Clear-coats of polyurethanes may fit your profile - you would want to use aliphatic polyisocyanates to make sure you don't get discoloration by exposure to light (I'm assuming you're targeting a more flexible fiber optic for telecommunication).  I would think that resistance to IPA should be easy to get, and it is liquid before curing.  Depending on the polyurethane formulation, you would be able to get in between a hard glass and a soft elastomer easily.  Alternatively, you could go for an aliphatic epoxy, I think.  (Note: these are all my speculation, provided without any guarantee :) )

There are certain amine cured epoxies which are transparent like glass and are used for doming of labels on consumer goods. You may try some such epoxies, which are are available commercially.

Silicones can be made much more rigid than most people are aware. I have made them all the way from gels to 50 Shore D in durometer. Additionally, they have excellent optical stability over time. Contact Bluestar Silicones if you want more information. Maybe there is a readily available material to help you. If not, perhaps a custom formulation can be made if your volumes and the application needs can be matched. Otherwise, you could try the new ESA 7256 product (contact me for this, not quite commercial yet).

My proposal is to check if one of the following two opportunities fit:

a) synthesis of a special type of clear and transparent polyurethanes based on polyether polyols and trimerized aliphatic diisocyanates as described in WO 2010/ 108541. The polyurethanes produced may vary in a range of Shore 00 = 0 to Shore A = 90. Within this range a suitable formulation can be developed.

b) synthesis of poly(thiourethanes) from polythiols (SH-functionality 2 to 4, mw 200 to 4000) and cycloaliphatic diisocyanates or trimers as said above; the hardness may range from Shore A 30 to Shore D 90 depending on formulation

Any of the components are liquid at RT and have pot lifes after mixing of at least 3 min to 1 hour (in extreme cases longer times maybe established). The materials are UV stable and resistant to environmental effects (humidity, baceria etc.)

The hardness/flexibility of Silicone elastomers can be adjusted over an extremely wide range. They can be liquid in the uncured state and transparent as well. But the resistance against IPA (isopropyl alcohol) will remain an obstacle I would say.

Epoxy acrylates.. 

Silicones are the only polymer class with negligible NIR absorbtion. Therefore you need a harder type of silicone duromers. TEGO RC 722 from Evonik is a liquid silicone acrylate which can be easily cured with UV light using a photoinitiator like TEGO photoinitiator A18 which is a special type for such silicone acrylates. The hardness can be adjusted by adding a little amount of a high functional acrylate like pentaerytritol tetraacrylate but silicone must be the main component because of NIR absorbtion.

Look up Liquid Crystal Elastomers.