Organic & Hybrid Photonic Crystals

Photonic crystals (PhC) are composite systems where materials possessing different refractive index are arranged in a highly regular periodical structure having a length scale comparable to the wavelength of visible light[1]. The periodicity of the system can be extended over 1-, 2- or 3-dimensions. The concept of PhC have been disclosed about twenty-five years ago by Yablonovitch[2] and John[3] with two seminal papers tackling fundamental issues like inhibition of spontaneous emission and light localization. Nowadays, PhCs find application in different fields spanning from photonics to photovoltaics and are gaining a great interest for sensing.[4-9] While the most widespread techniques used to growth photonic crystals are top-down ones, a great interest is currently devoted to fabrication of novel PhC structures with bottom-up methods or by processing from solution/melt. Moreover, their functionalization with suitable groups and/or with photoactive organic/hybrid materials in order to tailor their responsive properties for selected applications is intensively pursued.[4-5, 9-11] In this communication, we will review the opportunities provided by organic PhC and we will focus on recent results obtained with 2D and 3D colloidal arrays (respectively, microsphere monolayers and opals) as well as on 1D all-polymer structures, which may add to photonic functionality unprecedented properties for their inorganic counterpart such as self-support (no need for a substrate) and mechanical flexibility. 1D all-polymer photonic crystals (i.e. Distributed Bragg Reflectors and microcavities) are grown by spin-coating by using polymer solutions in orthogonal solvents.[12-13] Even though, the technique is very simple, cheap and well known, limitations occurs when different constraints, such as high dielectric contrast, orthogonal solvents, control of the interfaces, transparency, lack of light scattering, have to be simultaneously considered. In spite of that, the technique allows to prepare free-standing and flexible DBR and microcavities, which can be successfully doped with photoactive materials (semiconducting, photochromic and clathrating polymers, J-aggregates) in order to obtain photonic platforms suitable for lasing, switching and sensing[12-14]. 2D PhC, i.e. microsphere arrays can be prepared by floating[15]. Such systems have been successfully used as a template for grazing incident gold evaporation thus generating nanocrescents possessing different kind of anisotropic plasmonic resonances[15], which interact with photonic modes in opals. Moreover, microsphere monolayers show unusual second harmonic generation of circular dichroism[16]. Finally, artificial opals, the well-known playground for 3D photonic crystals have been used to show fluorescence enhancement effects and modulation of the radiative fluorescence lifetime. Three examples are described such as opals infiltrated with fluorescent solutions, opal infiltrated with conjugated polymers, and core-shell opals where the microspheres have been engineered in order to possess a shell doped with a fluorophore[17-18]. References [1] J. D. Joannopulos; R. D. Meade; J. N. Win, Photonic Crystals: Molding the Flow of the Light. Princeton University Press: Princeton, 1995. [2] E. Yablonovitch, Phys. Rev. Lett. 1987, 58. [3] S. John, Phys. Rev. Lett. 1987, 58. [4] J. Ge; Y. Yin, Angew. Chem. Int. Ed. 2011, 50, 1492. [5] F. Li; D. P. Josephson; A. Stein, Angew. Chem. Int. Ed. 2011, 50, 360. [6] T. Asano; S. Noda, Nature 2004, 429, 6988. [7] D. Graham-Rowe, Nat Photon 2009, 3. [8] M. F. Limonov; R. M. D. L. Rue, Optical Properties of Photonic Structures: Interplay of Order and Disorder. Taylor & Francis: 2012. [9] J.-H. Lee; C. Y. Koh; J. P. Singer; S.-J. Jeon; M. Maldovan; O. Stein; E. L. Thomas, Adv. Mater. 2013, 26, 532. [10] J. H. Moon; S. Yang, Chemical Reviews 2009, 110, 547. [11] S. Furumi; H. Fudouzi; H. T. Miyazaki; Y. Sakka, Adv. Mater. 2007, 19. [12] L. Frezza; M. Patrini; M. Liscidini; D. Comoretto, J. Phys. Chem. C 2011, 115, 19939. [13] G. Canazza; F. Scotognella; G. Lanzani; S. D. Silvestri; M. Zavelani-Rossi; D. Comoretto, Laser Phys. Lett. in press (2014). [14] S. Pirotta; M. Patrini; M. Liscidini; M. Galli; G. Dacarro; G. Canazza; G. Guizzetti; D. Comoretto; D. Bajoni, Appl. Phys. Lett. 2014, 104. [15] V. Robbiano; M. Giordano; C. Martella; F. D. Stasio; D. Chiappe; F. B. d. Mongeot; D. Comoretto, Adv. Optical Mater. 2013, 1, 389. [16] A. Belardini; A. Benedetti; M. Centini; G. Leahu; F. Mura; S. Sennato; C. Sibilia; V. Robbiano; M. C. Giordano; C. Martella; D. Comoretto; F. Buatier de Mongeot, Adv. Optical Mater. DOI: 10.1002/adom.201300385. [17] L. Berti; M. Cucini; F. Di Stasio; D. Comoretto; M. Galli; F. Marabelli; N. Manfredi; C. Marinzi; A. Abbotto, J. Phys. Chem. C 2010, 114, 2403. [18] F. Di Stasio; L. Berti; S. O. McDonnell; V. Robbiano; H. L. Anderson; D. Comoretto; F. Cacialli, APL Materials 2013, 1