Symmetric, symmetrical, unsymmetric... Need some help!

[tocket]

I'm having some difficulties related to the English language here. You see, my thesis which I'm just about to present is currently titled "Symmetric and unsymmetric donor functionalization of chromophores for dye sensitized solar cells" and I can't help it but to wonder if this is correct. What's the correct adjective for symmetry? Is an object symmetric or symmetrical? Unsymmetric or unsymmetrical? MS Word seems to think unsymmetric is not a word, but on the other hand it thinks the same of functionalization which is in fact a word.

Not being a native english speaker myself I would really appreaciate some input on this subject. Getting the title of my thesis wrong would be embarrassing!

Here are some examples of how I use the term:

1. The series consists of three symmetric and one unsymmetric dye. One of the symmetric dyes showed a remarkably high VOC and the best performance in DSCs with a light to electricity conversion efficiency of 6% under AM 1.5G conditions.
2. During the course of the project the possibility of introducing two different donor groups opened up; resulting in the unsymmetrical dye D37.
3. However, the peak for the unsymmetrical dye is slightly broadened compared to that of the symmetrical dyes.
4. Interestingly, the unsymmetrical dye does not show this high extinction coefficient; it is in fact even lower than D5.
5. Quantum chemical methods indicate distinct advantages arising from the introduction of two different donor groups, i.e. making an unsymmetrical dye.

[heroic]

"Asymmetrical".

-J.

[tocket]

Unfortunately asymmetrical has a special meaning in chemistry. It implies chirality. My dyes are neither chiral nor symmetric.

http://en.wikipedia.org/wiki/Chirality_(chemistry)

[Agent C]

If you have SciFinder do a quick literature search to see what other people have titled their papers.

[Pitts]

What about nonsymmetrical..
see
www.britannica.com/EBchecked/topic/417858/nonsymmetrical-relation - 49k -

I'm no expert though.

Cheers
Ray
NZ

[drlava]

yeah non-symmetric might work

[The_Doctor]

This runs deeper than syntax or semantics. It might be possible to avoid the word 'symmetry', or at least possible to apply it very specifically to avoid conflict of meanings. If the dyes do not differ in chirality, in what way are they not symmetrical? Arrangements of bound atoms other than chiral, so some sort of molecular symmetry? (I don't know chemistry well enough to give an example, but I think there'd be some, and I can't find any diagrams of D37 dye, all detailed references Google provides seem to be closed to the public).

Anyway, it might be possible to evade confusion by using terms 'mono-symmetrical' and 'bi-symmetrical' and such. Or more likely better to apply the term to the attribute of the dye molecule to distinguish explicitly from notions of chirality.

[tocket]

If you have SciFinder do a quick literature search to see what other people have titled their papers.

That's not a bad idea! It seems unsymmetrical gets a lot more hits than unsymmetric, and narrowing the search down a bit it seems that unsymmetrical is the form that should be used.

What about nonsymmetrical..
see
www.britannica.com/EBchecked/topic/417858/nonsymmetrical-relation - 49k -

I'm no expert though.

Cheers
Ray
NZ

I prefer unsymmetric/unsymmetrical really, I've never seen any mention of non-symmetrical in chemistry contexts.

This runs deeper than syntax or semantics. It might be possible to avoid the word 'symmetry', or at least possible to apply it very specifically to avoid conflict of meanings. If the dyes do not differ in chirality, in what way are they not symmetrical? Arrangements of bound atoms other than chiral, so some sort of molecular symmetry? (I don't know chemistry well enough to give an example, but I think there'd be some, and I can't find any diagrams of D37 dye, all detailed references Google provides seem to be closed to the public).

Anyway, it might be possible to evade confusion by using terms 'mono-symmetrical' and 'bi-symmetrical' and such. Or more likely better to apply the term to the attribute of the dye molecule to distinguish explicitly from notions of chirality.

Perhaps I should present what kind of "unsymmetry" I'm talking about. The dyes I'm working on are based around a nitrogen, which is bonded to 3 groups. It can be considered planar, so 2 dimensional symmetry is sufficient. If they are all the same that would be a highly symmetrical molecule (cyclic symmetry group). Normally the dyes have two different groups though, two "donors" and one "acceptor". The donor groups are the same though, this means that if you somehow chop the molecule in half along the acceptor bond you will end up with two identical halves and putting one of them on a mirror would make it look though as if you had the whole molecule. What I've done in the unsymmetrical dye is to have two different donor groups, effectively removing this symmetry element. The molecule still exhibits some symmetry though, because it's planar.

Looking at the picture below, symmetric donor functionalization is when R1 = A and R2 = R3 = D, whereas in the unsymmetrical case R1 = A, R2 = D and R3 = D'.

[The_Doctor]

That Wikipedia article on chemical chirality says, about 15 lines in: "A chiral molecule is not necessarily asymmetric, that is, devoid of any symmetry elements, as it can have, for example, rotational symmetry".

The maths article on chirality is clearer, saying a shape is chiral "...if it cannot be mapped to its mirror image by rotations and translations alone." The inverse of chiral is achiral, or maybe non-chiral.

Going with convention is a good way to avoid embarrassment, but what if the convention itself was lazy? You won't look bad if you evade a weak convention. Given that internal symmetry cannot be entirely mapped if the molecule can be considered planar, because Z axis symmetry is ignored, chirality isn't an issue.

I think 'asymmetrical' is fine. Chirality has its own specific terms. If you need to clarify, maybe do it early in the 'abstract' or other introductory stuff.


EDIT: I noticed the words 'solar cells'. Is this to do with using dyes to absorb shortwave light, then re-emit on lower wavelengths to increase yield in silicon's electrical output? I really like that idea, so if you're working on that, all power to you. I especially like the idea of using total internal reflection to duct light from the bulk of a plate to the edge, to minimise the amount of expensive silicon cell needed. I don't know how much progress there is on this, I just watch and wait the way gamers watch for a new CPU or graphics card..

[tocket]

While chiral molecules are not necessarily chiral, the two are often used synonymously. An example can be found here http://en.wikipedia.org/wiki/Asymmetric_synthesis.

I suspect a lot of people at the department would be confused if I used the term asymmetrical with something that is not chiral. You're right though, I should probably add a few lines on the choice of terminology.

Regarding the actual solar cells, the dye is used to enable the absorption of visible light by "untypical" semiconductors. There's no silicon in the cell. The focus is currently on titanium dioxide, which is far cheaper than the high purity silicon used in current solar cells. In fact, you probably have your walls coated with titanium dioxide if the room is painted white. Unmodified titania will only absorb UV, but if you put a dye on it, the dye will start kicking excited electrons into the titania, creating a current. The point of all this? Well, how does cheap, printable and environmentally friendly solar cells sound? Of course, there are some problems that need to be ironed out first...