SQL Server 2014 :: Comparing String With Date

I have to write a where condition where i need to compare string with date

I have 2 columns FROMDATE and TODATE with datatype varchar(9)

The strings in the columns looks like YYYYMMDD+'1' or YYYYMMDD+'2' here 1 is Am and 2 is PM

i.e., 201401011 or 201401012

So I need to chop off last character before using them in WHERE condition.

Now I need to write a where condition like [if todays date is in between fromdate and todate columns then return rows.

if FROMDATE column is null it should take minimum date 1900/01/01 if TODATE is null then date should be 9999/01/01

The query i wrote is

select * from Table where ISNULL(SUBSTRING(VALIDTO,1,8),'19000101') > = getdate()

AND ISNULL(SUBSTRING(VALIDTO,1,8),'99991231') < convert(varchar, getdate(), 112)

but it shows no data...