Finally getting the artificial/hypothetical part is what you actually asked for I dug deeper into this.
There is research on Artificial Photosynthesis dealing with what potential substances could be used to create a photosystem.
The photosensitizers commonly used in artificial photosynthesis are mainly metal-containing complexes including platinum, rhodium, iridium and most often ruthenium as ruthenium polypyridine complexes.
Organic complexes successfully used as photosensitizers are eosin Y and rose bengal.
The part of the photosystem determining what wavelengths can be used for photosynthesis is the Light-harvesting complex.
And now to answer your original question
Are there any other hypothetical chemical compounds which can transform energy from other portions of the spectrum?
Yes there are. A lot.
Absorption of a photon by a molecule can lead to electronic excitation when the energy of the captured photon matches that of an electronic transition.
So basically, any molecule capable of absorbing photons / electromagnetic radiation – be it visible light or something else – could be used to harvest light / radiation.
Natural Photosynthesis in plants
plus other accessory pigments / carotenoids
Just to add some accessory pigments for reference:
Name | absorption maximum
- Chlorophyll c | 500-600nm
- Chlorophyll d | 710nm
- Chlorophyll f | 720nm
Natural Photosynthesis in other organisms
As has been mentioned in the comments there is also bacteriochlorophyll which is found in purple bacteria.
Name | absorption maxima
- Bacteriochlorophyll a | 805, 830-890
- Bacteriochlorophyll b | 835-850, 1020-1040
- Bacteriochlorophyll c | 745-755
- Bacteriochlorophyll cs| 740
- Bacteriochlorophyll d | 705-740
- Bacteriochlorophyll e | 719-726
- Bacteriochlorophyll f | 700-710
- Bacteriochlorophyll g | 670, 788
Cyanobacteria, red algae and glaucophytes
The phycobilisomes found in these organisms can harvest light between 500 and 650nm depending on their structure.
And to give you an idea of what scientist think is possible in terms of naturally occurring photosynthesis / photosynthetic pigments on earth checkout http://sydney.edu.au/news/84.html?newsstoryid=5463.
Quote from the article:
"Discovering this new chlorophyll has completely overturned the traditional notion that photosynthesis needs high energy light," Dr Chen said.
"It is amazing that this new molecule, with a simple change to its chemical structure, can absorb extremely low energy light. This means that photosynthetic organisms can utilize a much larger portion of the solar spectrum than we previously thought and that the efficiency of photosynthesis is much greater than we ever imagined.