Frank C. Spano
B.S. (1982), Lehigh University
Computational / Photonics / Physical
Optical Excitations in Conjugated Oligomer and Polymer Aggregates and Films
Optical excitations in polymers and polymer films is a robust field, with progress and advances fueled by the promising commercial applications of polymer-based or plastic optical devices such as organic light-emitting diodes. Despite an enormous amount of primarily experimental research, there are significant gaps in our understanding of how such devices absorb and emit light. The goal of this research is to unravel the influences of intermolecular or excitonic interactions, exciton-vibrational coupling and structural defects on linearly and circularly polarized absorption, photoluminescence and electroluminescence in oligomer and polymer aggregates. The current focus is on aggregates, films and crystals of polyarenes as well as substituted and unsubstituted oligomers of poly-p-phenylene vinylene (PPV), and poly-thiophene (PT), among the best candidates for optical device applications. Theoretical techniques are being developed to treat weak to strong exciton-phonon coupling involving several electronic transitions and several intramolecular vibrational modes in two dimensional herringbone and lamellar aggregates as well as one-dimensional chiral aggregates, which contain point and structural defects. The influence of intermolecular modes (lattice phonons) are also of interest in establishing temperature dependent properties. The methods developed to date have proved successful in explaining several unusual spectral features of tetracene  quaterthiophene  and distyrylbenzene [3-7] nanoaggregates, and have predicted a "recipe" for superradiant DSB aggregates . Extensions to aggregates of larger oligomers and polymers are currently in progress. Plans are also underway to treat aggregates of cyano derivatives of oligo-phenylene vinylenes which have a layered packing arrangement promoting the formation of excimers.
The ability to align or orient molecular species prior to reaction is one of the main goals in the field of chemical reaction dynamics. In a successful collaboration with A. Marjatta Lyyra in the Physics Department, our research groups investigated electromagnetically induced transparency in diatomic lithium, leading to a novel method for measuring transition dipole moments . We also developed and demonstrated a three laser excitation scheme to selectively excite a target mJ level within a rovibronic level of a diatomic molecule . This is equivalent to alignment of the angular momentum vector. My group is responsible for developing the theoretical machinery needed to predict new excitation schemes. The theory is based on equations of motion which describe how the multilevel molecular density matrix evolves under the influence of two or more laser fields. The theory has successfully predicted full mJ resolution in the three laser experiment  and is currently being applied to more general problems involving the control and manipulation of molecular eigenstates via a strong coupling laser.
 J. Qi, F. C. Spano, T. Kirova, A. Lazoudis, J. Magnes, L. Li, L. M. Narducci, R. W. Field, and A. M. Lyyra, “Measurement of Transition Dipole Moments in Lithium Dimers Using Electromagnetically Induced Transparency”, Phys. Rev. Lett., 88, (2002).
 J. Qi, G. Lazarov, X. Wang, L. Li, L. M. Narducci, A. M. Lyyra and F. C. Spano, "Autler-Townes Splitting in Molecular Lithium: Prospects for All-Optical Alignment of Nonpolar Molecules", Phys. Rev. Lett. 83 288 (1999).
 F. C. Spano, "Theory of Sub Doppler Autler-Townes Splitting in Molecules: Alignment and Orientation of the Angular Momentum in Nonpolar Molecules", J. Chem. Phys. 114, 276 (2001).
Yamagata, H.; Pochas, CM.; Spano, FC. "Designing J- and H-Aggregates through Wave Function Overlap Engineering: Applications to Poly (3-hexylthiophene)." Journal of Physical Chemsitry B 116 (49): 14495-14503 (2012).
Yamagata, H.; Spano, FC. "Interplay between interchain and interchain interactions in semiconducting polymer assemblies: The HJ-aggregate model." Journal of Chemical Physics 136 (18): 184901 (2012).
Bobbert, PA.; van Dijk, L.; Spano, FC. "Theory of exciton dynamics in molecular aggregates in presence of polaronic effects." Chemical Physics Letters 529, 69-73 (2012).
Niles, ET.; Roehling, JD.; Yamagata H.; Wise, AJ.; Spano, FC.; Moule, AJ.; Grey, JK.;"J-Aggregate Behavior in Poly-3-hexylthiophene Nanofibers." Journal of Physical Chemistry Letters 3 (2): 259-263 (2012).
Kistler, KA.; Pochas, CM.; Yamagata, H.; Matsika, S.; Spano, FC. "Absorption, Circular Dichroism, and Photoluminescence in Perylene Diimide Bichromophores: Polarization-Dependent H- and J-Aggregate Behavior." Journal of Physical Chemistry B 116 (1): 77-86 (2012).
Tempelaar, R.; Stradomska, A.; Knoester, J.; Spano, FC. "Circularly Polarized Luminescence as a Probe for Long-Range Interactions in Molecular Aggregates." Journal of Physical Chemistry B 115 (36) 10592-10603 (2011).
Yamagata, H.; Spano, FC. "Vibronic Coupling in Quantum Wires: Applications to Polydiacetylene." Journal of Chemical Physics 135(5), 054906 (2011).
Yamagata, H.; Norton, J.; Hontz, E.; Olivier, Y.; Beljonne, D.; Bredas, JL.; Silbey, RJ.; Spano, FC. "The Nature of Singlet Excitons in Oligoacene Molecular Crystals." Journal of Chemical Physics 134(20), 204703 (2011).
Spano, FC.; Yamagata, H. "Vibronic Coupling in J-aggregates and Beyond: A Direct Means of Determining the Exciton Coherence Length from the Photoluminescence Spectrum." Journal of Physical Chemistry B 115(18):5133-5143 (2011).
Spano, FC.; Silvestri, L. "Multiple mode exciton-vibrational coupling in H-aggregates: Synergistic enhancement of the quantum yield". Journal of Chemical Physics 132 (9): 094704 (2010).
Spano FC. "Spectral Signatures of Frenkel Polarons in H- and J-Aggregates". Accounts of Chemical Research 43 (3):429-439 (2010).
van Dijk, L.; Bobbert, PA.; Spano, FC. "Extreme Sensitivity of Circular Dichroism to Long-Range Excitonic Couplings in Helical Supramolecular Assemblies." Journal of Physical Chemistry B 114 (2): 817-825 (2010).
Silvestri, L.; Tavazzi, S.; Spearment, P.; Spano, FC. "Exciton-phonon coupling in molecular crystals: Synergy between two intramolecular vibrational modes in quarterthiophene single crystals". Journal of Chemical Physics 130 (23): 234701 (2009).
Clark, J.; Change, JF.; Spano, FC.; "Determining exciton bandwidth and film microstructure in polythiophene films using linear absorbtion spectroscopy". Applied Physics Letters 94 (16): 163306 (2009).
Spano, FC. "Analysis of the UV/Vis and CD Spectral Line Shapes of Caroteniod Assemblies: Spectral Signatures of Chiral H-Aggregates". Journal of American Chemical Society 131 (12): 4267-4278 (2009).