Communication: Tailoring the optical gap in light-harvesting molecules.

Systematically varying the optical gap that is associated with charge-transfer excitations is an important step in the design of light-harvesting molecules. So far the guidance that time-dependent density functional theory could give in this process was limited by the traditional functionals' inability to describe charge-transfer excitations. We show that a nonempirical range-separated hybrid approach allows to reliably predict charge-transfer excitations for molecules of practically relevant complexity. Calculated absorption energies agree with measured ones. We predict from theory that by varying the number of thiophenes in donor-acceptor-donor molecules, the energy of the lowest optical absorption can be tuned to the lower end of the visible spectrum. Saturation sets in at about five thiophene rings.

[1]  L. Kronik,et al.  Orbital-dependent density functionals: Theory and applications , 2008 .

[2]  R. Baer,et al.  A well-tempered density functional theory of electrons in molecules. , 2007, Physical chemistry chemical physics : PCCP.

[3]  A. Warshel,et al.  Calculations of Hydration Entropies of Hydrophobic, Polar, and Ionic Solutes in the Framework of the Langevin Dipoles Solvation Model , 1999 .

[4]  Burke,et al.  Generalized Gradient Approximation Made Simple. , 1996, Physical review letters.

[5]  Kieron Burke,et al.  Time-dependent density functional theory: past, present, and future. , 2005, The Journal of chemical physics.

[6]  Dmitrij Rappoport,et al.  Photoinduced intramolecular charge transfer in 4-(dimethyl)aminobenzonitrile--a theoretical perspective. , 2004, Journal of the American Chemical Society.

[7]  René A. J. Janssen,et al.  Synthesis and photovoltaic performance of a series of small band gap polymers , 2009 .

[8]  Benjamin G. Janesko,et al.  Generalized gradient approximation model exchange holes for range-separated hybrids. , 2008, The Journal of chemical physics.

[9]  S. Jenekhe,et al.  Phthalimide-based polymers for high performance organic thin-film transistors. , 2009, Journal of the American Chemical Society.

[10]  M. Mundt,et al.  Derivative discontinuities in time-dependent density-functional theory. , 2005, Physical Review Letters.

[11]  Zhihua Chen,et al.  Naphthalenedicarboximide- vs perylenedicarboximide-based copolymers. Synthesis and semiconducting properties in bottom-gate N-channel organic transistors. , 2009, Journal of the American Chemical Society.

[12]  A. Facchetti,et al.  A high-mobility electron-transporting polymer for printed transistors , 2009, Nature.

[13]  N. Handy,et al.  A new hybrid exchange–correlation functional using the Coulomb-attenuating method (CAM-B3LYP) , 2004 .

[14]  G. Scuseria,et al.  Hybrid functionals based on a screened Coulomb potential , 2003 .

[15]  Trygve Helgaker,et al.  Excitation energies in density functional theory: an evaluation and a diagnostic test. , 2008, The Journal of chemical physics.

[16]  Shawn T. Brown,et al.  Advances in methods and algorithms in a modern quantum chemistry program package. , 2006, Physical chemistry chemical physics : PCCP.

[17]  N. Maitra,et al.  Undoing static correlation: long-range charge transfer in time-dependent density-functional theory. , 2005, The Journal of chemical physics.

[18]  Hans-Joachim Egelhaaf,et al.  Optical Bandgaps of π‐Conjugated Organic Materials at the Polymer Limit: Experiment and Theory , 2007 .

[19]  A. Klamt,et al.  COSMO : a new approach to dielectric screening in solvents with explicit expressions for the screening energy and its gradient , 1993 .

[20]  Jörg Rissler,et al.  Effective conjugation length of π-conjugated systems , 2004 .

[21]  David J. Tozer,et al.  Relationship between long-range charge-transfer excitation energy error and integer discontinuity in Kohn–Sham theory , 2003 .

[22]  Gunter,et al.  Monodisperse poly(triacetylene) oligomers extending from monomer to hexadecamer: joint experimental and theoretical investigation of physical properties , 2000, Chemistry.

[23]  A R Bishop,et al.  Conformational dynamics of photoexcited conjugated molecules. , 2002, Physical review letters.

[24]  K. Hirao,et al.  A long-range correction scheme for generalized-gradient-approximation exchange functionals , 2001 .

[25]  U. Stalmach,et al.  Effective conjugation length and UV/vis spectra of oligomers , 1997 .

[26]  S. Tretiak,et al.  Dependence of Spurious Charge-Transfer Excited States on Orbital Exchange in TDDFT:  Large Molecules and Clusters. , 2007, Journal of chemical theory and computation.

[27]  R. Baer,et al.  Prediction of charge-transfer excitations in coumarin-based dyes using a range-separated functional tuned from first principles. , 2009, The Journal of chemical physics.

[28]  M. Frisch,et al.  Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields , 1994 .

[29]  M. Head‐Gordon,et al.  Failure of time-dependent density functional theory for long-range charge-transfer excited states: the zincbacteriochlorin-bacteriochlorin and bacteriochlorophyll-spheroidene complexes. , 2004, Journal of the American Chemical Society.

[30]  M. Head‐Gordon,et al.  Systematic optimization of long-range corrected hybrid density functionals. , 2008, The Journal of chemical physics.

[31]  R. Baer,et al.  Reliable prediction of charge transfer excitations in molecular complexes using time-dependent density functional theory. , 2009, Journal of the American Chemical Society.

[32]  Kimihiko Hirao,et al.  Polarizability and second hyperpolarizability evaluation of long molecules by the density functional theory with long-range correction. , 2007, The Journal of chemical physics.