Baz wrote:
I am no expert but,
If you mean Photosynthesis, that process has ended because the fruits have
grown, the pollination has ceased because of defoliation and no more
trusses will appear. The little tiny tomatoes and flower should be taken
off, they will serve no purpose now, in fact they should have been nipped
weeks ago.

If my understanding is correct, the tomato ripens to a red colour so that
the birds are attracted to it for food. The birds eat the sugary bits of
the tomato and also some seed.
The bird then flies away to have a poo and places a seed in situ. The seed
grows into a plant when the temperature allows, usually in spring.

By defoliation what you are doing is fooling the tomato plant into thinking
it is autumn and "it's time I started to ripen my fruit into a nice red
colour" to attract the birds in order to disperse the s........and so on.

As I say I am no expert but the above is what I beleive happens.

You could well be right. But I'm puzzled about where the energy to convert
from green to red comes from, given it's not using photosynthesis, and that
is the main (afaik!) source of energy.

I also don't really see why you need to put energy into ripening just yet,
it's not as if the days are getting seriously short yet. By mid October I
may well agree, but for now I'm still happy for, at least my cherries, to
still attempt to turn flowers into fruits.