bourhill. G.; Robertson. J. M.; Anderson. H. L. Journal of Nonlinear Optical Physics & Materials, 2000. 9, 451

Q- bands are red-shifted through 2H, Zn and Pb. Pb derivatives are better optical limiters.McEwan. K. J.; Bourhill. G.; Robertson. J. M.; Anderson. H. L. Journal of Nonlinear Optical Physics & Materials, 2000, 9, 451

G 10-17 cm2S 10-17 cm2T 10-17 cm2TTP (H)1.714.02.5TTP (Zn)3.077.34.1TTP (Pb)0.63-6.7TTMSAP (H)1.918.35.9TTMSAP (Zn)0.581718TTMSAP (Pb)0.53-24

Effect of conjugationQureshi, F. M.; Martin, S. J.; Long, X.; Bradley, D. D. C.; Henari, F. Z..; Blau, W. J.; Smith, E. C.; Wang, C. H.; Kar, A. K..; Anderson. H. L. Chemical Physics, 1998, 231, 87% transmittance:60%, 40% and 35%exc = 532nmpulse delay: 500psGreater the conjugation, the better is the optical limiting performance.

Indium PhthalocyaninesBulky groups enhances optical limiting performances.Dini, D.; Barthel, M.; Hanack, M. Eur. J. Org. Chem. 2001, 3759exc = 532nmpulse delay: 5nsEffect of - and axial- substituents

Indium NaphthalocyaninesOptical limiting properties: similar to InPcsIncrease in solubility.Q-band red shifts to ~800nmInPcs: Optical limiter in blue regionInNcs: Optical limiter in red regionDini, D.; Barthel, M.; Hanack, M. Eur. J. Org. Chem. 2001, 3759

Effect of Axial SubstitutionEWG on axial position improve the optical limiting performances.Dini, D.; Barthel, M.; Hanack, M. Eur. J. Org. Chem. 2001, 3759Titanium Phthalocyaninesexc = 532nmpulse delay: 5ns

Heavy Atom EffectAuger, A.; Blau, W., J.; Burnham, P. M.; Chambrier, I.; Cook, M. J.; Isare, B.; Nekelsona, F.; OFlaherty, S. M. J. Mater. Chem. 2003, 13, 10421,4,8,11,15,18,22,25-octaalkylphthalocyanines

Heavy central atom: better optical limiting responseAuger, A.; Blau, W., J.; Burnham, P. M.; Chambrier, I.; Cook, M. J.; Isare, B.; Nekelsona, F.; OFlaherty, S. M. J. Mater. Chem. 2003, 13, 1042

Im[(3)] (esu)R = n-C6H131M = H, H(6.6 1.3) x 10-126M = Zn(1.5 0.3) x 10-11R = n-C10H212M = H, H(5.8 1.1) x 10-127M = Zn(9.1 1.8) x 10-12

Effect of - and axial- substituentsThe absence of any group with strong electronic character in Ar substituents:small decreases of transmittance.high threshold intensity value.Vagin, S.; Barthel, M.; Dini, D.; Hanack, M.; Inorg. Chem. 2003, 42, 2683

Gallium DerivativesF atoms increases solubility. 8 is a better optical limiter.Yang, G. Y.; Hanack, M.; Lee, Y. W.; Chen, Y.; Lee, M. K., Y.; Dini, D.; Chem. Eur. J. 2003, 9, 2758.exc = 532nmpulse delay: 5ns

Polypyridyl PorphyrinsDuncan, T. V.; Rubtsov, I. V.; Uyeda, H. T.; Therien, M. T. J. Am. Chem. Soc. 2004, 126, 9474Pulse delay = 1ns

(nm)(G.S.) (nm)(E.S.)T (s)E/GRuPZn6388844475OsPZn6409640.86163RuPZnA68293124227OsPZnA7049851.08135RuPZnOs7101000.079324

Fullerenes

Fullerenes: Early studiesTutt and Kost (1992): C60 in toluene solution is an excellent optical limiter.

C70, C76 , C78 and C84 have also been investigated.

C60 is by far the best in fullerene family.Tutt, L. W.; Kost, A. Nature, 1992, 356, 225.

Range of interest: 600nm-near IRTriplet-triplet absorption

Solvent DependenceSolvent independent, but varies in solvents containing EDG.

N,N-diethylaniline (DEA) or N,N-dimethylaniline (DMA): Inter-molecular electron transfer.C60 + h C60*C60* + DEA (C60-DEA)* C60 + DEA+Ghosh, H. N.; Pal, H.; Sapre, A. V.; Mittal, J. P. J. Am. Chem. Soc. 1993, 115, 11722.

Medium DependenceWeaker responses in polymethylmethacrylate (PMMA) or poly(propionylethyleneimine) (PPEI) or sol-gel glasses.

Medium Viscosity dependent.Kost, A.; Tutt, L.; Klein, M. B.; Dougherty, T. K.; Elias, W. E. Opt. Lett. 1993, 18, 334.

Fullerene derivatives Derivatization increases the solubility in various solvents and eases polymerization.151617Sun, Y.-P.; Riggs, J. E. Chem. Mater. 1997, 9, 1268

Similar optical limiting efficiencies of C60 and its derivatives.Sun, Y.-P.; Riggs, J. E. Chem. Mater. 1997, 9, 1268

Multiple-functionalized methano-C60 dicarboxylates Optical limiting responses of the multiple functionalized methano-C60 dicarboxylates are all weaker than those of the parent C60 and the mono-functionalized derivatives.532nm5ns

C60-polystyrene polymersThe optical limiting responses of pendant polymers are weaker than those of C60 or the model compounds.Sun, Y. -P.; Lawson, G. E.; Huang, W.; Wright, A. D.; Moton, D. K. Macromolecules, 1999, 32, 3747.

Optical limiting mechanismIs Reverse Saturable Absorption the only mechanism?

Optical limiting performances in solid matrix different from that in solution?

FactorsMedium viscosityConcentration of C60

As viscosity and concentration increases, the system has a weak optical limiting property.

Bimolecular processes ?

Bimolecular processesSelf quenchingAnnihilationExcimer-like stateRiggs, J. E.; Sun, Y.-P., J. Phys. Chem. A. 1999, 103, 485.

Modified reverse saturable absorption modelRiggs, J. E.; Sun, Y.-P., J. Phys. Chem. A. 1999, 103, 485.

Phthalocyanine-fullerene derivativeCuPc-C60 is better optical limiter than CuPc or C60 itself.Zhu, P.; Wang, P.; Qiu, W.; Liu, Y.; Ye, C.; Fang, C.; Song, Y. Appl. Phys. Lett. 2001, 78, 1319.

Carbon OnionsExcimer laser: 308nm, 20nsUV-400 nitrogen laser: 337nm, 8nsNd:YAG laser: 532 and 1064nm, 12nsGeorgakilas, V.; Guldi, D. M.; Signorini, R.; Bozio, R.; Prato, M. J. Am. Chem. Soc. 2003, 125, 14268-14269

ConclusionOptical limiting materials rely on the phenomenon of reverse saturable absorption.

Porphyrins, phthalocyanines, naphthalocyanines and fullerenes are good candidates in the visible-near IR range.

Become more opaque upon exposure to light of suitable wavelength and hence could be used to protect eye or optical sensors from the intense laser source.

AcknowledgementProf. Russell H. Schmehl

Dr. D. KumaresanHeidi HesterSrivathsa VaidyaKalpana ShankarDavid KaramMonica Posse

The Chemistry Department, Tulane University

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Draw in chem draw two separate energy level diagramsDraw in chem draw two separate energy level diagramsDraw in chem draw two separate energy level diagramsDraw in chem draw two separate energy level diagramsCarbon nanotubesCheck the excitation wavelength from scifinderIs Ph ring perpendicular in TTPGroup the plot and the numbers, check the ref 109, 121,122, 124 for this from Sun reviewGroupCheck ref 132, Riggs and Sun 1999