Obituary Prof. Dr. Gerd Heppke

Figures & data

Figure 1. Prof. Gerd Heppke 1991 (Foto: Inge Kundel-Saro).

Table 1. Examples of various mesophases and their physical properties studied by Gerd Heppke, his students, and scientists collaborating with him. (N nematic; BP blue phase; Sm smectic; TGB twist grain boundary phase; Col columnar; P pyramidal; an asterix ‘*’ indicates the respective chiral modification, suffixes mean: ‘1’ monolayer, ‘d’ partial bilayer, ‘2’ bilayer, ‘s’ synclinic, ‘a’ anticlinic, ‘F’ ferroelectric, and ‘A’ antiferroelectric smectic ordering; the suffix ‘D’ indicates a respective phase composed of disc-like molecules; B₂, B₃, B₄ and B₇ are traditional abbreviations for mesophases composed of bent-core molecules). The electro-optic effects include (i) scattering → transparent transitions, (ii) reorientation of the optical axis, (iii) dichroism, (iv) colour changes, (v) Kerr effect, (vi) field-induced phase transitions, or (-) no switching observed in a higher ordered chiral smectic phase.

Class of compounds	Meso-phase	Polymorphism, phase diagram and/or phase structure	Helical pitch and/or selective reflection	Electric conductivity, dielectric permittivity and/or spontaneous polarisation	Electro-optic effects	Dynamic behaviour (e.g. viscosity and/or switching speed)	Optical nonlinearity including second harmonic generation(SHG)	Vitrified, glass-like state
Thermotropic: calamitic	N	[1,5–8,11]	-	[3,4]	[4] (i), [10] (iii)	[2]
	N*		[12,13,19–21,32]		[9] (vi)
	Blue Phases BPI- III, BPH		[14–17]		[14] (iv, vi), [15–17] (iv), [18] (v)			[72]
	TGB	[45,47]
	SmA1, SmAd, SmA2	[5–8,78]
	SmC1, SmCd, SmC2	[79]
	SmCa	[38]
	SmO (=SmCa)	[38]
	SmA*	[22,26,27,39,40]		[24]	[28,33] (ii), [24,29,30] (vi)			[73]
	De Vries SmA*	[48]
	SmB*				[33] (ii)
	SmC*	[22–27,40,42]	[32,35,46]	[22,23,31,35,40,42,47]	[22,23,31,42,44,47] (ii)	[22,23,35,[42]]	[74]	[73,74]
	SmCα*	[40,45–47]		[40]	[44] (ii)
	SmCβ*	[46]
	SmCβ*	[40,45–47]		[40]	[44] (ii)
	SmCA*	[38–40,42,45,46]	[46]	[40–42,46,47]	[40,42,44] (ii)	[41,42]
	SmE*	[33]			[33] (ii)
	SmF*	[36]
	SmG*	[30,36]			[36] (-)
	SmH*	[36]			[36] (-)
	SmI*	[36,40]
	SmIA*	[40,42,46]		[40,42]	[42] (ii)
	SmJ*	[36,34,37]		[36]	[36] (ii)
	SmM* or SmM’*	[34–37]	[35]	[35–37]	[37] (ii)	[35]
	SmO* (=SmCa*)	[38]
	SmQ*	[39,43,[45]]
Thermotropic: discotic	ND							[75]
	N D*	[49–51]	[49–51]		[51] (iv)			[49]
	BPDI, BPDII, BPDIII	[49,54,76]	[54]					[49,76]
	Col*	[52,54]		[52,54]	[52,54] (ii)	[52–54]
Thermotropic: pyramidal molecules	P	[55]				[55]
Thermotropic: bent-shaped molecules	B2: SmCsPF, SmCsPA, SmCaPF, SmCaPA	[56–60,63]		[58,77]	[58] (ii) [61,77] (i)	[58,61,[63],77]	[64–67,77]	[77]
	B3	[58,60]
	B4: HNF	[60,69]					[66,67]	[69]
	B7: SmCG*	[59,60,62]		[59,60]	[60] (ii),
	M1: SmCG*	[63]		[63]	[63] (ii)	[63]
Lyotropic: discotic molecules in dodecane	NCol*	[70]	[70]		[70] (ii)			[71]
	TGBCol ?	[70]
	Col* (‘D1’),Col* (‘D2’)	[70]			[70] (ii)

Figure 2. Examples of experimental results and insights. (a) Modified Grandjano-Cano preparation facilitating to determine the handedness of a chiral nematic helical structure (reproduced from Ref [13]. with kind permission by Taylor & Francis). (b) Electric field-induced colour change of the selective reflection of blue phase I (left) and blue phase II (right) as described in Ref [14]. (c) Phase transition observed by polarising optical microscopy in a compound exhibiting the higher ordered smectic SmQ* phase as described in Refs. [39,43]. (d) Surface topography of a discotic blue phase measured by atomic force microscopy (reproduced from Ref [76]. with kind permission by the Royal Society of Chemistry). (e) Sketch explaining how achiral bent-core molecules may form a tilted smectic phase that is chiral, i. e. not identical to its mirror image (reproduced from Ref [56]. with kind permission by the American Association for the Advancement of Science. (f) Intensity of the second harmonic generation (SHG) signal indicating a field-induced transition from an achiral to a chiral state in a mesophase composed of achiral bent-core molecules (reproduced from Ref [65]. with kind permission by the American Physical Society).

Figure 3. Examples of books, professional meetings and outreach activities by Prof. Gerd Heppke. (a) Cover of a book [90] published on the occasion of the Liquid Crystal Meeting 1980 at Garmisch-Partenkirchen (Germany). (b) Gerd Heppke and Gerhard Meier (Fraunhofer IAF Freiburg) at the Bunsen-Colloquium 1983, which was organised by Heppke in Berlin. (c) Exhibition at the Hannover Fair 1985, where general properties of liquid crystals, the selective reflection of blue phases, and an optical transmission line of acoustic signals utilising an electro-optic modulator were demonstrated.

Heppke G, Schneider F. ESR-spektroskopische Untersuchungen des Ordnungsgrades von Vanadylacetylacetonat in kristallin-flüssigem und glasig erstarrtem N-(p-Methoxybenzyliden)-p-n-butylanilin. Ber Bunsenges Phys Chem. 1971;75(1):61–65.

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Heppke G, Martens J, Praefcke K, et al. Organic selenium-compounds. 3. Selenol esters – novel class of liquid crystal compounds. Angew Chem Int Ed. 1977;16(5):318–319.

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Heppke G, Schneider F. Untersuchungen der elektrischen Leitfähigkeit homologer 4,4′-Di-n-alkyloxy-azoxybenzole im nematischen Phasenbereich. Z Naturforsch A Phys Sci. 1975;30a:316–322.

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Bock M, Heppke G, Richter E-J, et al. Electric conductivity of liquid crystal mixtures with induced smectic phases. Mol Cryst Liq Cryst. 1978;45:221–229.

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Heppke G, Knippenberg B, Möller A, et al. Colored and black liquid crystalline mixtures with new antraquinone dyes. Mol Cryst Liq Cryst. 1983;94:1–2, 191–204.

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Heppke G, Schneider F. Kinetics of aligsnment of a nematic liquid crystal in magnetic fields – a method for measuring the rotational viscosity γ1. Z Naturforsch A. 1973;27(6):976–982.

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Heppke G, Oestreicher F. Determination of helical sense of cholesteric liquid crystals using Grandjean-Cano method. Z Naturforsch A. 1977;32(8):899–901.

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Heppke G, Oestreicher F. Determination of cholesteric screw sense. Mol Cryst Liq Cryst. 1978;41(9):245–249.

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Bahr C, Escher C, Fliegner D, et al. Behaviour of helical pitch in cholesteric and chiral smectic C* phases. Ber Bunsenges Phys Chem. 1991;95(10):1233–1237.

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Göbl-Wunsch A, Heppke G, Oestreicher F. Temperature independent threshold voltage for an electrooptic effect. J Phys (Paris). 1979;40(8):773–777.

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Heppke G, Krumrey M, Oestreicher F. Observation of electro-optical effects in blue phase systems. Mol Cryst Liq Cryst. 1983;99(1–4):99–105.

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Heppke G, Kitzerow HS, Krumrey M. Electric-field induced variation of the refractive index in cholesteric blue phases. Mol Cryst Liq Cryst Lett. 1985;2(1–2):59–65.

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Kitzerow HS, Schmid H, Ranft A, et al. Observation of blue phases in chiral networks. Liq Cryst. 1993;14(3):911–916.

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Lagerwall JPF, Giesselmann F, Selbmann C, et al. Generation of frustrated liquid crystal phases by mixing an achiral nematic–smectic-C mesogen with an antiferroelectric chiral smectic liquid crystal. J Chem Phys. 2005;122:144906.

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Goc F, Selbmann C, Rauch S, et al. Induction of antiferroelectric phases in high tilt chiral smectics by doping with bent-shaped liquid crystals. Mol Cryst Liq Cryst. 2005;439:147–160.

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Shashidar R, Ratna BR, Prasad SK, et al. Smectic-Ad-smectic-A2 critical point. Phys Rev Lett. 1987;59(11):1209–1211.

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Wen X, Garland CW, Heppke G. Calorimetric investigation of nematic —smectic-A2 and smectic-A2 —smectic-C2 transitions. Phys Rev A. 1991;44(8):5064–5068.

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Heppke G, Kleineberg P, Lötzsch D. Synthesis and liquid crystalline propertiesbof a homologous series of antiferroelectric liquid crystals and their respective racemates. Liq Cryst. 1993;14(1):67–71.

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Bahr C, Heppke G. Ferroelectric liquid crystals with high spontaneous polarization. Mol Cryst Liq Cryst. 1986;4(2):31–37. Part: Letter.

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Ratna BR, Shashidar R, Nair GG, et al. Evidence of a 1st order smectic-A smectic-C-star transition and its approach to tricritical behavior. Phys Rev A. 1988;37(5):1824–1826.

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Liu HY, Huang CC, Bahr C, et al. Tricriticality near the smectic-A-smectic-C transition of a liquid crystal compound. Phys Rev Lett 1988;61(3):345–348. doi:10.1103/PhysRevLett.61.345.

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Bennemann D, Heppke G, Levelut AM, et al. X-ray miscibility investigations on new compounds exhibiting wide range smectic Q phases. Mol Cryst Liq Cryst. 1995;260:351–360.

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Mery S, Lötzsch D, Heppke G, et al. Antiferroelectric and ferrielectric liquid crystalline low molar mass materials and polymers. Liq Cryst. 1997;23(5):629–644.

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Bahr C, Heppke G, Sharma NK. Dielectric studies of the smectic-C-smectic-A transition of a ferroelectric liquid crystal with high spontaneous polarization. Ferroelectrics. 1987;76(1–2):151–157.

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Bahr C, Heppke G. Optical and dielectric investigations on the electroclinic effect exhibited by a ferroelectric liquid crystal with high spontaneous polarization. Liq Cryst. 1987;2(6):825–831.

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Bahr C, Heppke G. Electroclinic effect in smectic-B and -E phases of chiral molecules. Phys Rev A. 1988;37(8):3179–3181.

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Bahr C, Heppke G. Electric-field induced smectic A to smectic-C transition in ferroelectric liquid crystals. Mol Cryst Liq Cryst. 1987;150B:313–324.

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Bahr C, Heppke G. Influence of electric field on a 1st order smectic A ferroelectric smectic C liquid crystal phase transition – a field-induced critical point. Phys Rev A. 1990;41(8):4335–4342.

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Bömelburg J, Heppke G, Wuthe K. Glass forming low-molecular mass ferroelectric liquid crystals. Proc SPIE. 1994;2175:10–20.

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Hayashi N, Kocot A, Linehan MJ, et al. Experimental demonstration, using polarized Raman and infrared spectroscopy, that both conventional and de Vries smectic-A phases may exist in smectic liquid crystals with a first-order A−C* transition. Phys Rev E. 2006;74(5):051706.

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Heppke G, Lötzsch D, Morr M, et al. New chiral side chains for ferro- and antiferro-electric liquid crystals derived from the preen-gland wax of the domestic goose. J Mater Chem. 1997;7(10):1993–1999.

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Bahr C, Heppke G, Wuthe K. Dielectric, viscosity, and pitch measurements of a ferroelectric liquid crystal exhibiting the phase sequence smectic M-smectic C. Liq Cryst. 1992;12(6):997–1003.

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Lagerwall JPF, Heppke G, Giesselmann F. Frustration between syn- and anticlinicity in mixtures of chiral and non-chiral tilted smectic-C–type liquid crystals. Eur Phys J E. 2005;18:113–121.

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Bahr C, Heppke G. Ferroelectric liquid crystals – properties of binary mixtures and pure compounds with high spontaneous polarization. Mol Cryst Liq Cryst. 1987;148:29–43.

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Bömelburg J, Hänsel C, Heppke G, et al. Mesogenic compounds with two Chiral Lateral Groups: new chiral dopants for ferroelectric liquid crystals. Mol Cryst Liq Cryst. 1990;192(1):335–343.

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Skarabot M, Cepic M, Zeks B, et al. Birefringence and tilt angle in the antiferroelectric, ferroelectric, and intermediate phases of chiral smectic liquid crystals. Phys Rev E. 1998;58(1):575–584.

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Loddoch M, Marowsky G, Schmid H, et al. Novel glass-forming ferroelectric liquid crystal material of high second-order nonlinearity. Appl Phys B. 1994;59:591–595.

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Buivydas M, Gouda F, Andersson G, et al. Collective and non-collective excitations in antiferroelectric and ferrielectric liquid crystals studied by dielectric relaxation spectroscopy and electro-optic measurements. Liq Cryst. 1997;23(5):723–739.

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Heppke G, Lötzsch D, Sharma NK, et al. Liquid crystalline 2-[4-(2-chloroalkanoyloxy)-phenyl −5-(4-n-hexyloxyphenyl)-pyrimidines–new ferroelectric compounds exhibiting interesting polymorphism. Mol Cryst Liq Cryst. 1994;241(1):275–288.

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Heppke G, Lötzsch D, Demus D, et al. The SmM phase: evidence for a new type of tilted smectic phase. Mol Cryst Liq Cryst. 1991;208(1):9–19.

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Heppke G, Lötzsch D, Kampa B, et al. Synthese und ferroelektrische Eigenschaften einer homologen Serie chiraler 2,5-Diphenylpyrimidine. Journal für Praktische Chemie/Chemiker-Zeitung. 1993;335(6):549–554.

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Levelut AM, Hallouin E, Bennemann D, et al. The smectic Q phase, a crystal of twist grain boundaries with smectic order. J Phys France II. 1997;7(7):981–1000.

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Contzen J, Heppke G, Kitzerow HS, et al. Storage of laser-induced holographic gratings in discotic liquid crystals. Appl Phys B. 1996;63:606–608.

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Krüerke D, Gough N, Heppke G, et al. Electrically tuneable cholesteric mirror. Mol Cryst Liq Cryst. 2000;351(1):69–78.

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Krüerke D, Kitzerow HS, Heppke G, et al. First observation of selective reflection and blue phases in chiral discotic liquid crystals. Ber Bunsenges Phys Chem. 1993;97(10):1371–1375.

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Heppke G, Krüerke D, Löhning C, et al. New chiral discotic triphenylene derivatives exhibiting a cholesteric blue phase and a ferroelectrically switchable columnar mesophase. J Mater Chem. 2000;10(12):2657–2661.

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Hauser A, Thieme M, Saupe A, et al. Surface-imaging of frozen blue phases in a discotic liquid crystal with atomic force microscopy. J Mater Chem. 1997;7(11):2223–2229.

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Heppke G, Krüerke D, Müller M, et al. Investigations on electrooptical effects in chiral discotic columnar mesophases. Ferroelectrics. 1996;179:203–209.

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Jákli A, Müller M, Heppke G. Rheology of a pyramidal liquid crystal. Liq Cryst. 1999;26(7):945–952.

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Rauch S, Bault P, Sawade H, et al. Ferroelectric-chiral-antiferroelectric-racemic liquid crystal phase transition of bent-shape molecules. Phys Rev E. 2002;66(2):021706. Part: 1.

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Heppke G, Jakli A, Rauch S, et al. Electric-field-induced chiral separation in-liquid crystals. Phys Rev E. 1999;60(5):5575–5579. Part: A.

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Rauch S, Selbmann C, Bault P, et al. Glass forming banana-shaped compounds: vitrified liquid crystal states. Phys Rev E. 2004;69(2):021707. Part: 1.

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Jakli A, Chien LC, Krüerke D, et al. Light shutters from antiferroelectric liquid crystals of bent-shaped molecules. Liq Cryst. 2002;29(3):377–381.

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Heppke G, Parghi DD, Sawade H. Novel sulphur-containing banana-shaped liquid crystal molecules. Liq Cryst. 2000;27(3):313–320.

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Hough LE, Jung HT, Krüerke D, et al. Helical nanofilament phases. Science. 2009;325(5939):456–460.

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Morales-Saavedra OG, Jákli A, Heppke G, et al. Polar micro structures of the B2 and B4 phases of bent-shaped LC-molecules resolved by nonlinear optical microscopy. J Nonlinear Opt Phys Mater. 2006;15(2):287–302.

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Morales-Saavedra OG, Jákli A, Heppke G, et al. Polar ordering in thermotropic mesogens resolved by scanning NLO microscopy. J Nonlinear Opt Phys Mater. 2006;15(4):431–446.

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Heppke G, Parghi DD, Sawade H. A laterally fluoro-substituted “banana-shaped” liquid crystal showing antiferroelectricity. Ferroelectrics. 2000;243(1–4):269–276.

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Jakli A, Krüerke D, Sawade H, et al. Evidence for triclinic symmetry in smectic liquid crystals of bent-shape molecules. Phys Rev Lett. 2001;86(25):5715–5718.

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Krüerke D, Rudquist P, Lagerwall ST, et al. Ferroelectric switching of chiral discotic lyomesophases. Ferroelectrics. 2000;243:207–220.

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Olenik ID, Spindler L, Copic M, et al. Glasslike character of molecular ordering in discotic lyomesophyses. Phys Rev E. 2001;65:011705.

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Heppke G, Moro D. Liquid crystals - Chiral order from achiral molecules. Science. 1998;279(5358):1872–1873.

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Macdonald R, Kentischer F, Warnick P, et al. Antiferroelectricity and chiral order in new liquid crystals of nonchiral molecules studied by optical second harmonic generation. Phys Rev Lett. 1998;81(20):4408–4411.

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Liquid crystals of one- and two-dimensional order. In: Helfrich W, Heppke G, Editors. Proceedings of the Conference on Liquid Crystals of One- and Two-Dimensional Order and Their Applications, Garmisch- Partenkirchen (Germany, January 21–25, 1980). Springer Series in Chemical Physics, Vol 11, Springer-Verlag, Berlin, Heidelberg New York; 1980.

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