I am looking for a complete reference of UV/Vis spectroscopic data for organic materials ( mostly interested in λmax ) .
I have the CRC handbook but it only has data about some organic solvents in water and very limited data on dyes.
Can anyone suggest a comprehensive reference that includes the λmax of a wide variety of molecules in different solvents ?
To know the chemical name, molecular structure, or best: the unique registry number provided by the American Chemical Society (CAS-number) is beneficial in your search as trade names may vary depending on the supplier of the material you are interested in. The index number of the Colour Index (like C.I. 73000 for indigo) frequently used in the business of dyes potentially is of lesser use here. In decrease of data coverage:
There are commercial sources like Reaxys (by Elsevier) allowing to search for absorption data. As this (in part) emerged from a much senior database about chemical reactions, Beilstein (back to 1771) this is a typical database used in Departments of Chemistry at a University or Industry. SciFinder, based on the data indexed by the American Chemical Society equally allows you to find such data -- for both it might be helpful to request assistance / initial training to fully benefit from these sources.
Note: there is so much published data, none of both huge data bases may index / point back to all of the original journal articles, patents, conference proceedings, etc. pp. Depending on your search strategy, typically you find the data you look for in both data bases--at different places. Sometimes "The Two" are complementary to each other, sometimes an other (third) search engine finds the data on the net that neither ACS nor Reaxys indexed (yet).
Personally, because of the design "how the numerical data are managed" I would suggest Beilstein as the better choice here: if you find your compound, the data base will list in a table wavelength and molecular absorption coefficient altogther with the bibliographic reference -- often including the solvent of the analysis. And the thought occurs to me, it is easier to query with Boolean logic, like "find a compound of molecular mass in the range of xyz to x'y'z with an $\epsilon$ greater than 20000", for example.
Less in coverage -- yet worth to point to are the compilations Sadtlers Handbook of ultraviolet spectra (today part in Bio-Rad's "KnowItAll" database) and the handbook of stains, dyes, and indicators by Sigma-Aldrich, too mention some of the printed references usually found in the section of spectroscopy/chemistry in university libraries. Here you find not only one $\epsilon$ at $\lambda_{\mbox{max}}$, but a complete print of the spectrum. (Be aware, the elder the sources sometimes use wavenumbers or kilo-Kaysers instead of nanometers to reference the wavelength.)
Taking into account your user profile related to quantum chemistry, perhaps you want to train your quantum chemical model with known experimental data, to evolve from a descriptive to a predictive -- and small molecules may serve you well, too. If so, take a look at NIST's webbook based on these references.
Last but not least: Take these data with a grain of salt, often there is some limitation: the same compound / material often exhibits a slightly different UV-Vis absorption spectrum if analyzed once in solvent A, and subsequently in solvent B. Bathochromic / hypsochromic shifts (solvatochromism) may still occur. Solvent polarity is among the parameters in this play.
