The Limited Palette for Photonic Block‐Copolymer Materials: A Historical Problem or a Practical Limitation?

Abstract Block‐copolymer self‐assembly has proven to be an effective route for the fabrication of photonic films and, more recently, photonic pigments. However, despite extensive research on this topic over the past two decades, the palette of monomers and polymers employed to produce such structurally colored materials has remained surprisingly limited. In this Scientific Perspective, the commonly used block‐copolymer systems reported in the literature are summarized (considering both linear and brush architectures) and their use is rationalized from the point of view of both their historical development and physicochemical constraints. Finally, the current challenges facing the field are discussed and promising new areas of research are highlighted to inspire the community to pursue new directions.

Section S3.Statistics of linear and brush block copolymers employed for photonic multilayer films or photonic particles (pigments).
Clarification of the fields used to classify block copolymers used for photonic materials: a Name: The linear block copolymers are named according to the convention: (first block)-b-(second block).The abbreviations are defined in Table S1.The brush block copolymers were named according to the rule: P(backbone-side chain 1)-b-P(backbone-side chain 2).The abbreviations are defined in Table S2.Additionally, the refractive indices of the blocks are given in parenthesis in the form: (Refractive index of block#1-Refractive index of block#2).All LBCPs are synthesized by anionic polymerization unless explicitly stated.Similarly, all BBCPs are prepared via ROMP of MMs unless explicitly stated otherwise.
b Mn (kDa) : The number average molecular weight (Mn) was taken directly from the articles where available.If unavailable, they were calculated from other parameters presented, for example, weight average molecular weight (Mw) and polydispersity index (PDI)."N/A" indicates that the Mn could not be obtained.For brush block copolymers, this also includes molecular weights (Mn) of the side chains (SC1 and SC2).
c PDI: The polydispersity index (PDI) was taken directly from the articles where available.If unavailable, they were calculated from other parameters provided, for example, weight average molecular weight (Mw) and number average molecular weight (Mn)."N/A" indicates that the PDI could not be obtained.The PDI was rounded to two decimal places.
d DP1, DP2, and DP1/DP2: The degree of polymerization (DP) is provided for each block, (i.e., DP1 and DP2 for block#1 and block#2, respectively) and were either taken from the articles or, if not directly available, estimated from other parameters presented, for example, the ratio of the molecular weight of each block and that of the respective monomer."N/A" indicates that the DP could not be obtained.The ratio DP1/DP2 were calculated to one decimal place.
e Formation method: The method by which the lamellar structure was produced from the BCP.
f Tuning method: The method used to tune the characteristic wavelength, typically through altering the native domain spacing.The abbreviations are defined in Table S3.
A dash is used to show that several treatments were applied."N/A" indicates that the tuning methods were not reported in the article.
g Solvent: The preparation solvent from which the photonic BCP film was drop-cast.
The abbreviations are defined in Table S4."N/A" represents that no solvents have been used (i.e., the film was cast from a BCP melt) or the used solvents were not stated in the article.
h  (nm) or  (nm): The domain spacing  of the formed lamellar structure, defined as the total thickness of a layer comprised of one domain of block#1 and one domain of block#2 (i.e.,  =  1 +  2 , as defined in Figure 1a of this article).For photonic porous particles (as in Table S9), the center-to-center correlation distance, 2 , is stated as the photonic dimension."N/A" indicates that no specific domain spacing value was reported."Native" domain spacing indicates that the value was measured from a dry film in the absence of any further treatment, such as solvent swelling.As different methods were used to measure and evaluate domain spacings, the value presented was chosen according to the following order of priority if more than one measurement technique was reported: XS (X-ray scattering), TEM (transmission electron microscopy), SEM (scanning electron microscopy), AFM (atomic force microscopy), NS (neutron scattering), other techniques.It should be noted that this order was chosen to simplify the information presented and does not necessarily comment on the relative accuracy of these techniques.In the case where more than one value was available using the same measurement method, both measurements will be exhibited (separated by a slash, /).If values were not given explicitly, they were extracted from the figures in the source article.The domain spacing is given to the nearest integer.
i   (nm): The characteristic wavelength  max is the wavelength at which the maximum intensity of light is reflected by the photonic structure.Conversely, when reflection spectra were not provided, this could also be determined from the position of the dip in the transmission spectrum."N/A" indicates that no such wavelength was reported."UV" indicates that the film reflected within the ultraviolet region and therefore appeared colorless."Native" represents that the value of the maximum characteristic wavelength was measured from a dry film without any further treatment, such as solvent swelling.As different methods were used to measure and evaluate the wavelength, the value presented was chosen according to the following order of priority if more than one measurement technique was available: reflection spectroscopy, transmission or absorption spectroscopy.It should be noted that this order was chosen to simplify the information presented and does not necessarily comment on the relative accuracy of the techniques.In the case where more than one value was available using the same measurement method, both measurements will be exhibited (separated by a slash, /).If values were not given explicitly, they were extracted from figures in the source article.The characteristic wavelength is given to the nearest integer. 1 [4] 266 N/A 1277 1265 1.0 CL-CI-SS N/A 421-747 CI-SS 510-586 1 [5] 265 1.07

Table S4 :
Common solvents used to cast BCP films, and their abbreviation.

Table S5 :
Linear block copolymers for photonic multilayer films.

Table S6 :
Linear block copolymers for photonic multilayer particles.

Table S7 :
Brush block copolymers for photonic multilayer films.

Table S8 :
Brush block copolymers for photonic multilayer particles.

Table S9 :
Brush block copolymers for photonic porous particles.